High-cost-performance soil humidity sensor for household gardening

Abstract

The utility model discloses a high cost performance soil humidity sensor for household gardening, which belongs to the technical field of detection sensors and comprises a shell, the bottom of the shell is connected with a PCB (printed circuit board) probe, the front surface of the PCB probe is an insulated electrode, the back surface of the PCB probe is a conductive electrode, and a 3.5 mm interface is arranged at the top of the shell; the shell is internally provided with an MCU chip and a discharge resistor, the insulation electrode is electrically connected with the MCU chip, the MCU chip is electrically connected with the discharge resistor, the discharge resistor is electrically connected with the conductive electrode, and the MCU chip is electrically connected with the 3.5 mm interface. The high-cost-performance soil humidity sensor for household gardening is simple in structure, low in manufacturing cost, high in measurement stability and measurement precision and capable of completely meeting the requirement for automatic control of household gardening equipment.

Description

Technical Field

[0001] The utility model relates to the technical field of detection sensors, in particular to a soil moisture sensor with high cost performance for home gardening. Background Art

[0002] With the popularity of home gardening, the demand for automated control of home gardening is also increasing. However, due to the high cost of soil moisture sensors that are used with automated equipment, home gardening equipment using automated control can only be used in high-end occasions and cannot be widely promoted to ordinary families. Some low-cost soil moisture sensors on the market cannot meet the requirements of measurement accuracy and stability of automated equipment due to their low accuracy and poor stability.

[0003] At present, commonly used soil moisture sensors can be divided into resistance sensors, TDR sensors, FDR sensors, and capacitance sensors according to their working principles. Among them, TDR sensors, FDR sensors, and capacitance sensors are also called dielectric sensors.

[0004] (1) Resistive soil moisture sensor

[0005] The working principle of a resistance sensor is to measure the percentage of soil moisture by creating a voltage difference between two electrodes, allowing a small amount of current to flow between the electrodes and calculating the resistance value or conductivity value. Since water is a very poor conductor, it is the ions in the water that carry the current from one electrode to the other. However, if the number of ions in the soil is not constant, the accuracy becomes very unreliable.

[0006] Therefore, the resistance sensor is cheap and can respond to the change of water content to a certain extent, which is suitable for some low-cost and low-precision occasions. However, in occasions with certain requirements for accuracy, it cannot meet the measurement accuracy requirements of water content.

[0007] (2) Capacitive soil moisture sensor

[0008] The capacitive soil moisture detection sensor detects soil moisture by measuring the change in capacitance in the soil. The soil capacitance value is approximately linearly related to the weight water content of the soil, and the accuracy is relatively high. However, this type of sensor generally has a complex electrode structure and mostly uses high-frequency detection technology, so the overall cost is relatively high and the accuracy is not as good as TDR and FDR sensors. Therefore, it cannot be widely promoted and applied.

[0009] (3) TDR soil moisture sensor (time domain sensor)

[0010] The measurement principle of the TDR sensor is to measure the propagation time of the reflected wave of electric energy along the transmission line. The travel time is related to the charge storage capacity and volumetric water content of the soil. In addition, TDR includes a series of frequencies in the signal (not just a single frequency), which helps to reduce the error caused by soil salinity. The disadvantages of TDR sensors are that they are more complex than circuit structures, high cost, and high power consumption.

[0011] (4) FDR soil moisture sensor (frequency domain sensor)

[0012] The measurement principle of FDR sensor is to use soil as a capacitor to measure the maximum resonant frequency in the circuit, and the resonant frequency is related to the water content. Compared with TDR sensor, the measurement time is shorter, and the probe shape is not restricted. It can measure multiple depths simultaneously, and the measurement results are easier to collect. The disadvantage of TDR sensor is that the circuit structure is complex and the cost is high.

[0013] In the above schemes, the accuracy and stability of resistive sensors are very poor and cannot meet the requirements of measurement accuracy; the electrode structure of capacitive soil moisture sensors is complex and the cost is high, making them difficult to promote and apply; TDR and FDR measurement accuracy is very high, but due to their high cost, they can only be used in large-scale agricultural planting projects and are not suitable for automatic control of home gardening. Utility Model Content

[0014] The utility model aims to provide a soil moisture sensor with high cost performance for home gardening, which has simple structure, low manufacturing cost, high measurement stability and measurement accuracy, and can fully meet the requirements of automated control of home gardening equipment.

[0015] To achieve the above-mentioned purpose, the utility model provides a cost-effective soil moisture sensor for home gardening, comprising a shell, a PCB board probe is connected to the bottom of the shell, the front of the PCB board probe is an insulating electrode, the back of the PCB board probe is a conductive electrode, and a 3.5mm interface is opened on the top of the shell; an MCU chip and a discharge resistor are installed inside the shell, the insulating electrode is electrically connected to the MCU chip, the MCU chip is electrically connected to the discharge resistor, the discharge resistor is electrically connected to the conductive electrode, and the MCU chip is electrically connected to the 3.5mm interface.

[0016] Preferably, an MCU external clock unit electrically connected to the MCU chip is arranged inside the shell.

[0017] Preferably, the MCU external clock unit is an external crystal oscillator.

[0018] Preferably, the middle part of the PCB probe is a hollow structure, the bottom is open, and the whole is an inverted U-shape; both sides of the front side of the PCB probe are insulating electrodes, and both sides of the back side are conductive electrodes.

[0019] Preferably, the bottom of the PCB board probe is an inverted cone structure.

[0020] Preferably, the MCU chip internally comprises an electronic switch module, a pulse generating module, an AD conversion module, a digital filtering module, a humidity value calibration and numerical conversion module and a serial data output module; the insulated electrode is connected to the electronic switch module, the electronic switch module is respectively connected to the pulse generating module and the discharge resistor, the acquisition end of the AD conversion module is connected between the electronic switch module and the discharge resistor, the output end of the AD conversion module is connected to the input end of the digital filtering module, the output end of the digital filtering module is connected to the input end of the humidity value calibration and numerical conversion module, the output end of the humidity value calibration and numerical conversion module is connected to the input end of the serial data output module, and the output end of the serial data output module is connected to the 3.5 mm interface.

[0021] Therefore, the utility model adopts the above-mentioned cost-effective soil moisture sensor for home gardening, which has a simple structure, low manufacturing cost, high measurement stability and measurement accuracy, and can fully meet the requirements of automated control of home gardening equipment.

[0022] The technical solution of the utility model is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a front view schematic diagram of an embodiment of a soil moisture sensor with high cost performance for home gardening of the utility model;

[0024] Figure 2 It is a rear view schematic diagram of an embodiment of a cost-effective soil moisture sensor for home gardening of the utility model;

[0025] Figure 3 This is a circuit structure principle diagram of an embodiment of a high cost-effective soil moisture sensor for home gardening of the utility model;

[0026] Figure 4 It is an equivalent diagram of the electronic switch module circuit of the utility model.

[0027] Reference numerals

[0028] 1. Shell; 2. PCB board probe; 3. Insulated electrode; 4. Conductive electrode; 5. 3.5mm interface; 6. MCU chip; 7. Discharge resistor; 8. MCU external clock unit. DETAILED DESCRIPTION

[0029] The technical solution of the utility model is further described below through the accompanying drawings and embodiments.

[0030] Unless otherwise defined, the technical terms or scientific terms used in the present invention shall have the usual meanings understood by persons with ordinary skills in the field to which the present invention belongs. The words "first", "second" and similar words used in the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. Words such as "include" or "comprise" and the like mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. Words such as "connect" or "connected" and the like are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0031] Embodiment 1

[0032] like Figure 1 As shown, the utility model provides a cost-effective soil moisture sensor for home gardening, comprising a housing 1, a PCB probe 2 connected to the bottom of the housing 1, the PCB probe 2 is a hollow structure in the middle, and an opening at the bottom, and is in an inverted U shape as a whole, so that the PCB probe 2 is convenient to be inserted into the soil to detect soil moisture.

[0033] like Figure 1 and Figure 2 As shown, the front side of the PCB probe 2 is provided with two insulating electrodes 3, and the back side is provided with two conductive electrodes 4. The two insulating electrodes 3 on the front side form a capacitor with the soil medium, and the two conductive electrodes 4 on the back side connect the soil to the ground wire of the detection circuit, which can prevent the interference signal sensed by the soil from entering the detection circuit. The bottom sides of the PCB probe 2 are both inverted conical structures, which can further facilitate the insertion of the PCB probe 2 into the soil for soil moisture detection.

[0034] The top of the housing 1 is provided with a 3.5 mm interface 5 for data transmission and power supply to the MCU chip 6. The MCU chip 6 and the discharge resistor 7 are installed inside the housing 1, the insulating electrode 3 is electrically connected to the MCU chip 6, the MCU chip 6 is electrically connected to the discharge resistor 7, the discharge resistor 7 is electrically connected to the conductive electrode 4, and the MCU chip 6 is electrically connected to the 3.5 mm interface 5.

[0035] like Figure 3 As shown, the MCU chip 6 includes an electronic switch module, a pulse generation module, an AD conversion module, a digital filter module, a humidity value calibration and value conversion module and a serial data output module. The equivalent diagram of the electronic switch module circuit is shown in FIG. Figure 4As shown, the pulse generation module is a programmable timer inside the MCU chip 6, the AD conversion module is an AD conversion interface inside the MCU chip 6, the serial data output module is an internal serial interface inside the MCU chip 6, and the digital filtering module and the humidity value calibration and numerical conversion module are all implemented by the internal software algorithm of the MCU chip 6.

[0036] The insulated electrode 3 is connected to the electronic switch module, and the electronic switch module is respectively connected to the pulse generating module and the discharge resistor. When the insulated electrode 3 is connected to the pulse generating module through the electronic switch module, the detection circuit can be in a charging cycle. When the insulated electrode 3 is connected to the discharge resistor through the electronic switch module, the detection circuit can be in a discharging cycle.

[0037] The acquisition end of the AD conversion module is connected between the electronic switch module and the discharge resistor, and is used to collect the discharge voltage during the discharge cycle. The output end of the AD conversion module is connected to the input end of the digital filter module. The collected voltage value is digitally filtered by the digital filter module to filter out interference signals. The output end of the digital filter module is connected to the input end of the humidity value calibration and numerical conversion module, and the filtered voltage value can be linearly calibrated and converted into a humidity value of 0-100%. The output end of the humidity value calibration and numerical conversion module is connected to the input end of the serial data output module, and the output end of the serial data output module is connected to the 3.5mm interface, which can convert the humidity value into serial data and output it.

[0038] An MCU external clock unit 8 electrically connected to the MCU chip 6 is provided inside the shell 1. The MCU external clock unit 8 is an external crystal oscillator with high clock accuracy. It can calibrate the timer inside the MCU chip 6 and provide a high-precision clock signal for the MCU chip 6, which can effectively improve the detection accuracy of the sensor.

[0039] The working principle is as follows: the utility model uses a PCB circuit board as a probe, and the circuit can realize all detection functions by a MCU chip 6. The front of the PCB probe 2 is two insulating electrodes 3 that form a capacitor with the soil medium, and the back is two conductive electrodes 4 that connect the soil to the ground wire of the detection circuit to prevent the interference signal sensed by the soil from entering the detection circuit.

[0040] The detection circuit is divided into a charging cycle and a discharging cycle. When the electronic switch module is connected to the pulse generating module inside the MCU chip 6, the detection circuit is in the charging cycle. The pulse generating module is a programmable timer inside the MCU chip 6, which can generate a charging pulse to charge the capacitor electrode formed by the insulating electrode 3 and the soil medium. Since the capacitor electrode is directly connected to the pulse, the capacitor can be fully charged instantly.

[0041] Then, the electronic switch module connects the discharge resistor 7, and the detection circuit enters the discharge cycle. During the discharge cycle, the MCU chip 6 continuously collects the discharge voltage through the AD conversion module, and starts the internal timer of the MCU chip 6 to record the time required for the discharge voltage to reach a predetermined value. The time required for different capacitors to discharge to a predetermined voltage value is also different. Since the capacitance value changes with the change of soil moisture, the discharge time also represents the soil moisture value. The collected voltage value is filtered by the digital filter module to filter out interference signals. Finally, the MCU chip 6 linearizes the collected and filtered voltage value and converts it into a humidity value of 0-100%. In order to further improve the anti-interference ability of the sensor, the humidity value is directly output from the serial interface to the controller through the serial data output module, which can effectively avoid interference during the transmission process. At the same time, in order to ensure the accuracy of the sensor, the MCU chip 6 is externally connected to an external crystal oscillator as a clock source.

[0042] Therefore, the utility model adopts the above-mentioned cost-effective soil moisture sensor for home gardening, which has a simple structure, low manufacturing cost, high measurement stability and measurement accuracy, and can fully meet the requirements of automated control of home gardening equipment.

[0043] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the utility model rather than to limit it. Although the utility model has been described in detail with reference to the preferred embodiments, ordinary technicians in this field should understand that they can still modify or replace the technical solution of the utility model with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the utility model.

Claims

1. A cost-effective soil moisture sensor for home gardening, characterized by: It comprises a shell, a PCB probe is connected to the bottom of the shell, the front of the PCB probe is an insulating electrode, the back of the PCB probe is a conductive electrode, and a 3.5mm interface is opened on the top of the shell; an MCU chip and a discharge resistor are installed inside the shell, the insulating electrode is electrically connected to the MCU chip, the MCU chip is electrically connected to the discharge resistor, the discharge resistor is electrically connected to the conductive electrode, and the MCU chip is electrically connected to the 3.5mm interface.

2. A cost-effective soil moisture sensor for home gardening according to claim 1, characterized in that: An MCU external clock unit electrically connected to the MCU chip is arranged inside the shell.

3. A cost-effective soil moisture sensor for home gardening according to claim 2, characterized in that: The MCU external clock unit is an external crystal oscillator.

4. The cost-effective soil moisture sensor for home gardening according to claim 1, characterized in that: The PCB probe has a hollow structure in the middle and an opening at the bottom, and is in an inverted U shape as a whole; both sides of the front of the PCB probe are insulating electrodes, and both sides of the back are conductive electrodes.

5. The cost-effective soil moisture sensor for home gardening according to claim 1, characterized in that: The bottom of the PCB probe is an inverted cone structure.

6. The cost-effective soil moisture sensor for home gardening according to claim 1, characterized in that: The MCU chip internally includes an electronic switch module, a pulse generating module, an AD conversion module, a digital filter module, a humidity value calibration and numerical conversion module and a serial data output module; the insulated electrode is connected to the electronic switch module, the electronic switch module is respectively connected to the pulse generating module and the discharge resistor, the acquisition end of the AD conversion module is connected between the electronic switch module and the discharge resistor, the output end of the AD conversion module is connected to the input end of the digital filter module, the output end of the digital filter module is connected to the input end of the humidity value calibration and numerical conversion module, the output end of the humidity value calibration and numerical conversion module is connected to the input end of the serial data output module, and the output end of the serial data output module is connected to the 3.5mm interface.

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