A method of detecting soil moisture
Soil moisture is directly obtained through a simplified circuit structure. By using a waveform generator, phase detector, and differential amplifier to replace the circulator and coaxial cable, the problems of hardware complexity and high cost in the existing technology are solved, and efficient and low-cost soil moisture detection is achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- HEBEI LEIDEN ELECTRONIC TECHNOLOGY CO LTD
- Filing Date
- 2026-04-27
- Publication Date
- 2026-07-21
AI Technical Summary
Existing phase-based soil moisture detection technology relies on specialized high-frequency devices such as circulators and coaxial cables, resulting in complex hardware structures, high costs, and difficult debugging.
The signal processing circuit is composed of a waveform generator, a first phase detector, a second phase detector, and a differential amplifier. It directly acquires the phase difference between the transmitted and reflected signals and converts it into a differential voltage. The acquisition and processing are performed by a microcontroller, replacing the traditional circulator and coaxial cable.
It simplifies the system structure, reduces hardware costs and debugging difficulty, while ensuring the sensitivity and accuracy of phase detection, making it suitable for low-cost and easily integrated soil moisture detection applications.
Smart Images
Figure CN122430401A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of soil testing technology, and more particularly to a method for detecting soil moisture. Background Technology
[0002] Current phase-based soil moisture detection technology typically uses a long steel needle connected to a signal transmitter via a 50-ohm coaxial cable. A circulator and delay cable are required to synchronize the signal propagation time between the circulator and the steel needle. The circulator separates the transmitted signal to the sensor probe from its reflected signal. This approach not only relies on specialized high-frequency components such as circulators and coaxial cables, resulting in complex hardware and high costs, but also requires extensive software calculations to obtain the phase difference, making system debugging difficult and unsuitable for large-scale deployment or cost-sensitive applications. Summary of the Invention
[0003] This invention proposes a method for detecting soil moisture, which solves the problem that existing phase-based soil moisture detection technologies rely on dedicated high-frequency devices such as circulators and coaxial cables, resulting in complex hardware structures, high costs, and difficult debugging.
[0004] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: A method for detecting soil moisture includes the following steps: S1. Signal generation steps: A high-frequency electrical signal is generated by a waveform generator U4 located in the signal processing circuit; S2. Signal transmission and reception steps: The high-frequency electrical signal is transmitted to the detection steel needle inserted in the soil through an inductor L1 and transmitted, while the reflected signal returned from the detection steel needle after being acted upon by the soil is received. S3. Phase difference extraction step: The signal generated by the waveform generator U4 is used as a reference signal and input to the first phase detector U6; the reflected signal obtained from the node between the inductor L1 and the probe needle is input to the second phase detector U5; the output signals of the first phase detector U6 and the second phase detector U5 are input to a differential amplifier U2 for differential amplification to obtain a differential voltage signal characterizing the phase difference between the reference signal and the reflected signal; S4. Signal processing and output steps: The differential voltage signal output by the differential amplifier U2 is acquired by a single-chip microcomputer processor U1, and the soil moisture value is determined based on the differential voltage signal.
[0005] Furthermore, in step S4, the microcontroller processor U1 pre-stores the correspondence data between differential voltage signals and soil moisture. The step of determining the moisture value includes: comparing the collected differential voltage signal with the correspondence data to obtain the corresponding soil moisture value.
[0006] Furthermore, the signal processing circuit includes: The power conversion module is used to convert the externally input DC voltage into the VCC_3.3V operating voltage required by the internal circuit. The waveform generator U4 has its CLK pin connected to the clock output pin of the microcontroller processor U1, and its OUT pin used as a signal output terminal. The inductor L1 has one end connected to the OUT pin of the waveform generator U4 and the other end connected to the probe needle. The first phase detector U6 has its Sign Input pin connected to the OUT pin of the waveform generator U4 to receive a reference signal, its power supply pin and ground pin connected to VCC_3.3V power supply and ground respectively, and its OUT pin as an output; The second phase detector U5 has its Sign Input pin connected to the node between the inductor L1 and the probe needle to receive the reflected signal, its power supply pin and ground pin connected to VCC_3.3V power supply and ground respectively, and its OUT pin as the output; The differential amplifier U2 has two differential input pins connected to the OUT pins of the first phase detector U6 and the second phase detector U5, respectively, and its output pin is connected to the analog-to-digital conversion input pin of the microcontroller processor U1. The microcontroller processor U1 is used to control the waveform generator U4 and process the differential voltage signal.
[0007] Furthermore, the waveform generator U4 is a programmable clock chip, and its enable pin EN is connected to the general-purpose input / output pin of the microcontroller processor U1, and its working state is controlled by the microcontroller processor U1.
[0008] Furthermore, the first phase detector U6 and the second phase detector U5 are integrated phase detection chips with the same model and parameters. Their VCC pins are both connected to the VCC_3.3V operating voltage, and their GND pins are both grounded.
[0009] Furthermore, an RC low-pass filter circuit consisting of resistors and capacitors is connected between the output pin of the differential amplifier U2 and the analog-to-digital conversion input pin of the microcontroller processor U1.
[0010] Furthermore, the microcontroller U1 is also connected to a temperature sensor interface, which includes a temperature signal line ADC_TEMP connected to the analog-to-digital conversion pin of the microcontroller U1 and a sensor power control line TEMP_PWR controlled by the control pin of the microcontroller U1; in step S4, the microcontroller U1 also acquires soil temperature data through the temperature sensor interface and performs temperature compensation on the determined humidity value.
[0011] Furthermore, the microcontroller processor U1 is connected to a communication module U3, which is used to transmit the determined soil moisture value to the outside; the power supply pin of the communication module U3 is connected to the VCC_3.3V operating voltage.
[0012] Furthermore, the communication module U3 is an RS-485 bus transceiver, whose data input pin DI and data output pin RO are respectively connected to the serial communication interfaces TX and RX of the microcontroller processor U1, and its bus interface includes pins A and B.
[0013] Furthermore, the entire signal processing circuit is integrated into a housing, and the probe needle is connected to the circuit inside the housing via a wire to form an independent soil moisture detection terminal; the housing is provided with an interface for connecting an external power supply and a communication bus.
[0014] The positive effects of this invention are as follows: By designing a pure circuit-based phase difference detection scheme, it replaces the traditional circulator and coaxial cable structure. Specifically, a signal processing circuit is constructed using a waveform generator, a first phase detector, a second phase detector, and a differential amplifier to directly acquire the phase difference between the transmitted and reflected signals and convert it into a differential voltage, which is then acquired and processed by a microcontroller. This method eliminates the need for dedicated components such as circulators and delay cables, and avoids complex software phase calculations, thereby significantly simplifying the system structure, reducing hardware costs and debugging difficulty, while ensuring the sensitivity and accuracy of phase detection. It is more suitable for soil moisture detection applications requiring low cost and easy integration. Attached Figure Description
[0015] Figure 1 This is a first principle block diagram of the method for detecting soil moisture according to the present invention; Figure 2 This is a second principle block diagram of the method for detecting soil moisture in this invention; Figure 3 This is a circuit diagram of the first part of the method for detecting soil moisture in a specific embodiment of the present invention; Figure 4 This is a circuit diagram of the second part of the method for detecting soil moisture in a specific embodiment of the present invention; Figure 5 This is the third part of the circuit diagram for implementing the method for detecting soil moisture in a specific embodiment of the present invention; Figure 6 This is the fourth part of the circuit diagram for implementing the method of detecting soil moisture in a specific embodiment of the present invention. Detailed Implementation
[0016] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.
[0017] Example Combination Figure 1-6 As shown, a method for detecting soil moisture includes the following steps: S1. Signal generation step: A waveform generator U4 in a signal processing circuit generates a high-frequency electrical signal; S2. Signal transmission and reception step: The high-frequency electrical signal is transmitted to a probe inserted into the soil via an inductor L1 and transmitted, while the reflected signal returned from the probe after being acted upon by the soil is received; S3. Phase difference extraction step: The signal generated by the waveform generator U4 is used as a reference signal and input to a first phase detector U6; the reflected signal obtained from the node between the inductor L1 and the probe is input to a second phase detector U5; the output signals of the first phase detector U6 and the second phase detector U5 are input to a differential amplifier U2 for differential amplification to obtain a differential voltage signal characterizing the phase difference between the reference signal and the reflected signal; S4. Signal processing and output step: A microcontroller U1 acquires the differential voltage signal output by the differential amplifier U2 and determines the soil moisture value based on the differential voltage signal.
[0018] In step S4, the microcontroller processor U1 pre-stores the correspondence data between differential voltage signals and soil moisture. The step of determining the moisture value includes: comparing the collected differential voltage signal with the correspondence data to obtain the corresponding soil moisture value.
[0019] The signal processing circuit includes: a power conversion module for converting externally input DC voltage into the VCC_3.3V operating voltage required internally by the circuit; a waveform generator U4, whose CLK pin is connected to the clock output pin of the microcontroller processor U1, and whose OUT pin serves as the signal output terminal; an inductor L1, one end of which is connected to the OUT pin of the waveform generator U4, and the other end of which is connected to the probe needle; a first phase detector U6, whose Sign Input pin is connected to the OUT pin of the waveform generator U4 to receive a reference signal, whose power supply pin and ground pin are respectively connected to the VCC_3.3V power supply and ground, and whose OUT pin serves as the output; and a second phase detector U5 ... and ground pin are connected to the OUT pin of the waveform generator U4 to receive a reference signal, whose power supply pin and ground pin are respectively connected to the VCC_3.3V power supply and ground, and whose OUT pin serves as the output; and a second phase detector U5, whose Sign Input pin and ground pin are connected to the OUT pin of the waveform generator U4 to receive a reference signal, whose power supply pin and ground pin are respectively connected to the VCC_3.3V power supply and ground, and whose OUT pin serves as the output; and a second The input pin is connected to the node between the inductor L1 and the probe needle to receive the reflected signal. Its power supply pin and ground pin are connected to the VCC_3.3V power supply and ground, respectively. Its OUT pin serves as the output. The differential amplifier U2 has two differential input pins connected to the OUT pins of the first phase detector U6 and the second phase detector U5, respectively. Its output pin is connected to the analog-to-digital conversion input pin of the microcontroller U1. The microcontroller U1 is used to control the waveform generator U4 and process the differential voltage signal.
[0020] The waveform generator U4 is a programmable clock chip, and its enable pin EN is connected to the general-purpose input / output pin of the microcontroller U1, which controls its operating state. The first phase detector U6 and the second phase detector U5 are integrated phase detection chips with the same model and parameters. Their VCC pins are both connected to the VCC_3.3V operating voltage, and their GND pins are both grounded. An RC low-pass filter circuit composed of resistors and capacitors is connected between the output pin of the differential amplifier U2 and the analog-to-digital converter input pin of the microcontroller U1. The microcontroller U1 is also connected to a temperature sensor interface, which includes a temperature signal line ADC_TEMP connected to the analog-to-digital converter pin of the microcontroller U1 and a sensor power control line TEMP_PWR controlled by the control pin of the microcontroller U1. In step S4, the microcontroller U1 also acquires soil temperature data through the temperature sensor interface and performs temperature compensation on the determined humidity value.
[0021] The microcontroller processor U1 is connected to a communication module U3 for transmitting the determined soil moisture value. The power supply pin of the communication module U3 is connected to the VCC_3.3V operating voltage. The communication module U3 is an RS-485 bus transceiver, and its data input pin DI and data output pin RO are respectively connected to the serial communication interface TX and RX of the microcontroller processor U1. Its bus interface includes pins A and B. The entire signal processing circuit is integrated into a housing. The probe is connected to the circuit inside the housing via a wire, forming an independent soil moisture detection terminal. The housing has an interface for connecting an external power supply and a communication bus.
[0022] The following is in conjunction with the appendix Figure 1-6 The method for detecting soil moisture provided by the present invention will be described in detail below with specific embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of protection of the present invention.
[0023] The core of this invention lies in providing a convenient circuit solution that replaces the circulator and coaxial cable in the traditional long steel needle phase difference method. Through an innovative circuit structure, the phase difference between the transmitted signal and the reflected signal returned from the soil can be obtained directly and efficiently, thereby calculating the soil moisture.
[0024] System Overall Composition: The soil moisture detection system provided in this embodiment mainly includes: a power conversion module, a waveform generator, a probe steel needle, a first phase detector, a second phase detector, a differential amplifier, a microcontroller processor, and a communication module. These components are connected by circuitry and work together.
[0025] Working principle: The entire method follows a logical sequence of signal generation, transmission, reception, processing, and output, as detailed below: System Power-On and Initialization: An external DC power supply (e.g., 9-24V) is connected to the system's power conversion module. This module first stabilizes the input voltage to +5V, and then generates a stable VCC_3.3V (+3.3V) operating voltage through a low-dropout linear regulator. This voltage powers all active components in the system, including the waveform generator U4, the first phase detector U6, the second phase detector U5, the differential amplifier U2, the microcontroller U1, and the communication module U3. After the system powers on, the microcontroller U1 completes program initialization, configuring the internal clock, analog-to-digital converter (ADC), serial communication interface, and other peripheral devices.
[0026] High-frequency signal generation and transmission: The microcontroller processor U1 provides a reference clock to the CLK pin of the waveform generator U4 through its clock output pin, and controls the enable (EN) pin of U4 through a general purpose input / output (GPIO) pin to start U4's operation. The waveform generator U4 (e.g., a programmable clock chip) generates a high-frequency, stable sine wave or square wave electrical signal of a specific frequency (e.g., several hundred MHz) on its OUT pin according to a preset configuration, as a transmission signal for detection.
[0027] The transmitted signal is transmitted through an inductor L1 to a long steel needle (probe needle) directly inserted into the soil being tested. Inductor L1 serves to match impedance and couple the signal. The transmitted signal radiates through the steel needle into the surrounding soil medium.
[0028] Reflected signal reception and reference signal acquisition: When the transmitted signal propagates in the soil, its propagation characteristics (such as phase) are affected by the soil dielectric constant, which is closely related to the water content (humidity). Part of the signal energy is absorbed by the soil, while the other part forms a reflected signal that returns along the original path and is received by the steel needle. Simultaneously, the system needs to acquire a clean, unaffected reference signal for comparison. The key circuit design of this invention is embodied here: Reference signal path: The original transmit signal output from the OUT pin of waveform generator U4 is directly led to the Sign Input pin of the first phase detector U6. This signal serves as the reference signal for phase comparison.
[0029] Reflected signal path: The reflected signal returning from the steel needle is led to the Sign Input pin of the second phase detector U5 via the connection node between inductor L1 and the steel needle. This signal contains information about the phase change caused by soil moisture.
[0030] Phase difference to voltage conversion (core detection step): The first phase detector U6 and the second phase detector U5 are integrated phase detection chips with identical models and parameters. Their function is to convert the phase information of the input signal into a proportional DC voltage signal. U6 detects the reference signal input to its Sign Input pin and outputs a DC voltage V_ref related to the phase of the reference signal at its OUT pin. U5 detects the reflected signal input to its Sign Input pin and outputs a DC voltage V_refl related to the phase of the reflected signal at its OUT pin. Because the reflected signal has a phase delay relative to the reference signal (this delay ΔΦ is related to soil moisture), there is a difference between V_refl and V_ref. These two voltage signals, V_ref and V_refl, are respectively fed into the two differential input pins of the differential amplifier U2 (such as the inverting input and the non-inverting input). The differential amplifier U2 differentially amplifies these two voltages, that is, amplifies (V_refl - V_ref) or (V_ref - V_refl). Its output pin ultimately generates a single, amplified differential voltage signal V_diff. The magnitude of this V_diff signal directly and linearly reflects the phase difference ΔΦ between the reference signal and the reflected signal, thus indirectly reflecting the dielectric constant of the soil, i.e., soil moisture.
[0031] Signal processing and humidity calculation: The analog voltage signal V_diff output by the differential amplifier U2 usually passes through an RC low-pass filter circuit composed of resistors and capacitors before being transmitted to the ADC input pin of the microcontroller processor U1, in order to filter out high-frequency noise and improve the signal-to-noise ratio.
[0032] The microcontroller processor U1 periodically acquires the filtered V_diff voltage value through its built-in ADC. The processor U1 has a pre-stored data table or calculation formula (algorithm model) of the correspondence between "differential voltage V_diff - soil volumetric water content θ" obtained through calibration and experiments.
[0033] The processor U1 compares or calculates the collected real-time V_diff value with the internally stored correspondence to obtain the current soil moisture value. To improve accuracy, the processor U1 can also read data from an external soil temperature sensor through its dedicated temperature sensor interface (such as connecting the ADC_TEMP signal line and controlling the TEMP_PWR power line), and compensate and correct the calculated moisture value according to the temperature to eliminate the influence of temperature.
[0034] Results and Applications: The calculated soil moisture value can be sent by the microcontroller processor U1 to the communication module U3 (e.g., an RS-485 bus transceiver) via its serial communication interface (TX, RX). U3 converts the processor signal into a differential signal and connects it to the RS-485 bus network through its A and B pins.
[0035] Humidity data can be sent to remote host computer monitoring software, program controllers (such as irrigation controllers), or other data acquisition devices to achieve remote monitoring of soil moisture, automated irrigation control, or early warning of geological disasters (landslides, debris flows), etc. The entire signal processing circuit can be integrated and packaged in a waterproof housing, forming an independent handheld or buried soil moisture detection terminal together with a detachable steel needle.
[0036] This invention, through the specific embodiments described above, achieves a simple, low-cost pure circuit solution (waveform generator, two phase detectors, and differential amplifier) that replaces the expensive and complex circulator and 50-ohm coaxial cable required in traditional phase-based soil moisture detection. This solution avoids circulator design, delay cable matching, and complex software phase calculations, simplifying the system structure, reducing hardware costs and debugging difficulty, while ensuring the sensitivity and accuracy of phase difference detection. It is particularly suitable for applications requiring large-scale deployment or cost-sensitive scenarios.
[0037] Experimental Record: According to the test method of GB / T50123-2019, the drying method was adopted. A 120g sample was taken by ring cutting and recorded as W1. It was placed in a drying oven with a set temperature of 110℃ and a drying time of 8 hours until constant weight was reached (the two weighings did not exceed the specified value). After cooling, the weight was weighed W2. The moisture content was calculated as (W1-W2 / W2)*100. The experimental results are shown in the table below.
[0038] The above-described embodiments are detailed and specific, illustrating preferred embodiments of the present invention. They are only used to illustrate the technical ideas and features of the present invention, with the aim of enabling those skilled in the art to understand the content of the present invention and implement it accordingly. However, they are not limited to the present invention, and the patent scope of the present invention cannot be limited by this embodiment alone. That is, any equivalent changes or modifications made to the spirit disclosed in the present invention, without departing from the structure of the present invention, such as local improvements within the system and modifications or transformations between subsystems, are still within the patent scope of the present invention.
Claims
1. A method for detecting soil moisture, characterized in that, Includes the following steps: S1. Signal generation steps: A high-frequency electrical signal is generated by a waveform generator (U4) located in the signal processing circuit; S2. Signal transmission and reception steps: The high-frequency electrical signal is transmitted to the detection steel needle inserted in the soil through an inductor (L1) and transmitted, while the reflected signal returned from the detection steel needle after being acted upon by the soil is received. S3. Phase difference extraction step: The signal generated by the waveform generator (U4) is used as a reference signal and input to the first phase detector (U6); the reflected signal obtained from the node between the inductor (L1) and the probe needle is input to the second phase detector (U5); the output signals of the first phase detector (U6) and the second phase detector (U5) are input to a differential amplifier (U2) for differential amplification to obtain a differential voltage signal characterizing the phase difference between the reference signal and the reflected signal; S4. Signal processing and output steps: The differential voltage signal output by the differential amplifier (U2) is acquired by a single-chip microcomputer processor (U1), and the soil moisture value is determined based on the differential voltage signal.
2. The method for detecting soil moisture according to claim 1, characterized in that, In step S4, the microcontroller processor (U1) pre-stores the correspondence data between differential voltage signals and soil moisture. The step of determining the moisture value includes: comparing the collected differential voltage signal with the correspondence data to obtain the corresponding soil moisture value.
3. The method for detecting soil moisture according to claim 1, characterized in that, The signal processing circuit includes: The power conversion module is used to convert the externally input DC voltage into the VCC_3.3V operating voltage required by the internal circuit. The waveform generator (U4) has its CLK pin connected to the clock output pin of the microcontroller processor (U1), and its OUT pin used as a signal output terminal. The inductor (L1) has one end connected to the OUT pin of the waveform generator (U4) and the other end connected to the probe needle; The first phase detector (U6) has its Sign Input pin connected to the OUT pin of the waveform generator (U4) to receive a reference signal, its power supply pin and ground pin connected to VCC_3.3V power supply and ground respectively, and its OUT pin as an output; The second phase detector (U5) has its Sign Input pin connected to the node between the inductor (L1) and the probe needle to receive the reflected signal, its power supply pin and ground pin connected to VCC_3.3V power supply and ground respectively, and its OUT pin as the output; The differential amplifier (U2) has two differential input pins connected to the OUT pins of the first phase detector (U6) and the second phase detector (U5) respectively, and its output pin is connected to the analog-to-digital conversion input pin of the microcontroller processor (U1). The microcontroller processor (U1) is used to control the waveform generator (U4) and process the differential voltage signal.
4. The method for detecting soil moisture according to claim 3, characterized in that, The waveform generator (U4) is a programmable clock chip, and its enable pin (EN) is connected to the general-purpose input / output pin of the microcontroller processor (U1), and its working state is controlled by the microcontroller processor (U1).
5. The method for detecting soil moisture according to claim 3, characterized in that, The first phase detector (U6) and the second phase detector (U5) are integrated phase detection chips with the same model and parameters. Their VCC pins are both connected to the VCC_3.3V operating voltage, and their GND pins are both grounded.
6. The method for detecting soil moisture according to claim 3, characterized in that, An RC low-pass filter circuit consisting of resistors and capacitors is connected between the output pin of the differential amplifier (U2) and the analog-to-digital conversion input pin of the microcontroller processor (U1).
7. The method for detecting soil moisture according to claim 3, characterized in that, The microcontroller processor (U1) is also connected to a temperature sensor interface, which includes a temperature signal line (ADC_TEMP) connected to the analog-to-digital conversion pin of the microcontroller processor (U1) and a sensor power control line (TEMP_PWR) controlled by the control pin of the microcontroller processor (U1); in step S4, the microcontroller processor (U1) also acquires soil temperature data through the temperature sensor interface and performs temperature compensation on the determined humidity value.
8. The method for detecting soil moisture according to claim 3, characterized in that, The microcontroller processor (U1) is connected to a communication module (U3) for transmitting the determined soil moisture value to the outside; the power supply pin of the communication module (U3) is connected to the VCC_3.3V operating voltage.
9. A method for detecting soil moisture according to claim 8, characterized in that, The communication module (U3) is an RS-485 bus transceiver. Its data input pin (DI) and data output pin (RO) are respectively connected to the serial communication interface (TX, RX) of the microcontroller processor (U1). Its bus interface includes pin A and pin B.
10. A method for detecting soil moisture according to claim 3, characterized in that, The entire signal processing circuit is integrated into a housing. The probe is connected to the circuit inside the housing via a wire to form an independent soil moisture detection terminal. The housing is provided with an interface for connecting an external power supply and a communication bus.