Power management in solar powered electronic devices

Abstract

An electronic device powered by a solar panel and a rechargeable battery. The electronic device prevents the rechargeable battery from being depleted by the solar panel when the solar panel cannot provide sufficient energy to power the electronic device. When the rechargeable battery is fully charged, the electronic device prevents unnecessary charging and discharging of the rechargeable battery by disconnecting the rechargeable battery. The electronic device detects and reports a defective rechargeable battery by powering the electronic device by means of a solar panel. The electronic device detects and processes an undervoltage condition when powered by a solar panel by reconnecting a rechargeable battery.

Description

Power management in solar-powered electronic devices

[0001] Related applications

[0002] This application claims priority to U.S. Provisional Application 63 / 540,415, filed September 26, 2023, the contents of which are incorporated herein by reference. Technical Field

[0003] This disclosure generally relates to electronic devices, and more specifically to power management in solar-powered electronic devices. Background Technology

[0004] Solar-powered electronic devices are typically powered by both rechargeable batteries and solar panels. In a typical arrangement, the electronic components of a solar-powered electronic device are powered by rechargeable batteries, and the solar panels are configured to charge the rechargeable batteries.

[0005] Solar-powered electronics need to manage the power generated by solar panels and rechargeable batteries to achieve optimal operation, reliability, and lifespan. Summary of the Invention

[0006] In one aspect of this disclosure, a method is provided in an electronic device including a power management subsystem, a controller, and a plurality of peripheral devices, the electronic device being powered by a solar panel and a rechargeable battery, both of which are connected to the controller and the plurality of peripheral devices at their respective positive terminals. The method includes determining whether the solar panel is connected to a ground terminal at its negative terminal, and disconnecting the negative terminal from the ground terminal in response to determining that the solar panel is connected to the ground terminal. The method also includes reading the voltage at the negative terminal of the solar panel, and connecting the negative terminal of the solar panel to the ground terminal in response to determining, based on the voltage, that the solar panel is generating sufficient electrical energy to power at least some of the plurality of peripheral devices.

[0007] In some implementations, the method further includes: in response to determining, based on the voltage, that the solar panel is not generating sufficient electrical energy to power at least some of the peripheral devices, keeping the negative terminal of the solar panel disconnected from the ground terminal. Advantageously, when the solar panel is not generating electrical energy, the rechargeable battery does not degrade the solar panel cells through solar panel depletion. Because damage to the solar cells is minimized, the lifespan of the solar panel is increased.

[0008] In some implementations, the negative terminal of the solar panel is connected to a ground terminal via an N-channel field-effect transistor (NFET) switch having a source, a gate, and a drain. In such an implementation, the NFET switch is connected to the ground terminal at its source and to the negative terminal of the solar panel at its drain, and determining that the solar panel is generating sufficient energy includes detecting a negative voltage at the drain of the NFET switch. Advantageously, determining that the solar panel is generating sufficient energy is done without connecting the negative terminal of the solar panel to ground. This prevents the rechargeable battery from being depleted by the solar panel during the determination period.

[0009] In some implementations, the negative terminal of the solar panel is connected to a ground terminal via a P-channel field-effect transistor (PFET) switch having a source, a gate, and a drain. In such an implementation, the PFET switch is connected to the ground terminal at its drain and to the negative terminal of the solar panel at its source, and determining that the solar panel is generating sufficient energy includes detecting a negative voltage at the source of the PFET switch. Advantageously, determining that the solar panel is generating sufficient energy is done without connecting the negative terminal of the solar panel to ground. This prevents the rechargeable battery from being depleted by the solar panel during the determination process.

[0010] In some implementations, the negative terminal of the solar panel is connected to a ground terminal via an N-channel field-effect transistor (NFET) switch having a source, a gate, and a drain. In such an implementation, the NFET switch is connected to the ground terminal at its source and to the negative terminal of the solar panel at its drain, and determining that the solar panel is not generating sufficient energy includes detecting a positive voltage at the drain of the NFET switch. Advantageously, determining that the solar panel is not generating sufficient energy is done without connecting the negative terminal of the solar panel to ground. This prevents the rechargeable battery from being depleted by the solar panel during the determination period.

[0011] In some implementations, the negative terminal of the solar panel is connected to a ground terminal via a P-channel field-effect transistor (PFET) switch having a source, gate, and drain. In such an implementation, the PFET switch is connected to the ground terminal at its drain and to the negative terminal of the solar panel at its source, and determining that the solar panel is not generating sufficient energy includes detecting a positive voltage at the source of the PFET switch. Advantageously, determining that the solar panel is not generating sufficient energy is done without connecting the negative terminal of the solar panel to ground. This prevents the rechargeable battery from being depleted by the solar panel during the determination period.

[0012] In some implementations, the negative terminal of the solar panel is connected to a ground terminal via a field-effect transistor (FET) switch, and connecting the negative terminal to the ground terminal includes closing the FET switch.

[0013] In some implementations, reading the voltage at the negative terminal of the solar panel includes activating a voltage sensor connected to the negative terminal of the solar panel and reading the voltage sensor signal. Advantageously, the voltage sensor is activated only when it is necessary to determine whether the solar panel is generating sufficient energy, and disabled otherwise. Keeping the voltage sensor disabled most of the time saves energy.

[0014] In some implementations, the voltage sensor includes an operational amplifier having an inverting input, a non-inverting input, a positive supply terminal, a negative supply terminal, and an output. In such an implementation, the negative supply terminal is connected to the negative terminal of the solar panel, the output of the operational amplifier is connected to the inverting input, and the non-inverting input is connected to ground. Enabling the voltage sensor involves the controller activating a voltage sensor enable signal connected to the positive supply terminal of the operational amplifier. This implementation of the voltage sensor has the advantage of measuring the voltage at the negative supply terminal of the solar panel (which can be positive or negative) while providing a voltage sensor signal that is always positive, thus suitable for conversion to a digital value via, for example, an analog-to-digital converter.

[0015] In some implementations, the voltage sensor signal includes a positive analog signal, and reading the voltage sensor signal includes converting the positive analog signal into a digital value. Advantageously, this digital value can be compared with a specific value in the firmware and used to determine whether to reconnect the solar panel or leave it disconnected.

[0016] In another aspect of this disclosure, an electronic device is provided, comprising a controller, a memory coupled to the controller, and a plurality of peripheral devices. Additionally, the electronic device includes a solar panel coupled to the controller, the memory, and the plurality of peripheral devices. The electronic device also includes a rechargeable battery coupled to the controller, the memory, the plurality of peripheral devices, and the solar panel. Furthermore, the electronic device includes a power management subsystem coupled to the solar panel and the rechargeable battery, the power management subsystem including a voltage sensor connected to the negative terminal of the solar panel and a solar panel bottom switch connected to the negative terminal of the solar panel. The memory stores machine-executable programming instructions that configure the electronic device to: determine whether the solar panel is connected to a ground terminal at its negative terminal via the solar panel bottom switch. In response to determining that the solar panel is connected to the ground terminal at its negative terminal, the machine-executable programming instructions configure the electronic device to disconnect the negative terminal from the ground terminal. The machine-executable programming instructions also configure the electronic device to read the voltage at the negative terminal of the solar panel. In response to determining, based on the voltage, that the solar panel is generating sufficient electrical energy to power at least some of the plurality of peripheral devices, the machine can execute programming instructions to configure the electronic device to connect the negative terminal of the solar panel to the ground terminal.

[0017] In some implementations, the machine-executable programming instructions also configure the electronic device to read the voltage at the negative terminal of the solar panel. In response to determining, based on the voltage, that the solar panel is not generating sufficient electrical energy to power at least some of the plurality of peripheral devices, the machine-executable programming instructions configure the electronic device to keep the negative terminal of the solar panel disconnected from the ground terminal.

[0018] In some implementations, the bottom switch of the solar panel includes an N-channel field-effect transistor (NFET) switch having a source, a gate, and a drain. In such an implementation, the NFET switch is connected to a ground terminal at its source and to the negative terminal of the solar panel at its drain, and the machine-executable programming instructions configured to determine that the solar panel is generating sufficient energy include machine-executable programming instructions that detect a negative voltage at the drain of the NFET switch.

[0019] In some implementations, the bottom switch of the solar panel includes a P-channel field-effect transistor (PFET) switch having a source, a gate, and a drain. In such an implementation, the PFET switch is connected to a ground terminal at its drain and to the negative terminal of the solar panel at its source, and the machine-executable programming instructions for determining that the solar panel is generating sufficient energy include machine-executable programming instructions that configure the electronics to detect a negative voltage at the source of the PFET switch.

[0020] In some implementations, the bottom switch of the solar panel includes an N-channel field-effect transistor (NFET) switch having a source, a gate, and a drain. In such an implementation, the NFET switch is connected to a ground terminal at its source and to the negative terminal of the solar panel at its drain, and machine-executable programming instructions configuring the electronics to determine that the solar panel is not generating sufficient energy include machine-executable programming instructions configuring the electronics to detect a positive voltage at the drain of the NFET switch.

[0021] In some implementations, the bottom switch of the solar panel includes a P-channel field-effect transistor (PFET) switch having a source, a gate, and a drain. In such an implementation, the PFET switch is connected to a ground terminal at its drain and to the negative terminal of the solar panel at its source, and the machine-executable programming instructions for determining that the solar panel is not generating sufficient energy include machine-executable programming instructions that configure the electronic device to detect a positive voltage at the source of the PFET switch.

[0022] In some implementations, the bottom switch of the solar panel includes a field-effect transistor (FET) switch, and the machine-executable programming instructions that configure the electronic device to connect the negative terminal to the ground terminal include machine-executable programming instructions to close the FET switch.

[0023] In some implementations, machine-executable programming instructions configuring the electronic device to read the voltage at the negative terminal of the solar panel include machine-executable programming instructions configuring the electronic device to enable voltage sensor I and read the voltage sensor signal of the voltage sensor.

[0024] In some implementations, the voltage sensor includes an operational amplifier having an inverting input, a non-inverting input, a positive power supply terminal, a negative power supply terminal, and an output terminal. In such an implementation, the negative power supply terminal is connected to the negative terminal of the solar panel, the output terminal of the operational amplifier is connected to the inverting input terminal of the operational amplifier, the voltage sensor signal is the output of the operational amplifier, the non-inverting input terminal of the operational amplifier is connected to ground, and the machine-executable programming instructions for configuring the electronic device to enable the voltage sensor include configuring the electronic device to have the signal connected to the positive power supply terminal of the operational amplifier set to valid machine-executable programming instructions by the controller.

[0025] In some implementations, the voltage sensor signal of the voltage sensor includes a positive analog signal, and the machine-executable programming instructions configuring the electronic device to read the voltage sensor signal include machine-executable programming instructions configuring the electronic device to convert the positive analog signal into a digital value.

[0026] In another aspect of this disclosure, a method is provided in an electronic device including a power management subsystem, a controller, and a plurality of peripheral devices, the electronic device being powered by a solar panel and a rechargeable battery, both of which are connected to the controller and the plurality of peripheral devices via an unregulated voltage bus at their respective positive terminals. The method includes reading the voltage of the unregulated voltage bus. In response to determining that the rechargeable battery is fully charged based on the voltage of the unregulated voltage bus, and in response to determining that the solar panel provides sufficient electrical energy, the method further includes disconnecting the rechargeable battery from the unregulated voltage bus. Advantageously, when the rechargeable battery is already fully charged, repeated and unnecessary discharging and recharging of the rechargeable battery is avoided. This extends battery life.

[0027] In some implementations, determining that the solar panel provides sufficient electrical energy includes disconnecting the negative terminal of the solar panel from the grounding terminal and detecting the negative voltage at the negative terminal of the solar panel using a voltage sensor.

[0028] In some implementations, the voltage sensor includes an operational amplifier having an inverting input, a non-inverting input, a positive power supply terminal, a negative power supply terminal, and an output terminal. In such an implementation, the negative power supply terminal is connected to the negative terminal of the solar panel, the output terminal of the operational amplifier is connected to the inverting input terminal, the voltage sensor signal is the output of the operational amplifier, the non-inverting input terminal of the operational amplifier is connected to ground, and enabling the voltage sensor includes the controller activating the signal connected to the positive power supply terminal of the operational amplifier.

[0029] In some implementations, the voltage sensor signal of the voltage sensor includes a positive analog signal, and reading the voltage sensor signal of the voltage sensor includes converting the positive analog signal into a digital value.

[0030] In some implementations, the negative terminal of the solar panel is connected to a ground terminal via an N-channel field-effect transistor (NFET) switch having a source, a gate, and a drain. In such an implementation, the NFET switch is connected to the ground terminal at its source and to the negative terminal of the solar panel at its drain, and determining that the solar panel is generating sufficient energy includes detecting a negative voltage at the drain of the NFET switch.

[0031] In some implementations, disconnecting the rechargeable battery from the unregulated voltage bus includes: disconnecting the top battery switch between the positive terminal of the rechargeable battery and the unregulated voltage bus, and disconnecting the bottom battery switch between the negative terminal of the rechargeable battery and the ground terminal.

[0032] In some implementations, the method further includes: in response to determining that the rechargeable battery is connected to the unregulated voltage bus, and in response to determining that the rechargeable battery is defective based on the voltage of the unregulated voltage bus, and in response to determining that the solar panel provides sufficient power to power on the network interface of the electronic device, the method further includes powering on the network interface and sending a notification to a remote server indicating that the rechargeable battery is defective.

[0033] In some implementations, the method further includes: connecting the rechargeable battery to the unregulated voltage bus in response to determining that the rechargeable battery is disconnected from the unregulated voltage bus and in response to determining a potential undervoltage condition based on the voltage of the unregulated voltage bus.

[0034] In some implementations, in response to determining that the rechargeable battery is disconnected from the unregulated voltage bus, and in response to determining a potential undervoltage condition based on the voltage of the unregulated voltage bus, and in response to determining that the solar panel is not generating sufficient electrical energy, the method further includes disconnecting the solar panel from the ground terminal at its negative terminal.

[0035] In some implementations, the negative terminal of the solar panel is connected to a ground terminal via an N-channel field-effect transistor (NFET) switch having a source, a gate, and a drain. The NFET switch is connected to the ground terminal at its source and to the negative terminal of the solar panel at its drain, and determining that the solar panel is not generating sufficient energy includes detecting a positive voltage at the drain of the NFET switch.

[0036] In another aspect of this disclosure, an electronic device is provided, comprising a controller; a memory coupled to the controller; a plurality of peripheral devices coupled to the controller; an unregulated voltage bus; a rechargeable battery for providing power to the controller, the memory, and the plurality of peripheral devices via the unregulated voltage bus; a solar panel for recharging the rechargeable battery and for providing power to the controller, the memory, and the plurality of peripheral devices via the unregulated voltage bus; and a power management subsystem coupled to the controller, the rechargeable battery, and the solar panel. The memory stores machine-executable programming instructions that, when executed by the controller, configure the electronic device to read the voltage of the unregulated voltage bus. In response to determining that the rechargeable battery is connected to the unregulated voltage bus, in response to determining that the rechargeable battery is fully charged based on the voltage of the unregulated voltage bus, and in response to determining that the solar panel provides sufficient power, the machine-executable programming instructions configure the electronic device to disconnect the rechargeable battery from the unregulated voltage bus.

[0037] In some implementations, machine-executable programming instructions that configure the electronic device to determine that the solar panel provides sufficient electrical energy include machine-executable programming instructions that configure the electronic device to perform the following operations: disconnecting the negative terminal of the solar panel from the ground terminal and detecting a negative voltage at the negative terminal of the solar panel by a voltage sensor.

[0038] In some implementations, the voltage sensor includes an operational amplifier having an inverting input, a non-inverting input, a positive power supply terminal, a negative power supply terminal, and an output terminal. In such an implementation, the negative power supply terminal is connected to the negative terminal of the solar panel, the output terminal of the operational amplifier is connected to the inverting input terminal, the voltage sensor signal of the voltage sensor is the output of the operational amplifier, the non-inverting input terminal of the operational amplifier is connected to ground, and configuring the electronic device to enable machine-executable programming instructions for the voltage sensor includes configuring the electronic device to have the signal connected to the positive power supply terminal of the operational amplifier set to valid machine-executable programming instructions by the controller.

[0039] In some implementations, the voltage sensor signal of the voltage sensor includes a positive analog signal, and the machine-executable programming instructions configuring the electronic device to read the voltage sensor signal include machine-executable instructions configuring the electronic device to convert the positive analog signal into a digital value.

[0040] In some implementations, the negative terminal of the solar panel is connected to a ground terminal via an N-channel field-effect transistor (NFET) switch having a source, a gate, and a drain. In such an implementation, the NFET switch is connected to the ground terminal at its source and to the negative terminal of the solar panel at its drain, and machine-executable programming instructions configuring the electronics to determine that the solar panel is generating sufficient energy include machine-executable programming instructions configuring the electronics to detect a negative voltage at the drain of the NFET switch.

[0041] In some implementations, machine-executable programming instructions configuring the electronic device to disconnect the rechargeable battery from the unregulated voltage bus include machine-executable programming instructions configuring the electronic device to: disconnect a top battery switch between the positive terminal of the rechargeable battery and the unregulated voltage bus, and disconnect a bottom battery switch between the negative terminal of the rechargeable battery and the ground terminal.

[0042] In some implementations, the machine can execute programming instructions in response to determining that the rechargeable battery is connected to the unregulated voltage bus, in response to determining that the rechargeable battery is defective based on the voltage of the unregulated voltage bus, and in response to determining that the solar panel provides sufficient power, also configure the electronic device to power on the network interface and send a notification indicating that the rechargeable battery is defective to a remote server.

[0043] In some implementations, the machine-executable programming instructions also configure the electronic device to connect the rechargeable battery to the unregulated voltage bus in response to determining that the rechargeable battery is disconnected from the unregulated voltage bus and in response to determining a potential undervoltage condition based on the voltage of the unregulated voltage bus.

[0044] In some implementations, the machine can execute programmable instructions to disconnect the rechargeable battery from the unregulated voltage bus in response to determining that the rechargeable battery is disconnected from the unregulated voltage bus, to determine a potential undervoltage condition based on the voltage of the unregulated voltage bus, and to disconnect the solar panel from the ground terminal at its negative terminal in response to determining that the solar panel is not generating sufficient electrical energy.

[0045] In some implementations, the negative terminal of the solar panel is connected to a ground terminal via an N-channel field-effect transistor (NFET) switch having a source, a gate, and a drain. In such an implementation, the NFET switch is connected to the ground terminal at its source and to the negative terminal of the solar panel at its drain, and machine-executable programming instructions configuring the electronics to determine that the solar panel is not generating sufficient energy include machine-executable programming instructions configuring the electronics to detect a positive voltage at the drain of the NFET switch. Attached Figure Description

[0046] Exemplary, non-limiting embodiments of this disclosure are described with reference to the accompanying drawings, in which:

[0047] Figure 1 is a schematic diagram of a telematics system including an asset tracker coupled to engineless assets;

[0048] Figure 2 is a perspective view of an exemplary electronic device in the form of a solar-powered asset tracker;

[0049] Figure 3 is a block diagram of an exemplary electronic device in the form of a solar-powered asset tracker;

[0050] Figure 4 is a block diagram illustrating the various components of the power management module of the solar-powered asset tracker of Figure 3, shown in combination with a controller, a solar panel, and a rechargeable battery, according to an embodiment of the present disclosure.

[0051] Figure 5 is a flowchart of a method for controlling a solar panel in an electronic device powered by solar energy according to an embodiment of the present disclosure.

[0052] Figure 6 is a schematic diagram illustrating the implementation of a solar panel bottom voltage sensor and a solar panel bottom switch according to an embodiment of the present disclosure;

[0053] Figure 7 is a schematic diagram depicting an exemplary implementation of a solar panel current sensor circuit according to an embodiment of the present disclosure;

[0054] Figure 8 is a schematic diagram depicting an exemplary implementation of a rechargeable battery current sensor circuit according to an embodiment of the present disclosure.

[0055] Figure 9 is a schematic diagram depicting exemplary implementations of a top battery switch and a bottom battery switch according to embodiments of the present disclosure;

[0056] Figure 10 is a flowchart of a method performed by an electronic device having a solar panel and a rechargeable battery according to an embodiment of the present disclosure; and

[0057] Figure 11 is a simplified circuit diagram of a voltage sensor used to measure the voltage of an unregulated voltage bus. Detailed Implementation

[0058] This disclosure generally relates to solar-powered electronic devices powered by rechargeable batteries and solar panels. More specifically, this disclosure provides a power management module for solar-powered electronic devices. The power management module uses a combination of discrete electronic components and firmware to manage the operation and configuration of both the rechargeable battery and the solar panel. Additionally, this disclosure provides a method for power management of solar-powered electronic devices.

[0059] An example of a solar-powered electronic device is a solar-powered asset tracker. An asset tracker is an electronic device deployed on an asset to track its location and status. Asset trackers are typically part of an asset tracking system. An asset tracking system allows an administrator to track the location and status of one or more assets. Assets can be vehicles, pieces of equipment, containers, trailers, tanks, or any other type of asset whose location and status need to be tracked. However, the power management modules and methods for power management of solar-powered electronic devices presented in this disclosure are not limited to such implementations.

[0060] The solar-powered electronic devices discussed in this disclosure are electronic devices that can actually operate on rechargeable batteries and / or solar panels. Examples of solar-powered electronic devices include, but are not limited to, asset trackers; communication and signal enhancers, such as Wi-Fi extenders or cellular signal enhancers; electronic weather stations, including rain gauges, temperature sensors, anemometers, and barometers; electronic wireless surveillance systems, including camera devices, motion sensors, and communication modules; ventilation systems, such as loft fans and ventilation systems for vehicles; and any other electronic devices that utilize both solar panels and rechargeable batteries.

[0061] In this disclosure, "solar panel" refers to a portable solar panel suitable for use with electronic devices, rather than a large solar panel typically installed on the roof of a building. A portable solar panel is a compact and lightweight energy harvesting device that converts sunlight into electrical energy using photovoltaic cells. Photovoltaic cells are made of materials that generate electrons when exposed to light. Portable solar panels are designed to provide convenient and renewable power to a variety of portable electronic devices, such as solar-powered asset trackers. As described in detail below, the electrical energy generated by the solar panel can be used to charge rechargeable batteries and / or power various components of a solar-powered asset tracker. Common types of portable solar panels for portable electronic devices include monocrystalline solar panels, polycrystalline solar panels, and thin-film solar panels. Each photovoltaic cell in a monocrystalline solar panel uses a single silicon crystal, while each photovoltaic cell in a polycrystalline solar panel uses multiple silicon crystals fused together. Thin-film solar cells are made by depositing one or more thin layers of photovoltaic material onto a substrate such as glass, plastic, or metal.

[0062] A rechargeable battery is a battery that can be charged and discharged multiple times to make it reusable. Rechargeable batteries can be recharged using electrical energy to restore their energy storage capacity for future use. Rechargeable batteries can be any of the following types: nickel-cadmium (Ni-Cd), nickel metal hydride (NiMH), lithium-ion (Li-ion), or lithium polymer (LiPo). Ni-Cd batteries are less common because they have relatively low energy density compared to other rechargeable battery types and are affected by the memory effect. NiMH batteries have better energy density than Ni-Cd batteries but are still affected by the memory effect. Li-ion batteries are widely used because they have higher energy density than Ni-Cd and NiMH and do not have the memory effect. Variations of Li-ion batteries include lithium cobalt oxide (LiCoO2), lithium iron phosphate (LiFePO4), lithium nickel manganese cobalt oxide (Li-NMC), and lithium nickel cobalt aluminum oxide (Li-NCA). LiPo batteries include pouch cell LiPo batteries and cylindrical cell LiPo batteries.

[0063] The following describes a non-limiting implementation of a solar-powered electronic device operating in an asset tracking system environment.

[0064] Asset tracking system

[0065] Asset tracking systems facilitate the tracking and monitoring of the location, movement, and status of various assets. Asset tracking systems can be used in logistics, transportation, supply chain management, and other industries. An asset tracker is a device coupled to an asset to track and monitor its location, movement, and status. Assets can be vehicles, valuable equipment, containers, trailers, tanks, or any other type of asset whose location, movement, and status need to be tracked. An asset tracker is an electronic device that includes at least one of a positioning module, an inertial measurement unit, and one or more sensors. The positioning module determines the asset tracker's location, thereby determining the asset's location. The inertial measurement unit detects motion, orientation, and heading. One or more sensors determine the conditions experienced by the asset tracker, such as temperature, pressure, noise, etc. The asset tracker periodically transmits its location, movement, and / or status to a remote server, such as an asset tracking server. Therefore, the location, movement, and / or status of assets can be tracked in real-time or near real-time.

[0066] Figure 1 shows a high-level block diagram of an asset tracking system 101. The asset tracking system 101 includes an asset tracker 200 deployed in asset 100, a network 50, an asset tracking server 130, a management terminal 140, and a satellite 170. Although a single instance of each element is shown for simplicity, multiple instances of each shown element are common in asset tracking systems.

[0067] Asset 100 shown is in the form of a container placed on a trailer 105, which is coupled to a tractor unit 110. Asset 100 can be a container, vehicle, industrial equipment, construction equipment, tanks containing chemicals, or any other asset whose location, movement, and / or condition needs to be tracked. Asset 100 can be transported by the trailer 105 shown, or by ship, train, aircraft, or any other means of transport. Asset 100 can also be an industrial or construction piece of equipment, such as a generator, concrete mixer, compressor, etc. Assets of this type may have wheels and may be towed from one location to another.

[0068] Asset tracker 200 is an electronic device that can be coupled to an asset (e.g., asset 100). Asset tracker 200 is configured to track the location, movement, and / or status of asset 100. Asset tracker 200 can be battery-powered or solar-powered. Battery-powered asset trackers are electronic asset trackers powered by non-rechargeable batteries. Solar-powered asset trackers are powered by solar panels and rechargeable batteries. A detailed description of the internal components of a solar-powered asset tracker 300 is described with reference to FIG3, according to an embodiment of this disclosure. The solar-powered asset tracker 300 is an example of a solar-powered electronic device powered by a rechargeable battery and a solar panel. Asset tracker 200 utilizes a Global Navigation Satellite System (GNSS) to obtain its location. In the depicted embodiment, asset tracker 200 communicates with satellite 170 to obtain its location. Asset tracker 200 also includes an inertial measurement unit (IMU) and / or sensors, such as temperature sensors, light sensors, and pressure sensors. The combination of location data, movement, and sensor data is referred to as asset tracking data 112. Asset tracker 200 is connected to network 50, which allows asset tracker 200 to send asset tracking data 112 to remote servers such as asset tracking server 130.

[0069] Network 50 can be a single network or a combination of networks such as data cellular networks, wide area networks, the Internet, and other network technologies. Network 50 provides connectivity between asset tracker 200 and asset tracking server 130, as well as connectivity between management terminal 140 and asset tracking server 130.

[0070] In several implementations of the asset tracking system 101, network 50 is a cellular network utilizing cellular technology. In one implementation, network 50 uses second-generation (2G) cellular technology based on the Global System for Mobile Communications (GSM) protocol and supporting data transmission protocols such as General Packet Radio Service (GPRS) or Enhanced Data Rate GSM Evolution (EDGE). In another implementation, network 50 uses third-generation (3G) cellular technology utilizing the Universal Mobile Telephone System (UMTS) which supports data transmission using the High-Speed ​​Packet Access (HSPA) protocol. In yet another implementation, network 50 uses fourth-generation (4G) cellular technology using the Long Term Evolution (LTE) protocol. In yet another implementation, network 50 uses fifth-generation (5G) cellular technology. In yet another implementation, network 50 uses Narrowband Internet of Things (NB-IoT), a low-power wide-area network (LPWAN) technology that is part of the 3rd Generation Partnership Project (3GPP) standard.

[0071] In some implementations of the asset tracking system 101, network 50 includes a WAN using non-cellular wide area network (WAN) technology. One example of a non-cellular WAN technology that network 50 can use is WiMAX (Microwave Access Global Interoperability) based on the IEEE 810.16 family of standards. TM Another example of a non-cellular WAN technology that Network 50 can use is LoRaWAN (LoRa Wide Area Network). TM This technology is a low-power WAN protocol. Another example of a non-cellular WAN technology that Network 50 can use is Weightless, a family of open standard low-power WAN (LPWAN) technologies that operate in the sub-GHz band.

[0072] In some implementations of the asset tracking system 101, when the asset tracker 200 is coupled to an asset providing a wired network connection, the network 50 uses wired network technology. Examples of wired network technologies include Ethernet, Fast Ethernet, and LocalTalk. TM Token Ring, Fiber Distributed Data Interface (FDDI), and Asynchronous Transfer Mode (ATM).

[0073] In some implementations, network 50 is a combination of the technologies specified above.

[0074] Asset tracking server 130 is an electronic device capable of executing machine-executable programmable instructions for receiving, storing, and analyzing asset tracking data 112. Asset tracking server 130 can be implemented as a single computer system or a cluster of computers. Asset tracking server 130 can utilize operating systems such as Linux, Windows, Unix, FreeBSD, macOS Server, VMware ESXi, Microsoft Hyper-V Server, Oracle Solaris, IBM AIX, or any other equivalent operating system. Alternatively, asset tracking server 130 can be implemented on a cloud computing platform such as Amazon Web Services (AWS), Microsoft Azure, Google Cloud Platform (GCP), IBM Cloud, Oracle Cloud, and Alibaba Cloud. Asset tracking server 130 is connected to network 50 and can receive asset tracking data 112 from asset tracker 200. Asset tracking server 130 may have multiple software modules for performing data analysis and analytics on telematics data to obtain useful asset information about asset 100. Asset tracking server 130 can be coupled to asset tracking database 132, which stores telematics data and / or analysis results related to asset 100. Asset tracking server 130 can transmit asset tracking data 112 about asset 100 to management terminal 140.

[0075] Satellite 170 may be part of a Global Navigation Satellite System (GNSS), a satellite-based navigation system that provides positioning, navigation, and timing services globally. The four major GNSS systems currently in operation are Global Positioning System (GPS), Global Navigation Satellite System (GLONASS), Galileo, and BeiDou. GPS is developed and operated by the United States, GLONASS is Russia's equivalent of GPS, Galileo is the European Union's GNSS, and BeiDou is China's GNSS system. Other less commonly used GNSS systems are QZSS (Japan) and IRNSS or NavIC (India). Positioning information can be processed by a positioning module on asset tracker 200 to provide positioning data indicating the positioning of asset tracker 200 (and thus the positioning of asset 100 coupled to it). As outlined below, in other implementations (not shown), asset tracker 200 may use other means to determine its positioning.

[0076] Management terminal 140 is an electronic device capable of connecting to asset tracking server 130 via network 50. The management terminal can be configured to: retrieve data and analysis related to one or more assets 100; receive alerts from asset tracking server 130 regarding one or more conditions on asset trackers 200; or issue commands to one or more asset trackers 200 via asset tracking server 130. Management terminal 140 is shown as a laptop computer; however, this is not necessarily the case. The management terminal can be a desktop computer, industrial human-machine interface (HMI), touchscreen panel, table, smartphone, augmented reality (AR) headset, or network operations center (NOC). Management terminal 140 can run a web browser or custom application that allows retrieval of data and analysis about one or more assets 100 from asset tracking server 130 via its network interface. Management terminal 140 can also be used to issue commands to one or more asset trackers 200 via asset tracking server 130. Administrator 11 can use management terminal 140 to communicate with asset tracking server 130. In addition to retrieving and analyzing data, the management terminal 140 allows the administrator 11 to set up alarms and geofences for keeping track of the asset 100, receiving transmitted notifications, and so on.

[0077] In operation, asset tracker 200 is coupled to asset 100 to capture the asset's location, motion, and / or one or more conditions related to the asset. Location data is determined by a positioning module communicating with satellite 170. Motion data is determined by an inertial measurement unit (IMU), which is part of or coupled to asset tracker 200. One or more conditions are determined based on sensor data collected from sensors within asset tracker 200 or external sensors coupled to asset tracker 200. The combination of location data, motion data, and / or sensor data comprises asset tracking data 112. Asset tracker 200 transmits asset tracking data 112 to asset tracking server 130 via network 50. Asset tracking server 130 can process, aggregate, and analyze asset tracking data 112 to generate asset information about asset 100. Asset tracking server 130 can store asset tracking data 112 and / or the generated asset information in asset tracking database 132. Management terminal 140 can connect to asset tracking server 130 via network 50 to access asset tracking data 112 and / or generated asset information. Alternatively, asset tracking server 130 can push asset tracking data 112 and / or generated asset information to management terminal 140. Administrator 11 can use management terminal 140 to set alarms for certain activities related to asset 100. When alarm criteria are met, asset tracking server 130 sends a message to management terminal 140 to notify administrator 11. For example, when an asset is moved outside its service area, asset tracking server 130 can send an alarm message to management terminal 140. Administrator 11 can also use management terminal 140 to configure asset tracker 200 by issuing commands to asset tracker 200 via asset tracking server 130. For example, asset tracking server 130 can issue commands to asset tracker 200 in response to certain conditions to capture certain types of sensor data.

[0078] Solar-powered asset tracker

[0079] As an example of an electronic device powered by a rechargeable battery and a solar panel, a solar-powered asset tracker 300 is described with reference to Figures 2 and 3.

[0080] Figure 3 is a perspective view of a solar-powered asset tracker 300 according to an embodiment of the present disclosure. The solar-powered asset tracker 300 has a housing 202 for accommodating the internal components of the asset tracker 300. On the top surface 203 of the housing 202, there is a solar panel 250 that acts as an energy harvester for the solar-powered asset tracker 300. When deployed, the solar-powered asset tracker 300 is coupled to an asset and positioned to be optimally exposed to sunlight. For example, the solar-powered asset tracker 300 is typically attached to the top surface of the asset to expose it to direct sunlight.

[0081] Figure 3 is a block diagram of a solar-powered asset tracker 300 according to an embodiment of the present disclosure. The solar-powered asset tracker 300 is an example of a solar-powered electronic device.

[0082] The solar-powered asset tracker 300 includes a controller 230. Multiple peripheral devices are coupled to the controller 230 via different types of interfaces. These peripheral devices include a memory 240, a network interface 220, an IMU 290, a short-range wireless communication module 270, a sensor 204, a positioning module 206, and a serial communication module 280. The solar-powered asset tracker 300 also includes a solar panel 250 and a rechargeable battery 210. A power management subsystem 400 couples the solar panel 250 to the rechargeable battery 210, the controller 230, and the peripheral devices. As will be discussed below, some of the peripheral devices shown may be optional.

[0083] Controller 230 may include one or any combination of the following: a processor, microprocessor, microcontroller (MCU), central processing unit (CPU), system-on-a-chip (SoC), processing core, state machine, logic gate array, application-specific integrated circuit (ASIC), field-programmable gate array (FPGA), or any other hardware component or combination of hardware components capable of executing machine-executable programmable instructions. Controller 230 may follow a von Neumann architecture, Harvard architecture, or a modified Harvard architecture. Controller 230 may be a Complex Instruction Set Computer (CISC) processor supporting a complex instruction set, which can perform multiple operations in a single instruction. Alternatively, controller 230 may be a Reduced Instruction Set Computer (RISC) processor with a simplified and streamlined instruction set and employs a pipelined architecture to optimize execution. Controller 230 may have a single processor core or multiple processor cores supporting parallel execution of instructions. Controller 230 may have internal memory for storing machine-executable programmable instructions that will be executed by controller 230 to perform the steps of the methods described in this disclosure.

[0084] Memory 240 is an electronic storage component capable of storing data and machine-executable programmable instructions. Memory 240 may be a read-only memory (ROM), including programmable ROM (PROM), erasable programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM), or flash memory. Memory 240 may be random access memory (RAM), including static RAM (SRAM) and dynamic RAM (DRAM). Alternatively, memory 240 may be ferroelectric RAM (FRAM), magnetic random access memory (MRAM), or phase-change memory (PCM). Memory 240 may also be any combination of the foregoing types. Memory 240 is used to store machine-executable programmable instructions and / or data to support the functions described in this disclosure. Memory 240 is coupled to controller 230 via a memory bus, thereby enabling controller 230 to execute machine-executable programmable instructions stored in memory 240 and access data stored therein.

[0085] Positioning module 206 provides the location of asset tracker 200. In some implementations, positioning module 206 is a Global Navigation Satellite System (GNSS) transceiver using one or more of the GNSS technologies described above. In other implementations, positioning module 206 uses cellular tower triangulation via a cellular network to determine the location of the solar-powered asset tracker 300. In this case, positioning module 206 is coupled to network interface 220, which in this case is a cellular modem for receiving signal measurement results from multiple nearby cellular towers. Positioning module 206 uses the signal measurement results to estimate the location of solar-powered asset tracker 300. The location information determined by positioning module 206 is sent to controller 230. The location data can be in the form of latitude and longitude, or in Universal Transverse Mercator (UTM) coordinates.

[0086] Sensor 204 can be one or more of the following: a temperature sensor, a pressure sensor, an optical sensor, a humidity sensor, a gas sensor, an acoustic sensor, a pH sensor, a soil moisture sensor, or any other suitable sensor indicating the condition of asset 100 coupled to the solar-powered asset tracker 300. Sensor 204 is coupled to the controller via any of serial, parallel, or bus technologies. For example, some of sensors 204 may be connected to controller 230 via a parallel interface. Other sensors 204 may be connected to controller 230 via a bus using any of the known bus technologies, such as Industry Standard Architecture (ISA), Extended ISA (EISA), Micro Channel Architecture (MCA), Video Electronics Standards Association (VESA), Peripheral Component Interconnect (PCI), PCI Express (PCI-X), Personal Computer Memory Card Industry Association (PCMCIA), Accelerated Graphics Port (AGP), and Small Computer System Interface (SCSI). Sensor 204 may be connected to the controller via a serial link such as Universal Asynchronous Receiver / Transmitter (UART), Serial Peripheral Interface (SPI), or Internal Integrated Circuit (I2C). Sensor 204 provides sensor data to controller 230. Some asset trackers may not have any sensors 204 and may only provide location information and / or IMU information. Some asset trackers may have the ability to pair with external sensors via wired or wireless interfaces.

[0087] IMU 290 is an inertial measurement unit. IMU 290 is a device used to measure and provide information about the motion, orientation, and acceleration of an asset tracker. IMU 290 may include several components that work together. For example, IMU 290 may include one or more accelerometers, gyroscopes, magnetometers, and barometers. Accelerometers measure linear acceleration on three axes (typically X, Y, and Z). Gyroscopes measure angular velocity or rotational rate about each of the three axes. Magnetometers measure the strength and direction of a magnetic field and thus determine heading or orientation relative to the Earth's magnetic field. Barometers measure atmospheric pressure, and this can be used to estimate changes in altitude. Some IMUs include a microcontroller or processor that runs sensor fusion algorithms to combine and process data from the various sensors described above. Other IMUs include a communication interface for interfacing with an external microcontroller or processor. Some asset trackers may not include an IMU unit and may report motion determined based on changes in positioning reported by positioning module 206. The IMU 290 can communicate with the controller via a parallel interface, a serial interface using any of the serial technologies described above, a bus interface using any of the bus technologies described above, or it can be directly connected to the general purpose input / output (GPIO) pins and interrupt pins of the controller 230.

[0088] In some implementations, network interface 220 includes a cellular modem utilizing cellular technology. In one implementation, network interface 220 uses second-generation (2G) cellular technology based on the Global System for Mobile Communications (GSM) protocol and supporting data transmission protocols such as General Packet Radio Service (GPRS) or Enhanced Data Rate GSM Evolution (EDGE). In another implementation, network interface 220 uses third-generation (3G) cellular technology utilizing the Universal Mobile Telephone System (UMTS) supporting data transmission using the High-Speed ​​Packet Access (HSPA) protocol. In yet another implementation, network interface 220 uses fourth-generation (4G) cellular technology using the Long Term Evolution (LTE) protocol. In yet another implementation, network interface 220 uses fifth-generation (5G) cellular technology. In yet another implementation, network interface 220 uses Narrowband Internet of Things (NB-IoT), a low-power wide-area network (LPWAN) technology that is part of the 3rd Generation Partnership Project (3GPP) standard.

[0089] In some implementations, network interface 220 includes a WAN modem using non-cellular wide area network (WAN) technology. Network interface 220 can use non-cellular WAN technology. One example of a non-cellular WAN technology that network interface 220 can use is WiMAX, a microwave access global interoperability technology based on the IEEE 810.16 family of standards. TM Another example of a non-cellular WAN technology that network interface 220 can use is LoRaWAN (LoRa Wide Area Network). TM This technology is a low-power WAN protocol. Another example of a non-cellular WAN technology that can be used on a network interface is weightless technology, which is a family of open standard low-power WAN (LPWAN) technologies that operate in the sub-GHz band.

[0090] In some implementations, when the solar-powered asset tracker 300 is coupled to an asset providing wired network connectivity, the network interface 220 uses wired networking technology. Examples of wired networking technologies include Ethernet, Fast Ethernet, and LocalTalk. TM Token Ring, Fiber Distributed Data Interface (FDDI), and Asynchronous Transfer Mode (ATM).

[0091] The network interface 220 can be integrated into the controller, or coupled to the controller via a parallel interface, a serial interface using any of the serial technologies described above, a bus interface using any of the bus technologies described above, or can be directly connected to the general purpose input / output (GPIO) pins and interrupt pins of the controller 230.

[0092] Network interface 220 is used to send asset tracking data 112 to asset tracking server 130 via network 50. Network interface 220 can also be used to receive instructions from asset tracking server 130 for configuring solar-powered asset tracker 300 in a certain mode and / or requesting specific types of asset tracking data 112 from asset 100.

[0093] The short-range wireless communication module 270 is a component designed to provide short-range wireless communication capability to a solar-powered asset tracker 300. The short-range wireless communication module 270 includes at least one of the following: Bluetooth. TM Module, Wi-Fi TM ) module, Zigbee TM Module, Near Field Communication (NFC) TM ) module, Z-Wave module and radio frequency identification (RFID) TM Alternatively, the short-range wireless communication module 270 may include any other short-range wireless communication module. Bluetooth is a widely used wireless technology used for short-range communication between devices. Bluetooth operates in the 2.4 GHz band and supports different versions with different data rates and ranges. Wi-Fi is a wireless communication technology commonly used for local area network (LAN) connections. Wi-Fi operates in different frequency bands, including 2.4 GHz and 5 GHz, and offers higher data rates compared to Bluetooth. NFC is a short-range wireless communication technology that allows devices to establish communication by bringing them close together (typically within a few centimeters). Zigbee is a low-power wireless communication protocol designed for short-range communication in wireless sensor networks, operating according to the IEEE 810.15.4 standard. Z-Wave is a wireless communication technology operating in the sub-GHz frequency range, allowing for longer range and better wall penetration compared to some other wireless technologies. RFID is a technology that uses electromagnetic fields to wirelessly identify and track objects or individuals. It consists of tags or labels that store data and readers that send and receive signals to interact with the tags. The short-range wireless communication module 270 allows other devices to communicate with the solar-powered asset tracker 300 via a short-range wireless network. For example, an external wireless sensor can transmit sensor data to the solar-powered asset tracker 300 via the short-range wireless communication module 270.

[0094] Serial communication module 280 is an example of a wired communication module. Serial communication module 280 is an electronic peripheral device used to provide serial wired communication to the solar-powered asset tracker 300. For example, serial communication module 280 can be one of the following: Universal Asynchronous Receiver / Transmitter (UART), Serial Peripheral Interface (SPI), Internal Integrated Circuit (I2C) module, Controller Area Network (CAN) transceiver, or RS-232 transceiver. UART supports synchronous data transmission between devices and supports relatively low data rates. SPI is a synchronous serial communication protocol that allows devices to exchange data in full-duplex mode. I2C is a serial communication protocol that enables devices to communicate using a two-wire interface. CAN is a serial communication bus commonly used in automotive and industrial applications. In some examples, serial communication module 280 allows external devices to connect to the solar-powered asset tracker 300 to download asset tracking data 112 from it. In other examples, the serial communication module allows external sensors to send sensor data to the solar-powered asset tracker 300.

[0095] The rechargeable battery 210 is used to power the solar-powered asset tracker 300 in conjunction with the solar panel 250. Rechargeable batteries are energy storage devices that can be reused multiple times by recharging them after they are depleted. Rechargeable batteries provide a more sustainable and cost-effective alternative to disposable, single-use batteries. The use of rechargeable batteries is suitable because the solar-powered asset tracker 300 can be deployed in the field for months or even years and can be recharged by the solar panel. Using rechargeable batteries avoids the need to access the asset tracker frequently or periodically to replace non-rechargeable batteries. The rechargeable battery 210 can be any of the rechargeable battery technologies described above.

[0096] Solar panel 250 is a portable solar panel (as shown in Figure 2) mounted on the housing 202 of the solar-powered asset tracker 300. Solar panel 250 can be any of the types of solar panels described above. Solar panel 250 is coupled to the rechargeable battery 210 and peripheral devices of the solar-powered asset tracker 300 via power management subsystem 400.

[0097] The power management subsystem 400 is a subsystem composed of multiple electronic components that control the operation of the rechargeable battery 210 and the solar panel 250 to achieve optimal operation and lifespan of the solar-powered asset tracker 300, which will be described in further detail below.

[0098] In operation, controller 230 may receive one or more of the following: sensor data from sensor 204, positioning data from positioning module 206, motion and / or orientation data from IMU 290, and other data from short-range wireless communication module 270 or serial communication module 280. In general, the collected data includes asset tracking data 112. Controller 230 transmits asset tracking data 112 to asset tracking server 130 via network interface 220 through network 50.

[0099] In some implementations, the solar-powered asset tracker 300 receives commands from the asset tracking server 130 via network interface 220 through network 50. The received commands instruct the asset tracker 200 to be configured in a specific manner. For example, the received commands may configure the solar-powered asset tracker 300 to collect asset tracking data 112 in a specific way.

[0100] Problems with traditional solar-powered electronic devices

[0101] In conventional solar-powered electronic devices, when solar energy is available, solar panel 250 generates electrical energy to charge rechargeable battery 210. When solar energy is unavailable or low, rechargeable battery 210 powers various components of the solar-powered asset tracker 300. The inventors have identified many problems with conventional solar-powered electronic devices.

[0102] In traditional solar-powered electronic devices, the device and its peripherals are always powered by rechargeable batteries. Therefore, a solar panel is connected to the rechargeable battery. When sunlight shines on the solar panel, it generates electricity to charge the battery. When there is little or no sunlight, the device operates solely on the battery. A typical arrangement includes a series switch that connects the solar panel to the battery when it needs charging; otherwise, the switch is disconnected. Due to this electrical arrangement, traditional solar-powered electronic devices encounter numerous problems.

[0103] One problem with conventional power management setups in solar-powered electronic devices is the inability to promptly report failed batteries for replacement. In the example of a solar-powered asset tracker 300, the tracker has a network interface 220 and is capable of sending messages to an asset tracking server 130. However, if the tracker relies on a rechargeable battery 210 and the battery fails, the tracker will cease operation. The administrator 11 will not know the true reason why the tracker has stopped sending any asset tracking data 112. As will be presented below, this disclosure overcomes this problem by detecting the condition of a failed rechargeable battery and powering the tracker 300 with solar panels 250. Advantageously, the tracker 300 is able to operate and send a message to the asset tracking server 130 reporting the condition of the failed rechargeable battery. Therefore, the administrator 11 is informed that the rechargeable battery 210 needs to be replaced.

[0104] Another problem with conventional power arrangements in solar-powered electronics is the unnecessary charging and discharging of rechargeable batteries. As is known in the art, the lifespan of rechargeable batteries is shortened by the number of discharge / recharge cycles they undergo. In conventional arrangements, solar-powered electronics still rely on rechargeable batteries to operate even when sunlight is shining on the solar panels. This results in the rechargeable batteries discharging and then being recharged by the solar panels. Consequently, the lifespan of the rechargeable batteries is shortened, and they eventually fail prematurely. When the rechargeable batteries fail, the solar-powered electronics need to be replaced or at least maintained to replace the batteries, leading to an interruption in the operation of the solar-powered electronics. For solar-powered asset trackers deployed in the field, service interruptions related to battery or asset tracker replacements can result in asset tracking data 112 no longer being transmitted. Therefore, assets may be misplaced or lost without the administrator 11's knowledge. The cost of maintaining or replacing solar-powered asset trackers is another consideration. In this disclosure, the problem of shortened lifespan due to repeated discharge / recharge of the rechargeable battery is addressed by disconnecting the fully charged rechargeable battery 210 from the solar panel 250, and allowing the solar panel 250 to power the solar-powered asset tracker 300 (provided the solar panel 250 can provide sufficient electrical energy for the operation of the solar-powered asset tracker 300). Advantageously, the number of discharge / recharge cycles of the rechargeable battery 210 is reduced, thereby increasing the lifespan of the rechargeable battery 210. Therefore, the solar-powered asset tracker 300 or any other solar-powered electronic device can operate for a longer period without the need for maintenance or replacement.

[0105] When the solar-powered asset tracker 300 is powered solely by the solar panel 250 (because the rechargeable battery 210 is fully charged and disconnected), there may be situations where the power delivered by the solar panel 250 is insufficient to power certain peripheral devices (such as the network interface 220). In such cases, the power management subsystem 400 is configured by the controller 230 to temporarily enable the rechargeable battery 210 to perform certain functions that require a higher power output than the solar panel 250 can deliver.

[0106] Another problem that can be encountered in conventional power arrangements in solar-powered equipment is that the rechargeable battery 210 can be depleted through the solar panel 250 when it is not generating any power, such as at night or in dark areas such as tunnels. The depletion of the rechargeable battery 210 through the solar panel 250 degrades the cells of the solar panel 250, thus shortening its lifespan. In this disclosure, when the solar panel 250 is not generating any power, it is disconnected so that the rechargeable battery 210 is not depleted through the solar panel. Advantageously, this reduces the degradation of the solar panel 250, and the solar-powered asset tracker 300 can operate in the field for a longer duration without the need for maintenance or solar panel replacement.

[0107] As mentioned above, the power management subsystem 400 of the asset tracker 200 includes multiple components. As will be described below, some of these components are discrete components, while others are integrated circuits (ICs). A simplified block diagram of the power management subsystem 400 is shown in Figure 4.

[0108] Figure 4 illustrates various components of a solar panel 250, a rechargeable battery 210, and a controller 230, along with a power management subsystem 400, according to an embodiment of this disclosure. The power management subsystem 400 includes: a solar panel bottom voltage sensor 405, a solar panel bottom field-effect transistor (FET) switch 410, a solar panel current sensor 415, a rechargeable battery current sensor 425, a top battery switch 420, a bottom battery switch 430, an unregulated voltage sensor 435, a large-capacity capacitor 440, and a drop threshold detector 445. Peripherals of the solar-powered asset tracker 300 are represented by loads 480. For example, load 480 may represent one or more of the following: sensor 204, positioning module 206, IMU 290, network interface 220, short-range wireless communication module 270, and serial communication module 280. A description of each component and its function is given below.

[0109] A solar panel bottom voltage sensor 405 is connected at one end to the negative terminal of the solar panel 250 and at the other end to a solar panel bottom FET switch 410. The solar panel bottom voltage sensor 405 measures the solar panel voltage (“solar panel bottom voltage 408”), which represents the voltage at the negative terminal of the solar panel 250. As will be explained below, the solar panel bottom voltage 408 indicates whether the solar panel 250 is generating sufficient electrical energy to power the peripheral devices of the solar-powered asset tracker 300. A schematic diagram of the implementation of the solar panel bottom voltage sensor 405 is shown in Figure 6.

[0110] The solar panel bottom FET switch 410 is an electronic switch used to connect / disconnect the solar panel 250 from the rechargeable battery 210 and the rest of the peripheral equipment (represented by the load 480). The solar panel bottom FET switch 410 is implemented as such, rather than as a general electronic switch, for the reasons provided below. As shown, the solar panel bottom FET switch 410 is implemented as an N-channel field-effect transistor (NFET). Hereinafter, the solar panel bottom FET switch 410 will be referred to as the solar panel bottom NFET 410. For the solar panel bottom NFET 410, the drain (D) is connected to the negative terminal of the solar panel 250, and the source (S) is connected to the ground terminal 490. The gate (G) is connected to the output pin of the controller 230, allowing the controller to open or close the solar panel bottom NFET 410. When the solar panel bottom NFET 410 is closed, current can flow through it. When the NFET 410 at the bottom of the solar panel is off, current cannot flow from the drain to the source, but it can flow from the source to the drain through what is known as the body diode between the source and drain. As described below, this characteristic of the NFET allows detection of whether the solar panel 250 is generating electricity. However, it should be noted that if a P-channel field-effect transistor (PFET) is connected such that its source is connected to the negative terminal of the solar panel 250 and its drain is connected to ground terminal 490, the PFET will also operate.

[0111] To illustrate how the solar-powered asset tracker 300 determines whether the solar panel 250 is generating sufficient power, the following discussion considers both the case where the NFET 410 at the bottom of the solar panel is closed and the case where the NFET 410 at the bottom of the solar panel is open.

[0112] First, let's discuss the case where the NFET 410 at the bottom of the solar panel is closed. When the solar panel 250 is providing sufficient power, current flows from the positive terminal (+) of the solar panel 250 towards the rechargeable battery 210 and other peripheral devices represented by the load 480. In this case, current flows from ground to the negative terminal (-) of the solar panel 250. The voltage at the bottom of the solar panel 408 is 0 V because point 408 is connected to ground. When the solar panel 250 is not providing sufficient power, current flows from the rechargeable battery 210 into the positive terminal (+) of the solar panel 250, out from the negative terminal (-) of the solar panel 250, and reaches ground through the NFET 410 at the bottom of the solar panel. In this case, the voltage at the bottom of the solar panel 408 is 0 V because point 408 is connected to ground. The above demonstrates that when the NFET at the bottom of the solar panel is closed, the solar-powered asset tracker 300 cannot determine whether the solar panel is providing sufficient power.

[0113] Next, we discuss the case where the NFET 410 at the bottom of the solar panel is off. When the solar panel 250 is providing sufficient power, current flows from the positive terminal (+) of the solar panel 250 towards the rechargeable battery 210 and other peripheral devices represented by the load 480. In this case, current flows from ground through the body diode of the NFET 410 at the bottom of the solar panel into the negative terminal (-) of the solar panel 250. The body diode of the NFET 410 at the bottom of the solar panel causes a voltage drop of approximately 0.5 V (junction diode voltage), and the voltage at the bottom of the solar panel 408 is approximately -0.5 V. Conversely, when the solar panel 250 is not providing sufficient power, current flows from the rechargeable battery 210 into the positive terminal (+) of the solar panel 250. However, when the NFET 410 at the bottom of the solar panel is off, it does not allow current to flow from the drain (D) to the source (S). Therefore, the voltage 408 at the bottom of the solar panel is equal to the voltage of a rechargeable battery, which is a positive voltage, such as 2.5 V, 3.3 V, 4.2 V or 5 V.

[0114] In light of the above, it should be noted that when the solar panel 250 generates sufficient electrical energy, the NFET 410 at the bottom of the solar panel needs to be closed so that sufficient current can flow from the solar panel 250 to power the load 480 and / or charge the rechargeable battery 210. It should also be noted that to determine whether the solar panel 250 is generating sufficient electrical energy, the NFET 410 at the bottom of the solar panel needs to be open, and the voltage 408 at the bottom of the solar panel needs to be read. Figure 5 depicts a method 500 performed by a solar-powered asset tracker 300 to control the solar panel 250 to prevent the rechargeable battery 210 from being depleted by the solar panel 250 as discussed above.

[0115] The controller 230 of the solar-powered asset tracker 300 controls the NFET 410 at the bottom of the solar panel. Specifically, machine-executable programming instructions (i.e., "firmware") executed by the controller 230 cause the controller to open or close the switch at the bottom of the solar panel via a signal connected to the gate (G) of the NFET 410. Additionally, the machine-executable programming instructions executed by the controller 230 maintain tracking of the state of the NFET 410 at the bottom of the solar panel. Therefore, the solar-powered asset tracker 300 knows whether the solar panel 250 is connected to ground.

[0116] At step 502, if the solar panel 250 is connected to ground, control proceeds to step 504. If the solar panel 250 is not connected to ground, control proceeds to step 506.

[0117] At step 504, the solar-powered asset tracker 300 (executed via firmware by controller 230) disconnects the solar panel 250 from ground by disconnecting the NFET 410 at the bottom of the solar panel. This allows controller 230 to read the bottom voltage 408 of the solar panel from the bottom voltage sensor 405. Control then proceeds to step 506.

[0118] At step 506, the solar-powered asset tracker controller 230 reads the solar panel bottom voltage 408 from the solar panel bottom voltage sensor 405. As discussed above, the solar panel bottom voltage 408 indicates whether current is flowing from the solar panel 250 to peripheral devices and the rechargeable battery 210, or from the rechargeable battery 210 to the solar panel 250.

[0119] At step 508, the solar-powered asset tracker determines whether the solar panel 250 is generating sufficient electrical energy. The direction of current flow indicates whether the solar panel 250 is generating sufficient electrical energy. Specifically, a positive voltage value at the bottom voltage 408 of the solar panel indicates that current is flowing from the rechargeable battery 210 into the solar panel 250, therefore the solar panel 250 is not generating enough electrical energy to power the solar-powered asset tracker 300. In this case, the bottom NFET 410 of the solar panel remains off, and the solar panel 250 remains off.

[0120] At step 508, the negative voltage at the bottom of the solar panel indicates that current is flowing out from the positive terminal of the solar panel 250 and from ground through the body diode of the NFET 410 at the bottom of the solar panel into the negative terminal of the solar panel 250. This indicates that the solar panel 250 has generated sufficient electrical energy, and control returns to 510.

[0121] At step 510, the solar-powered asset tracker 300 connects the solar panel 250 to ground to allow the solar panel 250 to provide power to the load 480 and / or recharge the rechargeable battery 210.

[0122] Method 500 can be executed periodically to check the status of the solar panel 250 and disconnect it if necessary. This is indicated by the flow arrow between step 510 and step 502. Method 500 can also be used for other method calls to determine whether the solar panel 250 is generating enough electrical energy to power the various peripherals of the electronic device.

[0123] Advantageously, the above method allows the solar-powered asset tracker 300 to detect situations where the rechargeable battery 210 is depleted through the solar panel 250 due to the solar panel 250's inability to generate sufficient power. Furthermore, the above method provides a way to disconnect the solar panel 250 from the rechargeable battery 210 to prevent the rechargeable battery 210 from being depleted through the solar panel 250, thereby preventing degradation of the solar panel cells.

[0124] As discussed above, if the solar panel 250 is generating sufficient electrical energy and the NFET 410 at the bottom of the solar panel is off, the bottom voltage 408 of the solar panel presents a negative voltage value (e.g., -0.5 V). Conversely, when the solar panel 250 is not generating sufficient electrical energy, the bottom voltage 408 of the solar panel presents a positive voltage (e.g., 1.8 V, 3.3 V, 5 V, etc.). Since the bottom voltage 408 of the solar panel can have negative or positive values, such a signal cannot be provided to the analog-to-digital converter (ADC) built into the controller 230 to determine whether the solar panel 250 is generating sufficient electrical energy. Therefore, the bottom voltage sensor 405 of the solar panel is configured to convert the bottom voltage of the solar panel into a positive-only signal. Referring to FIG6, an implementation of the bottom voltage sensor 405 of the solar panel according to an embodiment of the present disclosure is shown.

[0125] In Figure 6, the solar panel bottom NFET 410 is implemented as an NFET. The solar panel bottom NFET 410 is connected at its gate to the solar panel switch enable signal (SLR_NFET_EN) via resistor R26. The solar panel switch enable signal is connected to the output pin of controller 230, allowing controller 230 to turn the solar panel bottom NFET 410 on or off. Another resistor R30 connects the gate of the solar panel bottom NFET 410 to ground. The solar panel bottom NFET 410 is connected to ground at its source (terminal 2) and to the solar panel bottom voltage sensor 405 at its drain.

[0126] The solar panel bottom voltage sensor 405 is implemented as an operational amplifier 602. The output 606 of the operational amplifier 602 is connected to its inverting input 603 and outputs the solar panel bottom voltage sensor signal (SLR_BOT_VSENSE). The non-inverting input 605 of the operational amplifier 602 is connected to ground. The positive power supply terminal 604 of the operational amplifier 602 is connected to the solar panel voltage sensor enable signal (SLR_BOT_VSENSE_EN). The negative power supply terminal 608 of the operational amplifier 602 is connected to the drain of the solar panel bottom NFET 410.

[0127] When the solar-powered asset tracker 300 needs to check the voltage 408 at the bottom of the solar panel, the firmware executed by the controller 230 invalidates the signal SLR_NFET_EN, thereby putting the bottom NFET 410 of the solar panel into off mode (i.e., the switch is off except through the conductivity of the body diode discussed above). With the bottom NFET 410 of the solar panel in off mode, the firmware executed by the controller 230 enables the signal SLR_BOT_VSENS_EN. At this time, the output signal SLR_BOT_VSENSE of the operational amplifier 602 of the bottom voltage sensor 405 of the solar panel outputs a positive analog signal indicating whether the solar panel 250 is generating electrical energy. When the bottom voltage 408 of the solar panel is positive, the output signal SLR_BOT_VSENSE takes a lower positive voltage value, while when the bottom voltage 408 of the solar panel is negative (i.e., -0.5 V as discussed above, due to the voltage drop between ground and the body diode of the bottom NFET 410 of the solar panel), the output signal SLR_BOT_VSENSE takes a higher positive voltage value. The output signal SLR_BOT_VESNSE of the voltage sensor 405 at the bottom of the solar panel is input to the ADC channel of the controller 230.

[0128] The controller 230 executes firmware that periodically enables the solar panel voltage sensor signal (SLR_BOT_VSENSE_EN) and uses its ADC channel to convert the solar panel bottom voltage sensor signal (SLR_BOT_VSENSE) into a digital value. This digital value determines whether the solar panel bottom voltage 408 is positive or negative. Therefore, in the case where the solar panel bottom NFET 410 is off and the solar-powered asset tracker 300 operates relying on the rechargeable battery 210, the solar-powered asset tracker 300 can also reconnect the solar panel 250 (by enabling the solar panel bottom NFET 410) when it determines that the solar panel 250 is generating power again. When it is known that the solar panel 250 is not generating enough power, the controller 230 disconnects the solar panel bottom NFET 410. In some implementations, the firmware executed by the controller 230 uses a periodic timer to periodically perform the aforementioned steps: enabling the solar panel voltage sensor (SLR_BOT_VSENSE_EN), switching the solar panel bottom voltage sensor signal (SLR_BOT_VSENSE), and comparing digital values ​​to determine whether the solar panel bottom voltage 408 is positive or negative.

[0129] Record the charging and discharging currents of the solar panel and battery.

[0130] Asset tracker 200 needs to monitor and record parameters related to the current generated by solar panel 250 and the charging / discharging current of rechargeable battery 210. Solar panel current sensor 415 is a current sensing device that provides a digital value indicating the current supplied by solar panel 250 at any given time. Rechargeable battery current sensor 425 indicates whether current is flowing into rechargeable battery 210 (during charging) or flowing out of rechargeable battery 210 (when solar panel 250 is not providing power and the system is therefore powered by rechargeable battery 210). The magnitudes of both the charging current (current flowing into rechargeable battery 210) and the discharging current (current flowing out of rechargeable battery 210) are provided to controller 230 and tracked for measurement and analysis.

[0131] Solar panel current sensor

[0132] In some implementations, the solar panel current sensor 415 is a current-sensing amplifier that includes a shunt resistor, an operational amplifier (“operational amplifier”) for increasing the voltage drop across the shunt resistor, and an ADC for converting the increased voltage drop into a digital value representing the current supplied by the solar panel 250. In some implementations, the ADC is part of the controller 230. In such cases, the solar panel current sensor may include a shunt resistor and an operational amplifier. In some implementations, the solar panel current sensor 415 is one of the following: a differential amplifier, a zero-drift amplifier, an instrumentation amplifier, a current-sensing ADC, a current-sensing transformer, a magnetic field sensor, and a transimpedance amplifier. In some embodiments, the solar panel current sensor 415 is an integrated circuit (IC), such as those from Text Instruments. TM The INA191 current sensing amplifier is used. As an example, Figure 7 illustrates an implementation of a solar panel current sensor 700 as a current sensing amplifier 710, which is an INA191 current sensing amplifier. A shunt resistor R1 is connected to a signal line connected to the positive terminal of the solar panel 250. The current sensing amplifier 710 measures the current flowing in the shunt resistor R1 via resistors R2 and R3 through its two input terminals IN+ and IN-, respectively. The output pin (OUT) of the current sensing amplifier 710 provides an indication of the current output by the solar panel 250 as the signal SLR_ISENSE. The current sensing amplifier 710 is enabled by a solar panel current sensor enable signal (ISENSE_EN), which is connected to the enable (EN) pin of the current sensing amplifier 710.

[0133] During operation, when the controller 230 executes a machine-executable programming instruction to enable the solar panel current sensor signal ISENSE_EN, the current sensing amplifier 710 outputs a voltage indicating the solar panel current on the solar panel current sensor signal SLR_ISENSE. The solar panel current sensing signal SLR_ISENSE can be input to the ADC channel of the controller 230, so that the solar panel current sensing signal SLR_ISENSE is converted into a digital value representing the solar panel current supplied by the solar panel 250.

[0134] The digital value representing the current supplied by solar panel 250 can be transmitted from solar-powered asset tracker 300 to asset tracking server 130 via network interface 220. This digital value representing the current supplied by solar panel 250 can be analyzed and / or correlated with other data.

[0135] Rechargeable battery charging and discharging sensor

[0136] The solar-powered asset tracker 300 also needs to determine whether the rechargeable battery 210 is being charged by the solar panel 250 or discharging while powering components of the solar-powered asset tracker 300. The magnitude of both the rechargeable battery charging current and the rechargeable battery discharging current also help determine metrics such as the charging and discharging rates of the rechargeable battery 210. The solar-powered asset tracker 300 has a rechargeable battery current sensor 425 connected (via a top battery switch 420) to the positive terminal of the rechargeable battery 210.

[0137] Figure 8 illustrates a bidirectional current sensor 800 according to an embodiment of the present disclosure, which is an implementation of a rechargeable battery current sensor 425. The bidirectional current sensor 800 includes two reverse-coupled current sensors for measuring the rechargeable battery current in both the charging and discharging directions. The charging direction is when current is flowing from the solar panel 250 to the rechargeable battery 210. The discharging direction is when current is flowing from the rechargeable battery 210 to the solar panel 250. In the depicted implementation, the charging current is measured by a charging current sensing amplifier 810, and the discharging current is measured by a discharging current sensing amplifier 820. Each of the charging current sensing amplifier 810 and the discharging current sensing amplifier 820 can be implemented by an INA191 current sensing amplifier. A shunt resistor R8 is connected to the rechargeable battery 210 via a top battery switch 420.

[0138] When current flows through the shunt resistor R8 in the charging direction and the charging current sensing amplifier enable signal ISENSE_EN is enabled, the charging current sensing amplifier 810 measures the rechargeable battery charging current and provides the rechargeable battery charging current signal BAT_CHRG_ISENSE, which is an analog voltage that can be converted by the ADC into a value representing the rechargeable battery charging current.

[0139] When current flows through the shunt resistor R8 in the discharge direction and the discharge current sensing amplifier enable signal ISENSE_EN is enabled, the discharge current sensing amplifier 820 measures the rechargeable battery discharge current and provides the rechargeable battery discharge current signal BAT_DSCHRG_ISENSE, which is an analog voltage that can be converted by the ADC into a value representing the rechargeable battery charging current.

[0140] The controller 230 may have a built-in ADC that converts both the rechargeable battery charging current signal and the rechargeable battery discharging current signal into digital values. The rechargeable battery charging current value and the rechargeable battery discharging current value can be transmitted via network interface 220 through network 50 to the asset tracking server 130 for recording and analysis. For example, the rechargeable battery charging current can be used to determine how many minutes or hours are needed for the rechargeable battery 210 to become fully charged.

[0141] Unregulated voltage sensing

[0142] The bus connecting the solar panel 250, the rechargeable battery 210, and all peripheral devices represented by the load 480 is called the “unregulated voltage bus” 488 because the voltage on such a bus can vary. The voltage of the unregulated voltage bus 488 is measured by the unregulated voltage sensor 435. The voltage measured by the unregulated voltage sensor 435 will depend on whether the rechargeable battery 210 is connected to the unregulated voltage bus 488. As can be seen in Figure 4, the rechargeable battery 210 can be connected to the unregulated voltage bus 488 at its positive terminal by closing the top battery switch 420 (and closing the bottom battery switch 430 to close the circuit and connect the negative terminal of the rechargeable battery 210 to ground). Similarly, the solar panel 250 is connected to the unregulated voltage bus 488 at its positive terminal (via the solar panel current sensor 415). Therefore, both the solar panel 250 and the rechargeable battery 210 are connected to the controller 230 and multiple peripheral devices via the unregulated voltage bus 488 at their respective positive terminals.

[0143] When both the top battery switch 420 and the bottom battery switch 430 are closed, the rechargeable battery 210 is connected to the unregulated voltage bus 488. When both the rechargeable battery 210 and the solar panel 250 are connected to the unregulated voltage bus 488, the unregulated voltage sensor 435 measures the battery voltage of the rechargeable battery 210. The solar panel 250 is considered a current source, and its voltage varies with the intensity of solar radiation incident on it. For example, solar radiation changes from sunny to partially cloudy, and then back to mostly cloudy. Other weather conditions and events, such as fog, smoke from forest fires, and dust storms, also affect the solar panel voltage.

[0144] When the top battery switch 420 and the bottom battery switch 430 are open, the rechargeable battery 210 is disconnected from the unregulated voltage bus 488. When the rechargeable battery 210 is disconnected from the unregulated voltage bus 488, the unregulated voltage sensor 435 measures the solar panel voltage at the positive terminal of the solar panel 250.

[0145] In some embodiments, the top battery switch 420 or the bottom battery switch 430 is one of the following: a bipolar junction transistor (BJT) switch, a relay, a solid-state relay (SSR), an integrated circuit (IC) switch, and an optocoupler. If MOSFET technology is to be used, the top battery switch 420 is a PFET, and the bottom battery switch is an NFET, due to the presence of a body diode when the NFET or PFET is turned off. This embodiment will now be described with reference to FIG10.

[0146] Prevent unnecessary discharge / charge

[0147] As discussed above, it is desirable to reduce the charge / discharge cycles of the rechargeable battery 210 to extend its lifespan. For this reason, the power management subsystem 400 disconnects the rechargeable battery 210 from the load 480 when two conditions are met. The first condition is that the solar panel 250 is generating sufficient electrical energy to power the load 480. The second condition is that the rechargeable battery 210 is fully charged. As discussed, the first condition is determined by the voltage sensor 405 at the bottom of the solar panel. In this case, current flows from the solar panel 250 to the rechargeable battery 210, thus charging the battery. The second condition is when the voltage of the rechargeable battery 210 reaches the maximum battery voltage indicating that the rechargeable battery 210 is fully charged. Specifically, a fully charged rechargeable battery will have the maximum battery voltage measured at its terminals. For example, a fully charged 4.2 V lithium-ion battery will have 4.2 V across its positive and negative terminals. Once the battery loses some of its charge, the voltage between its positive and negative terminals drops.

[0148] When the battery voltage rises and reaches the maximum battery voltage threshold, this indicates that the rechargeable battery 210 is fully charged. The unregulated voltage sensor 435 outputs an unregulated voltage signal reflecting the rechargeable battery voltage to the controller 230. The unregulated voltage sensor output is an analog voltage indicating the voltage on the unregulated voltage bus 488. The controller 230 can compare the rechargeable battery voltage with the maximum battery voltage. If the rechargeable battery voltage reaches the maximum battery voltage, the controller 230 determines that the rechargeable battery 210 is fully charged. In response to determining that the rechargeable battery 210 is fully charged, and knowing (from the voltage sensor 405 at the bottom of the solar panel) that the solar panel 250 is generating sufficient power to power peripheral devices, the controller 230 disconnects the rechargeable battery 210 from the peripheral devices. Specifically, the controller 230 outputs a control signal to disconnect the top battery switch 420 and the bottom battery switch 430. Advantageously, the rechargeable battery 210 is not unnecessarily discharged and recharged, and the lifespan of the rechargeable battery 210 is extended.

[0149] Figure 9 illustrates a simplified implementation of the top battery switch 420 and the bottom battery switch 430 according to an embodiment of the present disclosure.

[0150] In the depicted embodiment, the top battery switch 420 includes a PFET Q3 with a 1M resistor R17 connected between its gate and source. The gate of PFET Q3 is connected to the drain of an NFET Q4, the source of PFET Q3 is connected to the positive terminal of the rechargeable battery 210, and the drain of PFET Q3 is connected to an unregulated voltage bus 488. The gate of NFET Q4 is connected via a 1K resistor R18 to a top battery switch control signal named BAT_PFEN_EN. The gate of NFET Q4 is also connected to ground via a 1M resistor R19. When the top battery switch control signal BAT_PFEN_EN is deactivated, NFET Q4 is off. No current flows through Q4, so the voltage at the gate of Q3 is equal to the voltage at the source of Q3. Since Vsg of Q3 is 0, Q3 is off. When the top battery switch control signal BAT_PFET_EN is enabled, Q4 turns on, and current flows from the positive terminal of rechargeable battery 210 through R17 and then through Q4. The current through R17 causes a voltage drop, making Vsg of Q3 greater than the threshold voltage of Q3, and Q3 turns on, thereby connecting the positive terminal of rechargeable battery 210 to the unregulated voltage bus 488.

[0151] The bottom battery switch 430 is implemented as an NFET Q6, with its drain connected to the negative terminal of the rechargeable battery 210 and its source connected to ground. The bottom battery switch control signal BAT_NFET_EN is connected to the gate of Q6 via a 1K resistor R23, and the gate of Q3 is connected to ground via a 1M resistor R24. When the bottom battery switch control signal BAT_NFET_EN is deactivated, Q6 is off, and the negative terminal of the rechargeable battery 210 is not connected to ground. Conversely, when the bottom battery switch control signal BAT_NFET_EN is activated, current flows through R23 and then through R24 to ground. The voltage drop across R23 causes Vgs of Q6 to exceed the threshold voltage, and Q6 turns on, thereby connecting the negative terminal of the rechargeable battery 210 to ground.

[0152] It should be noted that when in cutoff mode, both PFET Q3 and NFET Q4 have body diodes, but since Q3 is a PFET and Q4 is an NFET, their respective body diodes conduct current in opposite directions. Therefore, when both BAT_PFET_EN and BAT_NFET_EN are set to invalid, Q3 and Q4 are cut off, and no current flows to or from the rechargeable battery 210.

[0153] Addressing undervoltage caused by decreased solar radiation

[0154] As discussed above, when the rechargeable battery 210 is fully charged and the solar panel 250 is able to power the system, the rechargeable battery 210 can be disconnected from the unregulated voltage bus 488 (and thus from the rest of the system). In such a situation, if the solar panel 250 is no longer able to provide sufficient power to power the load 480, there is a risk of undervoltage.

[0155] When the rechargeable battery 210 is disconnected from the unregulated voltage bus 488, the unregulated voltage sensor 435 compares the solar panel voltage to an undervoltage threshold. For example, it may be known that some peripherals in the asset tracker's peripherals do not operate when the supply voltage is below 3.5 V. In response to the solar panel voltage (i.e., the voltage of the unregulated voltage bus 488) reaching or falling below the undervoltage threshold, the unregulated voltage sensor 435 signals the controller 230 that the solar panel voltage is too low for the operation of the solar-powered asset tracker 300. Upon receiving the signal indicating that the solar panel voltage has reached the undervoltage threshold, the controller 230 closes both the top battery switch 420 and the bottom battery switch 430, thereby connecting the rechargeable battery 210. Advantageously, connecting the rechargeable battery 210 back prevents an undervoltage condition that could occur when the solar panel 250 does not receive sufficient solar radiation to generate enough current to power the asset tracker's peripherals.

[0156] When switching between solar panel 250 and rechargeable battery 210, a momentary drop in voltage may occur on unregulated voltage bus 488. A large-capacity capacitor 440 remedies this situation. The large-capacity capacitor 440 is charged from either solar panel 250 or rechargeable battery 210, and in the event of a momentary drop (undervoltage), the large-capacity capacitor 440 discharges into unregulated voltage bus 488, thereby maintaining unregulated voltage bus 488 at a voltage level above the undervoltage threshold.

[0157] Advantageously, when the solar panel 250 enables the electronic device (i.e., the solar-powered asset tracker 300) to operate, the rechargeable battery 210 is not connected. In this case, the rechargeable battery 210 is not unnecessarily discharged and recharged, especially when the rechargeable battery 210 is already fully charged. The discharge / recharge cycles of the rechargeable battery 210 are reduced, thereby extending the life of the rechargeable battery 210. Conversely, when the solar panel 250 is unable to supply sufficient current to drive all the necessary peripheral equipment used in the intended operation, the rechargeable battery 210 is connected to prevent undervoltage conditions.

[0158] Troubleshooting rechargeable battery problems

[0159] Another problem mitigated by this disclosure is the issue of rechargeable battery failure. The rechargeable battery 210 has a specific lifespan, and when it reaches the end of that lifespan, the voltage supplied by the rechargeable battery drops below the minimum voltage threshold required for the operation of the peripheral devices of the solar-powered asset tracker 300. When this occurs, the solar-powered asset tracker 300 checks whether the solar panel 250 can power the solar-powered asset tracker 300. If the solar panel 250 can power the solar-powered asset tracker 300 (as determined by the solar panel bottom voltage 408), the solar panel bottom NFET 410 is closed to connect the solar panel 250 to ground, thereby allowing the solar panel 250 to efficiently power the load 480. If the solar panel 250 cannot power the solar-powered asset tracker, the solar-powered asset tracker is turned off until the solar panel 250 has sufficient radiation to generate enough electrical energy to power the system. Referring to Figure 4, when the solar panel 250 generates sufficient electrical energy, current flows through the body diode of the NFET 410 at the bottom of the solar panel into the negative terminal of the solar panel 250 and flows out from the positive terminal of the solar panel 250 to the load 480. The current activates the controller 230, which checks the voltage 408 at the bottom of the solar panel. In response to the detection of the voltage 408 at the bottom of the solar panel indicating that the solar panel 250 is generating electrical energy, the controller 230 activates (i.e., closes) the NFET 410 at the bottom of the solar panel, thereby allowing the solar-powered asset tracker 300 to operate relying on the solar panel 250 and sending a notification about a faulty battery to the asset tracking server 130.

[0160] Figure 10 illustrates a method 1000 for controlling a solar-powered electronic device powered by a solar panel and a rechargeable battery, the solar panel and the rechargeable battery being connected to an unregulated voltage bus 488 as depicted in Figure 4.

[0161] At step 1010, the electronic device reads the voltage of the unregulated voltage bus. For example, controller 230 may execute firmware machine-executable programming instructions that enable unregulated voltage sensor 435. The output of unregulated voltage sensor 435 is an analog voltage representing the voltage of the unregulated voltage bus. Referring to FIG11, an exemplary unregulated voltage sensor according to an embodiment of the present invention is shown. The depicted unregulated voltage sensor includes operational amplifier U43 in a voltage follower arrangement. The inverting input of operational amplifier U43 comes from the center of a voltage divider connected to unregulated voltage bus 488 via PFET switch Q2. As shown, the voltage divider includes resistors R13 and R15. The output of operational amplifier U43 is an analog signal representing the voltage (VUNREG_VSENSE) of unregulated voltage bus 488. Controller 230 may enable the unregulated voltage sensor via an unregulated voltage sensor enable signal VUNREG_VSENSE_EN. The unregulated voltage sensor enable signal VRUNEG_VENSE_EN is input to the gate of NFET switch Q1, which is connected to the gate of PFET Q2 at its drain and connected to the unregulated voltage bus 488 via resistor R4.

[0162] When the unregulated voltage sensor enable signal VRUNEG_VENSE_EN is disabled, Vgs of Q1 is 0 V, and Q2 is off. Since no current flows through Q1, no current flows through R4. The voltage at the gate of Q2 is higher than the voltage at its source. Vsg is less than the threshold voltage. Therefore, Q2 is off, and the inverting input of operational amplifier U43 is not connected to the unregulated voltage bus 488.

[0163] When the unregulated voltage sensor enable signal VRUNEG_VENSE_EN is active, current flows through R11, causing the voltage Vgs to exceed the threshold voltage of NFET Q1. NFET Q1 turns on, causing current to flow through R4, and the voltage at the gate of Q2 becomes 0 V. Therefore, Vsg of Q2 is greater than the threshold voltage of the PFET. Current flows through Q1, R13, and R15. The inverting input of U43 is a voltage representing the voltage drop across R15, which is proportional to the unregulated voltage bus 488.

[0164] The output of the unregulated voltage sensor is input to a dedicated ADC or an ADC channel of the ADC built into the controller 230. The firmware of the solar-powered electronics can determine the voltage of the unregulated voltage bus.

[0165] Returning to Figure 10, at step 1020, the electronics determine whether the rechargeable battery 210 is connected to the unregulated voltage bus 488. In other words, the electronics determine whether at least one switch between the rechargeable battery 210 and the unregulated voltage bus 488 is open or closed. When at least one switch between the rechargeable battery 210 and the unregulated voltage bus is closed, control proceeds to step 1030. If at least one switch between the rechargeable battery 210 and the unregulated voltage bus 488 is open, control proceeds to step 1040. In some implementations, as discussed above, at least one switch includes a top battery switch 420 and / or a bottom battery switch 430.

[0166] At step 1030, the electronic device has determined that the rechargeable battery 210 is connected to the unregulated voltage bus 488. In this case, the electronic device infers that the voltage of the unregulated voltage bus 488 represents the battery voltage of the rechargeable battery 210. At step 1030, the electronic device checks whether the battery voltage indicates that the rechargeable battery 210 is fully charged, that is, whether the battery voltage has reached the maximum battery voltage threshold indicating a full charge. If the battery voltage indicates that the rechargeable battery 210 is fully charged, control proceeds to step 1050. If the battery voltage indicates that the rechargeable battery 210 is not fully charged, control proceeds to step 1070.

[0167] At step 1050, the electronic device has determined that the rechargeable battery 210 is fully charged. However, before disconnecting the battery, the electronic device first determines whether the solar panel 250 can power the electronic device. Therefore, at step 1050, the electronic device executes method 500 of FIG. 5, which includes reading the voltage 408 at the bottom of the solar panel and determining whether the solar panel 250 is generating sufficient electrical energy. At step 1055, if the solar panel 250 is providing sufficient electrical energy to power the electronic device, control proceeds to step 1058. If the solar panel 250 is not providing sufficient electrical energy, control returns to step 1010.

[0168] At step 1058, the electronics disconnect the rechargeable battery from the unregulated voltage bus, for example, by disconnecting the switch between them. For example, the electronics may invalidate the top battery switch control signal BAT_PFET_EN and the bottom battery switch control signal BAT_NFET_EN. The top battery switch 420 and the bottom battery switch 430 are turned off, and the rechargeable battery 210 is isolated from the load 480. The load 480 is powered only by the solar panel 250. Discharging / recharging of the rechargeable battery 210 is stopped, thereby extending the lifespan of the rechargeable battery 210. After this, control returns to step 1010.

[0169] At step 1070, the rechargeable battery 210 is not fully charged. The electronics check whether the voltage of the unregulated voltage bus 488 indicates that the rechargeable battery 210 may be defective. A battery is defective when the voltage drops to a defective voltage threshold. As an example, when the battery voltage is 3.5 V, the battery may be at full capacity, while when the battery voltage is 2.5 V, the battery may be at minimum capacity. If the battery drops below 2.5 V, for example, to 2.0 V, this may indicate that the battery is degraded and may not be able to recharge back to its full capacity, or it may take a long time to recharge back to its full capacity. In such a case, it is recommended to send a notification indicating that the battery may need to be replaced or that the electronics need to be replaced (if the battery is not removable). If the rechargeable battery 210 is determined to be defective based on the measured voltage of the unregulated voltage bus 488, control proceeds to step 1075. If the battery is not defective, control returns to step 1010. One way to determine a defective battery condition is by comparing the voltage of the unregulated voltage bus to a defective voltage threshold. This can be accomplished via firmware executed by the controller of the electronic device (e.g., controller 230).

[0170] At step 1075, the electronic device checks whether the solar panel 250 can provide sufficient power to perform a communication action. Specifically, the electronic device checks whether the solar panel 250 can power the network interface 220 to send a notification message to a remote server (e.g., asset tracking server 130). When the solar panel 250 can provide sufficient power to power the network interface, control proceeds to step 1080. When the solar panel 250 cannot provide sufficient power to power the network interface 220, the electronic device waits in step 1075. If the circuit implementation of Figure 6 is used, when the solar panel 250 can provide sufficient power, the controller can detect this based on the voltage 408 at the bottom of the solar panel and proceed to step 1080.

[0171] At step 1080, the electronic device powers on the network interface 220 and sends a notification to the remote server indicating that the rechargeable battery 210 of the electronic device needs to be replaced. Control then returns to step 1010.

[0172] At step 1040, the electronic device determines that the rechargeable battery 210 is disconnected from the unregulated voltage bus 488. The electronic device knows the state of at least one switch (e.g., top battery switch 420 and bottom battery switch 430) between the rechargeable battery 210 and the unregulated voltage bus 488 because this switch operates under the control of the electronic device, for example, via firmware executed by the controller 230 of the electronic device. Since the rechargeable battery 210 is disconnected from the unregulated voltage bus 488, the voltage of the unregulated voltage bus 488 represents the voltage supplied by the solar panel 250, such as that applied to the peripheral devices of the electronic device (i.e., the load 480 and the controller 230). The electronic device determines a minimum unregulated voltage bus voltage below which some peripheral devices may not function correctly or may not function correctly at all. This minimum unregulated voltage bus voltage may be referred to as the undervoltage voltage or undervoltage threshold. If the voltage of the unregulated voltage bus 488 is at or below the undervoltage threshold, the electronic device determines a potential undervoltage condition, and control proceeds to step 1060. If the voltage of the unregulated voltage bus is above the undervoltage threshold, control returns to step 1010.

[0173] At step 1060, the electronic device connects the rechargeable battery 210 to the unregulated voltage bus 488 to prevent undervoltage conditions. For example, the controller 230 enables the top battery switch control signal BAT_PFET_EN and the bottom battery switch control signal BAT_NFET_EN to enable both the top battery switch 420 and the bottom battery switch, respectively. The electronic device can also perform step 1060 in response to the drop threshold detector 445 detecting that the voltage of the unregulated voltage bus has dropped below the minimum unregulated voltage bus when the rechargeable battery 210 is disconnected from the unregulated voltage bus 488 (i.e., after performing step 1058). In response to detecting that the voltage of the unregulated bus 488 has dropped below the minimum unregulated voltage bus, the drop threshold detector 445 sets an interrupt line to the controller 230, which in turn triggers an interrupt event. In response to the interrupt event, the controller 230 executes firmware instructions that perform step 1060 of connecting the rechargeable battery 210 to the unregulated voltage bus 488.

[0174] At step 1064, the electronic device executes method 500 as described above with reference to FIG5. In this method, the electronic device determines whether to connect the solar panel 250 based on whether the solar panel 250 can generate sufficient electrical energy. As discussed above, method 500 is executed periodically by the electronic device to determine whether the solar panel 250 should be disconnected from ground to prevent the rechargeable battery 210 from being depleted through the solar panel 250.

[0175] Implementations of the technology in circuit systems and / or computer-executable instructions have been described. It should be understood that some implementations may take the form of methods or processes, and at least one example of such methods or processes has been provided. Actions performed as part of a method or process can be ordered in any suitable manner. Therefore, implementations can be constructed that perform actions in an order different from the order shown, which may include performing some actions simultaneously, even if they are shown as sequential actions in the illustrative embodiments. Various aspects of the above-described embodiments can be used individually, in combination, or in various arrangements not specifically discussed in the embodiments described above, and are therefore not limited in their application to the details and arrangements of the components set forth in the above description or shown in the accompanying drawings. For example, aspects described in one embodiment can be combined in any way with aspects described in other embodiments.

Claims

1. A method in an electronic device, the electronic device comprising a power management subsystem, a controller, and a plurality of peripheral devices, the electronic device being powered by a solar panel and a rechargeable battery, both the solar panel and the rechargeable battery being connected at their respective positive terminals to the controller and the plurality of peripheral devices, the method comprising: Determine whether the solar panel is connected to the ground terminal at its negative terminal; In response to determining that the solar panel is connected to the grounding terminal at its negative terminal, the negative terminal is disconnected from the grounding terminal; the voltage at the negative terminal of the solar panel is read. And in response to determining, based on the voltage, that the solar panel is generating sufficient electrical energy to power at least some of the plurality of peripheral devices: connecting the negative terminal of the solar panel to the grounding terminal.

2. The method according to claim 1, further comprising: In response to determining, based on the voltage, that the solar panel does not generate sufficient electrical energy to power at least some of the plurality of peripheral devices, the negative terminal of the solar panel remains disconnected from the grounding terminal.

3. The method according to claim 1 or claim 2, wherein: The negative terminal of the solar panel is connected to the ground terminal via an N-channel field-effect transistor (NFET) switch having a source, a gate, and a drain; the NFET switch is connected to the ground terminal at its source and to the negative terminal of the solar panel at its drain; and determining that the solar panel is generating sufficient energy includes detecting a negative voltage at the drain of the NFET switch.

4. The method according to any one of claims 1 to 3, wherein: The negative terminal of the solar panel is connected to the ground terminal via a P-channel field-effect transistor (PFET) switch having a source, a gate, and a drain; the PFET switch is connected to the ground terminal at its drain and to the negative terminal of the solar panel at its source; and determining that the solar panel is generating sufficient energy includes detecting a negative voltage at the source of the PFET switch.

5. The method according to any one of claims 2 to 4, wherein: The negative terminal of the solar panel is connected to the ground terminal via an N-channel field-effect transistor (NFET) switch having a source, a gate, and a drain; the NFET switch is connected to the ground terminal at its source and to the negative terminal of the solar panel at its drain; and determining that the solar panel is not generating sufficient energy includes detecting a positive voltage at the drain of the NFET switch.

6. The method according to any one of claims 2 to 5, wherein: The negative terminal of the solar panel is connected to the ground terminal via a P-channel field-effect transistor (PFET) switch having a source, a gate, and a drain; the PFET switch is connected to the ground terminal at its drain and to the negative terminal of the solar panel at its source; and determining that the solar panel is not generating sufficient energy includes detecting a positive voltage at the source of the PFET switch.

7. The method according to any one of claims 1 to 6, wherein: The negative terminal of the solar panel is connected to the ground terminal via a field-effect transistor (FET) switch; and connecting the negative terminal to the ground terminal includes closing the FET switch.

8. The method according to any one of claims 1 to 7, wherein, Reading the voltage at the negative terminal of the solar panel includes: activating a voltage sensor connected to the negative terminal of the solar panel; and reading the voltage sensor signal of the voltage sensor.

9. The method according to claim 8, wherein: The voltage sensor includes an operational amplifier having an inverting input, a non-inverting input, a positive power supply terminal, a negative power supply terminal, and an output terminal; the negative power supply terminal is connected to the negative terminal of the solar panel; the output terminal of the operational amplifier is connected to the inverting input terminal; the voltage sensor signal of the voltage sensor is the output of the operational amplifier; the non-inverting input terminal of the operational amplifier is connected to ground; and enabling the voltage sensor includes the controller activating the signal connected to the positive power supply terminal of the operational amplifier.

10. The method according to claim 8 or claim 9, wherein: The voltage sensor signal of the voltage sensor includes a positive analog signal; and reading the voltage sensor signal of the voltage sensor includes converting the positive analog signal into a digital value.

11. An electronic device comprising a controller; a memory coupled to the controller; and a plurality of peripheral devices; A solar panel coupled to the controller, the memory, and the plurality of peripheral devices; A rechargeable battery coupled to the controller, the memory, the plurality of peripheral devices, and the solar panel; A power management subsystem coupled to the solar panel and the rechargeable battery, the power management subsystem including a voltage sensor connected to the negative terminal of the solar panel and a bottom switch of the solar panel connected to the negative terminal of the solar panel; a memory storing machine-executable programming instructions configuring the electronic device to: determine whether the solar panel is connected to a ground terminal via the bottom switch of the solar panel at its negative terminal; and disconnect the negative terminal from the ground terminal in response to determining that the solar panel is connected to the ground terminal at its negative terminal; Read the voltage at the negative terminal of the solar panel; In response to determining, based on the voltage, that the solar panel is generating sufficient electrical energy to power at least some of the plurality of peripheral devices, the negative terminal of the solar panel is connected to the grounding terminal.

12. The electronic device according to claim 11, wherein, The machine-executable programming instructions also configure the electronic device to: read the voltage at the negative terminal of the solar panel; and in response to determining based on the voltage that the solar panel does not generate enough electrical energy to power at least some of the plurality of peripheral devices: keep the negative terminal of the solar panel disconnected from the ground terminal.

13. The electronic device according to claim 11 or claim 12, wherein: The solar panel bottom switch includes an N-channel field-effect transistor (NFET) switch having a source, a gate, and a drain; the NFET switch is connected at its source to the ground terminal and at its drain to the negative terminal of the solar panel; and machine-executable programming instructions configuring the electronic device to determine that the solar panel is generating sufficient energy include machine-executable programming instructions for detecting a negative voltage at the drain of the NFET switch.

14. The electronic device according to any one of claims 11 to 13, wherein: The bottom switch of the solar panel includes a P-channel field-effect transistor (PFET) switch having a source, a gate, and a drain. The PFET switch is connected at its drain to the ground terminal and at its source to the negative terminal of the solar panel; and the machine-executable programming instructions for determining that the solar panel is generating sufficient energy include machine-executable programming instructions that configure the electronic device to detect the negative voltage at the source of the PFET switch.

15. The electronic device according to any one of claims 12 to 14, wherein: The solar panel bottom switch includes an N-channel field-effect transistor (NFET) switch having a source, a gate, and a drain; the NFET switch is connected at its source to the ground terminal and at its drain to the negative terminal of the solar panel; and machine-executable programming instructions configuring the electronic device to determine that the solar panel is not generating sufficient energy include machine-executable programming instructions configuring the electronic device to detect a positive voltage at the drain of the NFET switch.

16. The electronic device according to any one of claims 12 to 15, wherein: The bottom switch of the solar panel includes a P-channel field-effect transistor (PFET) switch having a source, a gate, and a drain. The PFET switch is connected at its drain to the ground terminal and at its source to the negative terminal of the solar panel; and the machine-executable programming instructions for determining that the solar panel is not generating sufficient energy include machine-executable programming instructions that configure the electronic device to detect the positive voltage at the source of the PFET switch.

17. The electronic device according to any one of claims 11 to 16, wherein: The solar panel bottom switch includes a field-effect transistor (FET) switch; and the machine-executable programming instructions that configure the electronic device to connect the negative terminal to the ground terminal include machine-executable programming instructions for closing the FET switch.

18. The electronic device according to any one of claims 11 to 17, wherein, Machine-executable programming instructions that configure the electronic device to read the voltage at the negative terminal of the solar panel include machine-executable programming instructions that configure the electronic device to perform the following operations: activate the voltage sensor; and read the voltage sensor signal of the voltage sensor.

19. The electronic device according to claim 18, wherein: The voltage sensor includes an operational amplifier having an inverting input, a non-inverting input, a positive power supply terminal, a negative power supply terminal, and an output terminal; the negative power supply terminal is connected to the negative terminal of the solar panel; the output terminal of the operational amplifier is connected to the inverting input terminal of the operational amplifier; the voltage sensor signal of the voltage sensor is the output of the operational amplifier; the non-inverting input terminal of the operational amplifier is connected to ground; and machine-executable programming instructions for configuring the electronic device to enable the voltage sensor include machine-executable programming instructions for configuring the electronic device to have the signal connected to the positive power supply terminal of the operational amplifier set to valid by the controller.

20. The electronic device according to claim 18 or claim 19, wherein: The voltage sensor signal of the voltage sensor includes a positive analog signal; and the machine-executable programming instructions that configure the electronic device to read the voltage sensor signal of the voltage sensor include machine-executable programming instructions that configure the electronic device to convert the positive analog signal into a digital value.

21. A method in an electronic device, the electronic device including a power management subsystem, a controller, and a plurality of peripheral devices, the electronic device being powered by a solar panel and a rechargeable battery, both the solar panel and the rechargeable battery being connected to the controller and the plurality of peripheral devices via an unregulated voltage bus at their respective positive terminals, the method comprising: Read the voltage of the unregulated voltage bus; And in response to determining that the rechargeable battery is connected to the unregulated voltage bus: in response to determining that the rechargeable battery is fully charged based on the voltage of the unregulated voltage bus: in response to determining that the solar panel provides sufficient electrical energy, disconnecting the rechargeable battery from the unregulated voltage bus; wherein the solar panel provides sufficient electrical energy when current flows from the solar panel to the rechargeable battery.

22. The method according to claim 21, wherein, Determining that the solar panel provides sufficient electrical energy includes: disconnecting the negative terminal of the solar panel from the grounding terminal; and detecting the negative voltage at the negative terminal of the solar panel using a voltage sensor.

23. The method according to claim 22, wherein: The voltage sensor includes an operational amplifier having an inverting input, a non-inverting input, a positive power supply terminal, a negative power supply terminal, and an output terminal; the negative power supply terminal is connected to the negative terminal of the solar panel; the output terminal of the operational amplifier is connected to the inverting input terminal; the voltage sensor signal of the voltage sensor is the output of the operational amplifier; the non-inverting input terminal of the operational amplifier is connected to ground; and enabling the voltage sensor includes the controller activating the signal connected to the positive power supply terminal of the operational amplifier.

24. The method according to claim 23, wherein: The voltage sensor signal of the voltage sensor includes a positive analog signal; and reading the voltage sensor signal of the voltage sensor includes converting the positive analog signal into a digital value.

25. The method according to any one of claims 21 to 24, wherein: The negative terminal of the solar panel is connected to a ground terminal via an N-channel field-effect transistor (NFET) switch having a source, a gate, and a drain; the NFET switch is connected to the ground terminal at its source and to the negative terminal of the solar panel at its drain; and determining that the solar panel is generating sufficient energy includes detecting a negative voltage at the drain of the NFET switch.

26. The method according to any one of claims 21 to 25, wherein, Disconnecting the rechargeable battery from the unregulated voltage bus includes: disconnecting the top battery switch between the positive terminal of the rechargeable battery and the unregulated voltage bus; and disconnecting the bottom battery switch between the negative terminal of the rechargeable battery and the ground terminal.

27. The method according to any one of claims 21 to 26, further comprising: In response to determining that the rechargeable battery is connected to the unregulated voltage bus: in response to determining that the rechargeable battery is defective based on the voltage of the unregulated voltage bus: in response to determining that the solar panel provides sufficient power to power the network interface of the electronic device, powering the network interface and sending a notification to a remote server indicating that the rechargeable battery is defective.

28. The method according to any one of claims 21 to 27, further comprising: In response to determining that the rechargeable battery is disconnected from the unregulated voltage bus: in response to determining a potential undervoltage condition based on the voltage of the unregulated voltage bus: connect the rechargeable battery to the unregulated voltage bus.

29. The method of claim 28, further comprising: In response to determining that the rechargeable battery is disconnected from the unregulated voltage bus: in response to determining a potential undervoltage condition based on the voltage of the unregulated voltage bus: in response to determining that the solar panel is not generating sufficient electrical energy, disconnect the solar panel from the ground terminal at its negative terminal.

30. The method according to claim 29, wherein: The negative terminal of the solar panel is connected to the ground terminal via an N-channel field-effect transistor (NFET) switch having a source, a gate, and a drain; the NFET switch is connected to the ground terminal at its source and to the negative terminal of the solar panel at its drain; and determining that the solar panel is not generating sufficient energy includes detecting a positive voltage at the drain of the NFET switch.

31. An electronic device comprising: Controller; A memory coupled to the controller; Multiple peripheral devices coupled to the controller; Unregulated voltage bus; A rechargeable battery for providing power to the controller, the memory, and the plurality of peripheral devices via the unregulated voltage bus; a solar panel for recharging the rechargeable battery and for providing power to the controller, the memory, and the plurality of peripheral devices via the unregulated voltage bus; A power management subsystem coupled to the controller, the rechargeable battery, and the solar panel; the memory stores machine-executable programming instructions that, when executed by the controller, configure the electronic device to read the voltage of the unregulated voltage bus; And in response to determining that the rechargeable battery is connected to the unregulated voltage bus: in response to determining that the rechargeable battery is fully charged based on the voltage of the unregulated voltage bus: in response to determining that the solar panel provides sufficient electrical energy, disconnecting the rechargeable battery from the unregulated voltage bus; wherein the solar panel provides sufficient electrical energy when current flows from the solar panel to the rechargeable battery.

32. The electronic device according to claim 31, wherein, Machine-executable programming instructions that configure the electronic device to determine that the solar panel provides sufficient electrical energy include machine-executable programming instructions that configure the electronic device to perform the following operations: disconnecting the negative terminal of the solar panel from the ground terminal; and detecting a negative voltage at the negative terminal of the solar panel by a voltage sensor.

33. The electronic device according to claim 32, wherein: The voltage sensor includes an operational amplifier having an inverting input, a non-inverting input, a positive power supply terminal, a negative power supply terminal, and an output terminal; the negative power supply terminal is connected to the negative terminal of the solar panel; the output terminal of the operational amplifier is connected to the inverting input terminal; the voltage sensor signal of the voltage sensor is the output of the operational amplifier; the non-inverting input terminal of the operational amplifier is connected to ground; and machine-executable programming instructions for configuring the electronic device to enable the voltage sensor include machine-executable programming instructions for configuring the electronic device to have the signal connected to the positive power supply terminal of the operational amplifier set to valid by the controller.

34. The electronic device according to claim 33, wherein: The voltage sensor signal of the voltage sensor includes a positive analog signal; and the machine-executable programming instructions that configure the electronic device to read the voltage sensor signal of the voltage sensor include machine-executable instructions that configure the electronic device to convert the positive analog signal into a digital value.

35. The electronic device according to any one of claims 31 to 34, wherein: The negative terminal of the solar panel is connected to a ground terminal via an N-channel field-effect transistor (NFET) switch having a source, a gate, and a drain; the NFET switch is connected to the ground terminal at its source and to the negative terminal of the solar panel at its drain; and machine-executable programming instructions configuring the electronic device to determine that the solar panel is generating sufficient energy include machine-executable programming instructions configuring the electronic device to detect a negative voltage at the drain of the NFET switch.

36. The electronic device according to any one of claims 31 to 35, wherein, Machine-executable programming instructions configuring the electronic device to disconnect the rechargeable battery from the unregulated voltage bus include machine-executable programming instructions configuring the electronic device to perform the following operations: disconnecting the top battery switch between the positive terminal of the rechargeable battery and the unregulated voltage bus; and disconnecting the bottom battery switch between the negative terminal of the rechargeable battery and the ground terminal.

37. The electronic device according to any one of claims 31 to 36, wherein, The machine-executable programming instructions also configure the electronic device to: in response to determining that the rechargeable battery is connected to the unregulated voltage bus; in response to determining that the rechargeable battery is defective based on the voltage of the unregulated voltage bus; and in response to determining that the solar panel provides sufficient power to power the network interface of the electronic device, power the network interface and send a notification to a remote server indicating that the rechargeable battery is defective.

38. The electronic device according to any one of claims 31 to 37, wherein, The machine-executable programming instructions also configure the electronic device to: in response to determining that the rechargeable battery is disconnected from the unregulated voltage bus; in response to determining a potential undervoltage condition based on the voltage of the unregulated voltage bus; connect the rechargeable battery to the unregulated voltage bus.

39. The electronic device according to claim 38, wherein, The machine-executable programming instructions also configure the electronic device to: in response to determining that the rechargeable battery is disconnected from the unregulated voltage bus; in response to determining a potential undervoltage condition based on the voltage of the unregulated voltage bus; and in response to determining that the solar panel is not generating sufficient electrical energy, disconnect the solar panel from the ground terminal at its negative terminal.

40. The electronic device according to claim 39, wherein: The negative terminal of the solar panel is connected to the ground terminal via an N-channel field-effect transistor (NFET) switch having a source, a gate, and a drain; the NFET switch is connected to the ground terminal at its source and to the negative terminal of the solar panel at its drain; and machine-executable programming instructions configuring the electronic device to determine that the solar panel is not generating sufficient energy include machine-executable programming instructions configuring the electronic device to detect a positive voltage at the drain of the NFET switch.

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