Wireless power supply intelligent water meter direct reading system

Abstract

The invention discloses a wireless power supply intelligent water meter direct reading system, and relates to the field of intelligent water meters, the wireless power supply intelligent water meter direct reading system comprises an intelligent water meter terminal and an external reading device, the terminal comprises a mechanical metering and photoelectric encoder, a wireless energy collection and power supply management module, a microcontroller and a modulation and demodulation module; external equipment wirelessly supplies power to the water meter by transmitting a high-frequency electromagnetic field and realizes two-way communication, the system adopts a passive design, the water meter is powered by external induction only at the moment of reading, and then is completely powered off, so that lifelong maintenance-free and infinite service life of the terminal are realized; the absolute digital code of the mechanical position is directly obtained through the cyclic Gray code disc on the end face of the photoelectric scanning character wheel, so that the accumulative error and critical point hop count risk are fundamentally eliminated, and absolute accuracy and reliability of data reading are ensured. The intelligent water meter is converted into a metering infrastructure which is zero in power consumption, high in reliability and almost zero in operation and maintenance cost, and an ideal solution is provided for water affair management.

Description

Technical Field

[0001] This invention relates to the field of smart water meters, specifically to a wirelessly powered smart water meter direct reading system. Background Technology

[0002] With the deepening of smart city and smart water management construction, traditional mechanical water meters, unable to achieve remote automatic data collection, are no longer able to meet the needs of efficient and accurate modern water resource management. As the core of metering terminals, the technological development of smart water meters mainly revolves around automatic data reading and remote transmission. Currently, mainstream smart water meters on the market still have several inherent defects in power supply, data collection, and communication interfaces, which restrict their large-scale, high-reliability application.

[0003] The current technical solutions mainly suffer from the following problems:

[0004] Lifespan and Maintenance Bottlenecks of Built-in Battery Power Supply Solutions: Most smart water meters use built-in lithium batteries (such as lithium-thionyl phosphate batteries) to power their circuits, sensors, and communication modules. However, battery capacity is limited, especially under frequent communication or extreme temperature environments, with a lifespan typically only 3-8 years. Battery depletion means the entire smart water meter fails, requiring manual replacement, leading to high maintenance costs and operational disruptions. Furthermore, batteries pose safety hazards such as leakage and high-temperature explosions, and their capacity decreases sharply in low-temperature environments, affecting the normal use of water meters in northern winters.

[0005] The sealing challenges posed by external power supply and communication interfaces: Some water meters that use external power supplies (such as M-BUS bus power supply) or have wired communication interfaces (such as RS-485) require electrical interfaces to be installed on the meter casing. These interfaces become weak points for the intrusion of moisture, dust, and corrosive gases. Even with sealing rings, they are still prone to aging and failure after long-term use, leading to moisture and corrosion of the circuit board. This makes it difficult for them to work stably in humid and water-immersed environments such as underground wells and in the field, limiting their application scenarios.

[0006] Energy supply challenges for wireless meter reading technology: Smart water meters using active wireless communication (such as LoRa and NB-IoT) have high peak current during radio frequency module transmission, resulting in significant battery drain. Although there have been attempts to use energy harvesting (such as hydropower), their output power is unstable and their structure is complex, making it difficult to guarantee reliable power supply under low flow rates or no water flow conditions.

[0007] In summary, existing smart water meter technology struggles to comprehensively address the four core requirements of power supply lifespan, environmental sealing, data source reliability, and low-power operation. Summary of the Invention

[0008] The purpose of this invention is to provide a wirelessly powered smart water meter direct reading system that can fundamentally eliminate battery dependence, achieve full-sealed protection, directly obtain absolute metering values, and quickly establish reliable communication when needed, thereby solving the problems mentioned in the background art.

[0009] To achieve the above objectives, the present invention provides the following technical solution: comprising a smart water meter terminal and an external reading device, characterized in that: the smart water meter terminal comprises:

[0010] A mechanical metering unit, comprising at least one set of digits for displaying water consumption figures;

[0011] An encoder, directly coupled to the character wheel, is used to acquire the digital code of the current mechanical position state of each character wheel in parallel at the moment of power supply.

[0012] A wireless power transmission module is used to collect electrical energy from an external alternating electromagnetic field and provide instantaneous operating power to the smart water meter terminal;

[0013] A microcontroller is connected to the wireless power transmission module and the encoder. It is powered by the wireless power transmission module and controls the encoder to work and decode its output digital code after power-on reset to obtain the current water volume data.

[0014] The external reading device includes an energy emission and communication module for generating the external alternating electromagnetic field, sending downlink commands to the smart water meter terminal and receiving uplink data from the smart water meter terminal. The microcontroller responds to the downlink commands by returning a response frame containing the water consumption data to the external reading device through load modulation.

[0015] Preferably, the encoder includes a Gray code disk disposed on a mechanical character wheel and a photoelectric sensor array corresponding to the code track. The Gray code disk has a cyclic Gray code pattern consisting of light-transmitting and light-blocking areas corresponding to the position of the character wheel. The photoelectric sensor array includes an infrared emitting tube and an infrared receiving tube, which are used to generate light pulses and capture the state of the Gray code disk at the moment of power supply.

[0016] Preferably, the Gray code pattern on the Gray code disk is designed such that the codes of any two adjacent numbers differ by only one bit; the photoelectric sensor array is sealed and encapsulated in a light-proof dark chamber.

[0017] Preferably, the communication between the smart water meter terminal and the external reading device includes:

[0018] Downlink communication: The external reading device sends commands via amplitude shift keying modulated carrier wave, and the smart water meter terminal demodulates and decodes the commands via envelope detection circuit and comparator;

[0019] Uplink communication: The smart water meter terminal controls the on / off state of the switching tubes connected in parallel across the induction coil to perform load modulation on the electromagnetic field generated by the external reading device, and returns data in frequency shift keying or phase shift keying mode.

[0020] Preferably, the wireless power transfer module includes:

[0021] The energy receiving antenna uses a planar helical coil or a multi-layer PCB coil to sense external alternating electromagnetic fields.

[0022] The parallel resonant circuit, consisting of a resonant capacitor connected in parallel with the energy receiving antenna, is used to increase the induced voltage.

[0023] A rectifier circuit, consisting of Schottky diodes with low forward voltage drop, is a full-bridge rectifier circuit used to convert alternating current induced by a parallel resonant circuit into direct current.

[0024] Preferably, the wireless power transmission module further includes a power management unit, which includes:

[0025] An energy storage element is connected to the output terminal of the rectifier circuit and is used to store electrical energy. The energy storage element is a double-layer supercapacitor.

[0026] A linear regulator, connected to the energy storage element, is used to provide a stable voltage to the microcontroller;

[0027] A voltage monitor, connected to the output of the linear regulator, is configured to: when the output voltage of the linear regulator does not reach a preset threshold, output a reset signal to the microcontroller to keep it in a reset state; and when the voltage reaches and stabilizes at the preset threshold, release the reset signal to allow the microcontroller to start working.

[0028] Preferably, the microcontroller reads the digital code from the encoder, specifically including the following steps:

[0029] A short-time pulse current is supplied to the photoelectric emitter in the encoder to make it emit detection light;

[0030] After the pulse ends, the states of all photodetectors are read in parallel to obtain the parallel Gray code representing the position of the character wheel;

[0031] The parallel Gray code is converted into decimal numbers corresponding to each word wheel using an internally stored decoding table, and then synthesized into the final water consumption data.

[0032] Preferably, the energy transmission and communication module includes a high-frequency signal generator for generating a carrier signal of a predetermined frequency. The high-frequency signal generator is connected to a power amplifier for amplifying the carrier signal. The output of the power amplifier is connected to an impedance matching network, and the impedance matching network is connected to a transmitting coil for generating the external alternating electromagnetic field based on the amplified carrier signal.

[0033] Preferably, the external reading device further includes a main controller, which is configured to perform the following steps:

[0034] During the initial carrier transmission, the coupling field strength with the smart water meter terminal is sensed by detecting the current or voltage of the transmitting coil, and the output of the power amplifier is dynamically adjusted to make the field strength reach a preset working threshold.

[0035] Uplink data reception steps: After sending downlink commands, monitor the changes in electrical parameters of the transmitting coil circuit to demodulate the uplink data sent back by the smart water meter terminal through load modulation.

[0036] Preferably, the external meter reading device also includes a human-machine interface for displaying meter reading status, water meter reading and device information; and a data storage unit for storing meter reading records.

[0037] In summary, the beneficial effects of this invention are:

[0038] This invention utilizes two core technologies—wireless power supply and absolute direct reading—to achieve a water meter terminal that requires no built-in battery. It only receives power momentarily during external meter reading, completes the reading, and then completely shuts off, thus achieving lifetime maintenance-free operation and unlimited lifespan, significantly reducing long-term maintenance costs. Simultaneously, it employs photoelectric scanning and cyclic Gray code to directly interpret the absolute position of the mechanical dial, fundamentally eliminating cumulative errors and critical jump counts, ensuring absolutely accurate and reliable data for every reading. This fundamentally avoids metering disputes, ultimately making the smart water meter a reliable metering infrastructure that offers accurate data, flexible deployment, security, and near-zero cost. Attached Figure Description

[0039] To more clearly illustrate the technical solutions in the embodiments of the invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0040] Figure 1 This is a schematic diagram of the overall process framework of a wirelessly powered smart water meter direct reading system according to the present invention;

[0041] Figure 2 This is a schematic diagram of the microcontroller operation process framework in a wirelessly powered smart water meter direct reading system according to the present invention.

[0042] Figure 3 This is a schematic diagram of the operation process framework of the external reading device in a wirelessly powered smart water meter direct reading system of the present invention;

[0043] Figure 4 This is a schematic diagram of the encoder in a wirelessly powered smart water meter direct reading system according to the present invention.

[0044] Figure 5 This is a schematic diagram of the energy receiving antenna structure of a smart water meter in a wirelessly powered smart water meter direct reading system according to the present invention;

[0045] Figure 6 This is a schematic diagram of the transmitting coil structure of the external reading device in a wirelessly powered smart water meter direct reading system of the present invention;

[0046] Figure 7 This is a schematic diagram of the internal circuit module structure of the external reading device in a wirelessly powered smart water meter direct reading system of the present invention. Detailed Implementation

[0047] The present invention will now be described in further detail with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention. These drawings are simplified schematic diagrams, which are only used to illustrate the basic structure of the present invention in a schematic manner, and therefore only show the components related to the present invention.

[0048] To facilitate understanding of the present invention, a more complete description of the invention will be given below with reference to the accompanying drawings, which illustrate several embodiments of the invention. However, the invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that the disclosure of the invention will be more thorough and complete.

[0049] All features disclosed in this specification, or all steps in all disclosed methods or processes, may be combined in any way, except for mutually exclusive features and / or steps.

[0050] Any feature disclosed in this specification (including any appended claims, abstract, and drawings) may be replaced by other equivalent or similar features, unless specifically stated otherwise. That is, unless specifically stated otherwise, each feature is merely one example of a series of equivalent or similar features.

[0051] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, a direct connection, or an indirect connection through an intermediate medium; they can refer to the internal communication of at least two elements or the interaction relationship of at least two elements, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0052] Please see Figures 1-7 The present invention provides an embodiment of a wirelessly powered smart water meter direct reading system, which consists of two parts:

[0053] Smart water meter terminal: Internally includes a mechanical metering unit, encoder (photoelectric / resistive / magnetic sensing), energy harvesting and power management module, microcontroller (MCU) and modulation / demodulation module, and induction coil.

[0054] External meter reading device: responsible for generating a high-frequency electromagnetic field to power the water meter, while sending commands and receiving data returned by the water meter.

[0055] Specifically, refer to Figure 1 and Figure 2 The smart water meter terminal includes the following modules:

[0056] First Module: Mechanical Measurement and Encoder

[0057] The core objective is to accurately convert the absolute physical position of the mechanical digit wheel into a unique digital code in real time, and the entire process is completed only when the external power supply is applied, resulting in extremely low power consumption.

[0058] Base meter selection: First, choose between pointer type or dial type base meter. Considering intuitiveness and ease of installation, dial type water meters are currently the mainstream.

[0059] Encoding carrier: A special black plastic code disk is inlaid or injection molded on the coaxial end face or side of each character wheel that needs to be read. The code disk is formed with opaque and translucent areas by precision printing or laser engraving. The opaque area can be black and the translucent area can be white.

[0060] The system employs cyclic Gray code. Gray code means that the encoding of any two adjacent numbers differs by only one bit. This means that when the digit wheel rotates between adjacent numbers, such as from "4" to "5", only one photocell will change state. This fundamentally avoids "garbled codes" or "jumping numbers" caused by mechanical jitter or slight differences in photoelectric signals at critical positions of the digit wheel (such as 4.99→5.01), ensuring the absolute reliability of the reading.

[0061] For example, a number wheel displaying 0-9 requires 4 bits of binary data (2^32). 4 =16 > 10) to represent its 10 positions. Therefore, the code wheel has 4 concentric rings of code tracks, each ring corresponding to one bit of binary code.

[0062] refer to Figure 4 One structural diagram is shown below:

[0063] One of the digits on the wheel-type water meter points to 5;

[0064] Example of a code disk pattern (Gray code, position 5):

[0065] Innermost ring (representing the highest position): Opaque

[0066] Second track: Translucent

[0067] Third track: Opaque

[0068] The outermost ring (representing the lowest digit): translucent

[0069] correspond Figure 4 The physical state of the sector containing the digit "5":

[0070] Bit 3 (innermost ring): Opaque (black) - Logic "0"

[0071] Bit 2 (Second Ring): Transparent (white) - Logic "1"

[0072] Bit 1 (Third Ring): Opaque (Black) - Logic "1"

[0073] Bit 0 (outermost ring): Transparent (white) - Logic "1"

[0074] The reading is: 0111 (Gray code) → converted to decimal 5.

[0075] This set of states [opaque, translucent, opaque, translucent] corresponds to the unique code of the number "5".

[0076] Photoelectric sensing unit: Fixed at a position on the other side of the code disk, not rotating with the character wheels, it houses a photoelectric sensor array aligned one-to-one with the code tracks of the code disk. Typically, each character wheel corresponds to an independent sensor board, and the sensor components include:

[0077] Infrared emitter: Located on one side of the code disk, usually on the same circuit board as the receiver, aligned via a light guide post. At the moment of meter reading, the MCU controls a pulsed power supply to emit invisible infrared light. Pulse operation significantly reduces power consumption.

[0078] Infrared receiver tubes: Located on the opposite side of the code disk or on the same side as the transmitter tube, they operate on a reflective principle, but transmissive models are more reliable. Each receiver tube is precisely aligned with one ring of code tracks. When the light-transmitting area of ​​the code disk is aligned, the receiver tube conducts and outputs a low level; when the opaque area is aligned, the receiver tube is cut off and outputs a high level.

[0079] The entire photoelectric sensor array is encapsulated in a sealed, light-proof dark chamber to prevent interference from external visible light. Only through a precision structure do the transmitting and receiving light paths pass through the code disk. This also provides physical isolation from any condensation that may exist inside the water meter.

[0080] The entire signal processing procedure is as follows:

[0081] Power supply and startup: When an external reading device approaches, the water meter receives power. The MCU starts up, first providing a short pulse current to the photoelectric emitter array.

[0082] Optical signal capture: Infrared light passes through or reflects off a rotating code disk, and each receiving tube generates an "on / off" level signal according to the "transparent / opaque" state of its corresponding code track.

[0083] Data latching and reading: The level states of all receiving tubes are sent in parallel to a set of I / O ports of the MCU, or latched instantaneously by a latch chip. At this time, the MCU reads a set of multi-bit parallel binary numbers (for example, a water meter with 4 digits has 4 sets of 4-bit = 16-bit data).

[0084] Data Conversion: The MCU's internal firmware stores a conversion table between Gray code and natural binary code or directly between Gray code and decimal numbers. It instantly decodes this Gray code into the decimal number (0-9) corresponding to each character wheel.

[0085] Data synthesis: The digits of all the dials are combined according to their place values ​​to obtain the final, absolute water meter reading, such as "01234.5 m³". This reading is independent of the previous reading and historical cumulative values, and depends only on the current physical position of the dial.

[0086] Power outage: The entire process is completed within 10 milliseconds, after which the system is powered off. The encoder section no longer consumes any energy.

[0087] Second module: Wireless power transfer;

[0088] Its core task is to capture weak alternating electromagnetic field energy from the outside with maximum efficiency, convert it into stable and clean direct current, and provide reliable operating timing for digital circuits such as microcontrollers (MCUs) and encoders. This mainly includes:

[0089] a) Energy receiving antenna (coil L1), reference Figure 5 ;

[0090] Achieve high coupling coefficient (k) and quality factor (Q) to maximize induced electromotive force and energy transfer efficiency.

[0091] Planar spiral coils or multi-layer PCB coils are used, printed or pasted on the inside of the water meter casing, in the non-metallic area or under a special non-metallic window, to save space and facilitate mass production.

[0092] Inductance value (L1): Calculated based on the selected operating frequency (f) and resonant capacitance (C1).

[0093] For example, for 125kHz, L1 is typically in the range of several hundred microhenries to several millihenries; for 13.56MHz, it is several microhenries.

[0094] Q-value improvement: Use multi-strand Litz wire (low frequency) or wide copper foil PCB traces (high frequency) to reduce skin effect resistance at high frequencies.

[0095] b) Parallel resonant and rectifier circuits;

[0096] Resonant matching: The parallel resonance of capacitor C1 and coil L1. Parallel resonance presents high impedance at the resonant point, thus a higher AC voltage can be induced across the coil under the same magnetic field strength. Capacitor C1 must be an NPO / COG ceramic capacitor with good high-frequency characteristics and high temperature stability.

[0097] High-efficiency rectifier bridge: Since the induced voltage amplitude may be low, typically a few volts to tens of volts, Schottky diodes with extremely low forward voltage drop (Vf), such as the BAT series, must be selected to form a full-bridge rectifier circuit. The four diodes must be well matched to reduce losses and ripple.

[0098] c) Power Management Unit (PMU):

[0099] Energy storage components: Double-layer supercapacitors are the first choice because their capacitance density is much higher than that of ordinary capacitors, typically 0.1F to 1F, which can provide hundreds of millijoules of energy required for MCU operation. Tantalum capacitors are the second choice because they have smaller capacitance but extremely low leakage current.

[0100] The rated voltage must be higher than the peak voltage after rectification, with sufficient margin (such as choosing 5.5V or higher).

[0101] The equivalent series resistance must be extremely low. A high ESR will cause a severe voltage drop during a high-current discharge, leading to a system reset.

[0102] Leakage current must be extremely low. This is key to achieving "zero-power standby," ensuring that the stored energy is not depleted between two meter readings.

[0103] Linear Regulator (LDO): Converts the fluctuating voltage on the energy storage capacitor, such as 2V-5V, into a stable 3.3V required by the MCU. LDOs effectively suppress high-frequency noise from the rectifier, provide power to sensitive digital circuits, and consume very little current under no-load or light-load conditions, without consuming additional energy.

[0104] Power-on reset and voltage monitoring: This is typically implemented using a voltage monitor chip or a custom circuit consisting of a comparator and an RC circuit.

[0105] Work logic:

[0106] Power-on phase: The external field is turned on, and the energy storage element begins to charge. When the LDO output voltage rises slowly but does not reach the reliable operating voltage of the MCU, such as 2.7V, the / RESET pin of the voltage monitor remains low, forcing the MCU to be in a reset state.

[0107] Release Phase: Once the LDO output voltage is detected to be stable and exceeds the set threshold, and remains so for a period of time, the voltage monitor will pull the / RESET pin high to release the MCU. This ensures that the MCU only begins executing instructions after the power supply is fully stable, preventing program crashes.

[0108] Power failure protection: When the external field is removed and the voltage of the energy storage element drops below the threshold, the voltage monitor will quickly pull / RESET low, so that the MCU can complete the necessary state saving or enter a safe state before the voltage completely fails.

[0109] The timing sequence of wireless power transfer is as follows:

[0110] Energy Capture Period (T1): The external meter reader approaches and transmits a continuous carrier wave. The water meter coil induces an AC voltage, which, after resonant amplification and rectification, charges the energy storage element. The voltage begins to rise from 0V. During this stage, although the LDO has an output, the MCU remains dormant because the voltage monitor has not been released.

[0111] System startup (T2): The energy storage element voltage brings the LDO output to a stable value (3.3V). After confirming that the power supply is "clean and stable," the voltage monitor releases the reset signal. The MCU begins executing the boot program, initializing I / O, timers, etc.

[0112] Active Operating Period (T3): The MCU controls the encoder to power on, performing optical pulse readings, data processing, modulation, and communication. During this period, the energy storage element acts as the sole power source, bearing the instantaneous large pulse load, especially when the infrared emitter is lit. Its low ESR characteristic is crucial to prevent sudden voltage drops from causing a system restart.

[0113] Communication End and Power-Off Period (T4): The external reading device stops transmitting the carrier wave. The remaining energy in the energy storage element is slowly consumed by the LDO and the static power consumption of the circuit itself until the voltage monitor pulls low again to reset, and the system is completely powered off. The leakage current determines the duration of this process.

[0114] Third Module: Wireless Communication

[0115] 1. Downlink communication is from the external meter reader to the water meter: ASK demodulation and command decoding.

[0116] a) External reading device sends ASK modulation:

[0117] Modulation method: Amplitude shift keying with a modulation depth of 10%-30% is used.

[0118] For example, taking a 125kHz carrier as an example, when transmitting "1", the carrier amplitude is 100%; when transmitting "0", the carrier amplitude drops to 70%-90%. This depth is a balance between energy transmission efficiency and signal demodulation sensitivity.

[0119] The frame structure uses Manchester encoding or differential encoding and includes a preamble, frame start, water meter address, command word, CRC check, etc. The preamble is used to wake up the water meter MCU and help it synchronize its clock.

[0120] b) Water meter terminal demodulation circuit design:

[0121] Since the parallel resonant circuit of the water meter coil (L1) carries ASK modulation information at the same time as it acquires energy, the demodulation circuit must extract the digital baseband signal from the high voltage and high frequency signal with extremely low power consumption.

[0122] The circuit includes:

[0123] Envelope Detector: A signal is drawn from the L1 / C1 resonant circuit through a small-capacity coupling capacitor (e.g., 10pF). A Schottky diode with ultra-low junction capacitance and low forward voltage drop (e.g., HSMS-2850) is used for peak detection. An RC low-pass filter is connected after the diode, with a time constant much larger than the carrier period but smaller than the data bit period, to filter out the high-frequency components of the carrier signal and obtain the envelope of the baseband signal.

[0124] Bias and Amplification: The detected signal level is low and has a DC bias. It can be fed into a low-power comparator (such as LTC1540) or the analog comparator built into the MCU through a high-resistance voltage divider network. It is compared with a reference voltage, thereby shaping the analog envelope signal into a clean digital signal (0 / 1) and directly fed into the MCU's I / O port.

[0125] Coordination with power management: This section of the circuit is powered by the 3.3V output from the LDO. The MCU will only enable this section of the circuit after the voltage monitor releases the MCU reset, avoiding unnecessary power consumption.

[0126] After the MCU is woken up, it immediately configures a timer to capture the edge of the digital signal output from the comparator, performs baud rate self-calibration using the preamble and start-of-frame bit, and then receives subsequent data bits in interrupt mode. After successful decoding and CRC check, the MCU enters the response process.

[0127] 2. Uplink communication is from the water meter to the external data reading device: load modulation and data feedback.

[0128] Water meters can communicate by consciously changing their "absorption" state of electromagnetic fields, thereby affecting the parameters that external reading devices can detect.

[0129] a) Load modulation principle and circuit implementation:

[0130] Core component: Load modulation switch (MOSFET M1), a low on-resistance (Rds_on) NMOS transistor, whose drain and source are connected in parallel across the energy receiving coil L1.

[0131] Modulation process:

[0132] When M1 is closed, the water meter behaves as a normal parallel resonant load.

[0133] When M1 is turned on, it is equivalent to connecting a small resistor (Rds_on) in parallel across L1, which significantly reduces the Q value of the resonant circuit, causing the power absorbed by the coil to increase instantaneously.

[0134] According to Lenz's law, the driving current of the external meter reader's transmitting coil (L2) will increase to maintain a stable magnetic field. Therefore, changes in the water meter's load are "mapped" to changes in the current / voltage of the external meter reader's coil.

[0135] b) Modulation method selection and implementation:

[0136] FSK (Frequency Shift Keying) scheme (recommended for lower frequencies such as 125kHz):

[0137] The MCU controls M1 to switch on and off at two different frequencies, such as f1 = carrier frequency / 16 and f2 = carrier frequency / 32. Changing the switching frequency results in different rates of load change.

[0138] External reading device demodulation: The external reading device detects its coil current and, through a set of bandpass filters or digital signal processing (DSP) algorithms, identifies the energy corresponding to f1 and f2, demodulating "0" and "1". FSK has strong anti-amplitude interference capability.

[0139] PSK (Phase Shift Keying) scheme (commonly found at 13.56MHz):

[0140] The data "0" and "1" are reflected in the relative relationship between load switching and carrier phase. For example, load switching at the zero-crossing point of the carrier represents "0", and switching at the peak point of the carrier represents "1".

[0141] External reading device demodulation: requires more complex phase detection circuits, but has higher data rate and spectral efficiency.

[0142] The communication workflow is as follows:

[0143] Energy and Synchronization Phase: The external meter reader transmits an unmodulated continuous carrier wave (lasting approximately 50-100ms) to charge the water meter's energy storage capacitor (C_store) until the voltage monitor releases and the MCU resets. This phase also establishes a stable carrier reference for subsequent ASK demodulation.

[0144] Downlink command phase: The external meter reader switches to transmitting ASK-modulated command frames (e.g., "Read water meter at address 0x01"). The water meter MCU enables the demodulation circuit, receives and decodes the command. If the address matches, it prepares to respond.

[0145] Data acquisition stage: The MCU first controls the infrared transmitter to emit short pulses, reads the parallel Gray code of the photoelectric encoder, and converts it into water volume data. During this stage, load modulation is paused.

[0146] Uplink response phase: The MCU controls MOSFET M1 to perform load modulation on the response frame containing water volume data and CRC checksum according to FSK / PSK mode, and sends it back to the external reading device.

[0147] Terminal phase: After the external data reader successfully receives and verifies the data, it stops transmitting the carrier wave. The water meter's energy storage capacitor is depleted, and the system is completely powered off and reset.

[0148] The detailed design for each state of the microcontroller (MCU) is as follows:

[0149] State 1: Power-on and Initialization

[0150] Clock Configuration: Immediately switch the system clock to the internal high-speed RC oscillator (e.g., 16MHz) without waiting for the external crystal to start, achieving the fastest boot time. Turn off all unnecessary peripheral clocks.

[0151] GPIO initialization:

[0152] Set the encoder input pin to pull-up input mode; the internal weak pull-up can determine the pin state when the encoder is not powered.

[0153] Set the infrared emitter control pin to push-pull output and initialize it to low level;

[0154] Set the load modulation MOSFET control pin to push-pull output and initialize it to low level;

[0155] Set the analog comparator output pin (if used) as an input and configure its multiplexing function.

[0156] Peripheral initialization:

[0157] Configure a timer (TimerA) to generate precise timing parameters, such as infrared pulse width and modulation frequency.

[0158] Configure the analog comparator, set the reference voltage, and use the internal DAC or resistor divider for ASK demodulation, and enable the CRC hardware unit.

[0159] State 2: Command Listening and Decoding

[0160] Enable demodulation: Enable the analog comparator, or configure an external interrupt to trigger on the edge of the demodulated digital signal.

[0161] Synchronization and Decoding:

[0162] Waiting for the detection of a continuous preamble, such as the pattern "101010...", the system uses a timer to measure its period and dynamically calculates the precise baud rate for this communication to compensate for minor deviations in the transmission frequency of the external transceiver.

[0163] Enter byte receiving state to receive subsequent address, command, and CRC data via interrupt.

[0164] Verification and Judgment:

[0165] After receiving the data, use hardware CRC to verify it.

[0166] If verification fails or the address does not match: immediately jump to the "safe termination" state. In this state, the MCU places all I / Os in the lowest power state and loops in place or enters a low-power mode, quietly waiting for the external field to be evacuated, capacitors to discharge, and the system to be reset. No meaningless responses or retries are performed to conserve energy.

[0167] If the verification is successful and the address matches: prepare to enter the data collection state.

[0168] Status 3: Data Acquisition

[0169] Power supply and reading:

[0170] Temporarily change the encoder input pin to a high-impedance input to avoid conflict.

[0171] The infrared emitter's control pin outputs a short pulse (e.g., a 1ms high level). Simultaneously, a timer is started.

[0172] After the pulse ends and the photodetector output stabilizes (marked by a timer interrupt), the state of the encoder input pin is immediately read in parallel into a 16-bit variable in the MCU. The entire process is completed within milliseconds.

[0173] Data transformation:

[0174] The original Gray code read is quickly converted into a decimal number (0-9) for each character wheel using a lookup table or calculation method.

[0175] The values ​​of each digit are combined and multiplied by a constant (e.g., 0.001 m³ / digit) to obtain the final water consumption value.

[0176] This data is packaged with its own address and other information, a new CRC is calculated, and a response data frame is formed.

[0177] State 4: Data Response (Load Modulation)

[0178] Timing: Ensure that the infrared emitter is off and that the capacitor voltage has recovered from the load during the acquisition phase (this can be achieved through a short delay or by monitoring the ADC—if available).

[0179] Modulation transmission:

[0180] The modulation subroutine is invoked based on each bit of the response data frame.

[0181] For FSK: For bit '0', the control MOSFET is switched on and off at frequency f0; for bit '1', it is switched on and off at frequency f1. The duty cycle for switching on and off is typically 50%. A timer is used to generate a precise square wave.

[0182] Key optimization: Modulation should begin at a specific phase of the carrier (such as a zero-crossing) to enhance the demodulation effect of the external reading device. This may require obtaining carrier phase information by detecting the coil voltage, dividing it, and then connecting it to an ADC or comparator.

[0183] Transmission complete: After the last bit has been transmitted, immediately set the MOSFET control pin low to turn off modulation.

[0184] State 5: Communication Completed and Power Off

[0185] Silent wait: After all tasks are completed, the MCU executes a __low_power_mode_0() or similar instruction to enter the deepest low-power mode, or directly stops all activities in an infinite empty loop.

[0186] Natural Reset: The external reader stops transmitting, and the voltage of the energy storage capacitor (C_store) continues to drop due to LDO and circuit leakage. When the voltage falls below the MCU's minimum operating voltage, the MCU stops operating. Subsequently, the voltage monitor (POR) outputs a reset signal. Finally, the entire system returns to a completely power-depleted physical reset state, ready for the next interaction.

[0187] For external reading devices, refer to Figure 3 and Figure 7 It includes the following modules:

[0188] Energy transmission and communication module: Enables coupled transmission and reception of energy and data, including the following components:

[0189] 1. High-frequency signal generator: generates a high-frequency sinusoidal carrier wave with a highly stable frequency.

[0190] The commonly used frequency is 125kHz, which has strong penetration and relatively long communication distance, but the data rate is low or 13.56MHz, the ISO / IEC 15693 / 14443 standard frequency band. It has high device integration and high data rate.

[0191] Dedicated RF transmitter chips can be used, such as the NXP CLRC663 series for 13.56MHz, or a microcontroller with built-in PWM that is filtered and amplified for 125kHz, or an oscillator composed of a crystal oscillator and gate circuits.

[0192] 2. Power Amplifier (PA) and Impedance Matching Network:

[0193] Power amplifier: Amplifies the carrier wave generated by the signal generator to sufficient power, typically 1W-5W, to drive the transmitting coil to generate a strong magnetic field. A high-efficiency Class D or Class E amplifier should be selected.

[0194] Impedance matching network: An LC network composed of inductors and capacitors, typically π-type or L-type. Its core functions are twofold:

[0195] Matching the output impedance of the power amplifier (typically 50Ω) to the complex impedance of the transmitting coil (L2) allows energy to be transferred to the magnetic field with maximum efficiency, rather than being reflected or heated.

[0196] Harmonic components in the power amplifier output signal are filtered out to ensure a clean transmission spectrum that complies with radio management regulations.

[0197] 3. Transmitting coil (L2):

[0198] refer to Figure 6 It is typically a planar helical coil, built into the head of the device. Its size and inductance value need to be precisely designed with the matching network and operating frequency.

[0199] To accommodate different installation locations of water meters, a ferrite core backplate can be added behind the coil. This enhances the focusing of the magnetic field forward (towards the water meter) and improves coupling efficiency. It also shields the magnetic field from leaking to the rear of the device, reducing interference with the device's own circuitry and lowering power consumption.

[0200] The main control and interaction module includes:

[0201] Main controller: Responsible for controlling the timing of the entire device, executing communication protocols, processing data, and managing the human-machine interface. It needs to integrate a high-speed ADC to sample the analog signals of the demodulation circuit, or directly connect to a dedicated RF demodulation chip through a digital interface (such as SPI).

[0202] Human-computer interaction interface: used to display device status (such as field strength, power), water meter address, water volume data, operation prompts, etc.

[0203] Data storage and communication: Used to store tens of thousands of meter reading records, including water meter address, reading, and reading time.

[0204] The overall workflow is as follows:

[0205] The user places the device close to the water meter and presses the "meter reading" button.

[0206] The main controller controls the RF front end to transmit the carrier at low power and starts the field strength detection feedback loop, which can be achieved by detecting the coil current.

[0207] The main controller dynamically adjusts the power amplifier output power until the field strength reaches the preset threshold, indicating that good coupling has been achieved and the system has entered a stable transmission mode.

[0208] Downlink communication (send command):

[0209] On a stable carrier, ASK modulation is used to transmit a "wake-up query" command frame. The command includes a preamble, synchronization header, target water meter address, command code, and CRC.

[0210] After transmission is completed, the power amplifier switches to continuous constant amplitude carrier transmission mode to power the water meter and prepare to receive uplink signals.

[0211] Uplink communication (receiving data):

[0212] The main controller initiates the signal output by the ADC sampling and demodulation circuit, or enables the interrupt of the dedicated demodulation chip.

[0213] Within a preset time window, attempt to capture and demodulate the load modulation signal of the water meter response.

[0214] Perform CRC check on the received data. If the check is successful, store and display the data and issue a success tone; if it fails, automatically retry 1-2 times.

[0215] After a single meter reading is completed, the power amplifier is turned off and the device enters a low-power standby state.

[0216] You can wake it up by pressing a button, browse historical data, or perform batch export.

[0217] In summary, this invention, through its two core technologies of passive design and absolute direct reading, completely eliminates the need for a built-in battery. The water meter terminal only obtains instantaneous energy through wireless sensing when an external reading device is nearby, and completely cuts off power after completing the reading. This achieves lifetime maintenance-free operation and unlimited service life, greatly reducing long-term operating costs.

[0218] Meanwhile, it uses photoelectric scanning and cyclic Gray code to directly interpret the absolute position of the mechanical character wheel, which eliminates cumulative errors and critical jumps in principle, ensuring the absolute accuracy and reliability of each data reading and fundamentally avoiding measurement disputes.

[0219] Ultimately, smart water meters are transformed from "electronic devices" requiring periodic maintenance into a reliable metering infrastructure that provides accurate data, flexible deployment, security, and near-zero cost, offering an ideal solution for water management.

[0220] The above description is merely a specific embodiment of the invention, but the scope of protection of the invention is not limited thereto. Any variations or substitutions conceived without inventive effort should be included within the scope of protection of the invention. Therefore, the scope of protection of the invention should be determined by the scope defined in the claims.

Claims

1. A wirelessly powered smart water meter direct reading system, comprising a smart water meter terminal and an external reading device, characterized in that: The smart water meter terminal includes: A mechanical metering unit, comprising at least one set of digits for displaying water consumption figures; An encoder, directly coupled to the character wheel, is used to acquire the digital code of the current mechanical position state of each character wheel in parallel at the moment of power supply. A wireless power transmission module is used to collect electrical energy from an external alternating electromagnetic field and provide instantaneous operating power to the smart water meter terminal; A microcontroller is connected to the wireless power transmission module and the encoder. It is powered by the wireless power transmission module and controls the encoder to work and decode its output digital code to obtain the current water volume data after power-on reset. The external reading device includes an energy transmission and communication module for generating the external alternating electromagnetic field, sending downlink commands to the smart water meter terminal and receiving uplink data from the smart water meter terminal. The microcontroller responds to the downlink commands by returning a response frame containing the water consumption data to the external reading device through load modulation.

2. The wirelessly powered smart water meter direct reading system according to claim 1, characterized in that: The encoder includes a Gray code disk mounted on a mechanical character wheel and a photoelectric sensor array corresponding to the code track. The Gray code disk has a cyclic Gray code pattern consisting of light-transmitting and light-blocking areas corresponding to the position of the character wheel. The photoelectric sensor array includes an infrared emitting tube and an infrared receiving tube, which are used to generate light pulses and capture the state of the Gray code disk at the moment of power supply.

3. The wirelessly powered smart water meter direct reading system according to claim 2, characterized in that: The Gray code pattern on the Gray code disk is designed such that the codes of any two adjacent numbers differ by only one bit of binary digit; the photoelectric sensor array is sealed and encapsulated in a light-proof dark chamber.

4. The wirelessly powered smart water meter direct reading system according to claim 1, characterized in that: The communication between the smart water meter terminal and the external reading device includes: Downlink communication: The external reading device sends commands via amplitude shift keying modulated carrier wave, and the smart water meter terminal demodulates and decodes the commands via envelope detection circuit and comparator; Uplink communication: The smart water meter terminal controls the on / off state of the switching tubes connected in parallel across the induction coil to perform load modulation on the electromagnetic field generated by the external reading device, and returns data in frequency shift keying or phase shift keying mode.

5. The wirelessly powered smart water meter direct reading system according to claim 1, characterized in that: The wireless power transfer module includes: The energy receiving antenna uses a planar helical coil or a multi-layer PCB coil to sense external alternating electromagnetic fields. The parallel resonant circuit, consisting of a resonant capacitor connected in parallel with the energy receiving antenna, is used to increase the induced voltage. A rectifier circuit, consisting of Schottky diodes with low forward voltage drop, is a full-bridge rectifier circuit used to convert alternating current induced by a parallel resonant circuit into direct current.

6. The wirelessly powered smart water meter direct reading system according to claim 5, characterized in that: The wireless power transmission module further includes a power management unit, which includes: An energy storage element is connected to the output terminal of the rectifier circuit and is used to store electrical energy. The energy storage element is a double-layer supercapacitor. A linear regulator, connected to the energy storage element, is used to provide a stable voltage to the microcontroller; A voltage monitor, connected to the output of the linear regulator, is configured to: when the output voltage of the linear regulator does not reach a preset threshold, output a reset signal to the microcontroller to keep it in a reset state; and when the voltage reaches and stabilizes at the preset threshold, release the reset signal to allow the microcontroller to start working.

7. The wirelessly powered smart water meter direct reading system according to claim 3, characterized in that: The microcontroller reads the digital code from the encoder, specifically including the following steps: A short-time pulse current is supplied to the photoelectric emitter in the encoder to make it emit detection light; After the pulse ends, the states of all photodetectors are read in parallel to obtain the parallel Gray code representing the position of the character wheel; The parallel Gray code is converted into decimal numbers corresponding to each word wheel using an internally stored decoding table, and then synthesized into the final water consumption data.

8. The wirelessly powered smart water meter direct reading system according to claim 1, characterized in that: The energy transmission and communication module includes a high-frequency signal generator for generating a carrier signal of a predetermined frequency. The high-frequency signal generator is connected to a power amplifier for amplifying the carrier signal. The output of the power amplifier is connected to an impedance matching network. The impedance matching network is connected to a transmitting coil for generating the external alternating electromagnetic field based on the amplified carrier signal.

9. A wirelessly powered smart water meter direct reading system according to claim 8, characterized in that: The external reading device also includes a main controller, which is configured to perform the following steps: During the initial carrier transmission, the coupling field strength with the smart water meter terminal is sensed by detecting the current or voltage of the transmitting coil, and the output of the power amplifier is dynamically adjusted to make the field strength reach a preset working threshold. Uplink data reception steps: After sending downlink commands, monitor the changes in electrical parameters of the transmitting coil circuit to demodulate the uplink data sent back by the smart water meter terminal through load modulation.

10. A wirelessly powered smart water meter direct reading system according to claim 1, characterized in that: The external meter reading device also includes a human-machine interface and a data storage unit. The human-machine interface is used to display the meter reading status, water meter reading, and device information. The data storage unit is used to store meter reading records.

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