Soil moisture sensor

• US 9,804,113 B2
• Filed: 05/18/2015
• Issued: 10/31/2017
• Est. Priority Date: 05/19/2014
• Status: Active Grant

• Current Assignee: Fiskars Oyj Abp
• Original Assignee: Fiskars Oyj Abp
• Inventors: Kumaran, Hari Hara, Tomar, Vibha
• Primary Examiner(s): Hollington, Jermele M
• Assistant Examiner(s): Rajaputra, Suresh K
• Application Number:
  US14/715,352
• Publication Number:
  US 20150330932A1
• Time in Patent Office: 897 Days
• CPC Class Codes: A01G 25/167 Control by humidity of the soil itself or of devices simulating soil or of the atmosphere; Soil humidity sensors
• CPC Class Codes: G01N 27/221 by investigating the dielectric properties using microwaves G01N22/00; measuring loss factors or dielectric constants per se G01R27/26
• CPC Class Codes: G01N 27/223 for determining moisture content, e.g. humidity rain detectors on vehicle windows B60S1/0825

Abstract

A soil moisture sensor includes a capacitive probe configured to be inserted into soil, a series RLC circuit electrically coupled to the capacitive probe, a microcontroller configured to determine the capacitance value of the soil and determine the moisture content of the soil from the capacitance value of the soil.

Claims

1. A soil moisture sensor, comprising:

a capacitive probe configured to be inserted into soil;

a series RLC circuit electrically coupled to the capacitive probe; and

a microcontroller configured to

provide a drive signal having a predetermined drive signal frequency to the series RLC circuit,

receive an output signal including one of an output voltage or an output current from the capacitive probe,

determine the capacitance value of the soil based at least in part on the received output signal, and

determine the moisture content of the soil based on the determined capacitance value.

2. The soil moisture sensor of claim 1, wherein the capacitive probe comprises two electrodes.

3. The soil moisture sensor of claim 2, wherein each electrode comprises a pointed tip configured for insertion into soil.

4. The soil moisture sensor of claim 2, wherein the two electrodes form a parallel plate capacitor.

5. The soil moisture sensor of claim 1, wherein the drive signal frequency is selected with reference to a resonance curve of the series RLC circuit.

6. The soil moisture sensor of claim 1, where the drive signal frequency is selected to fall on the falling edge of the resonance curve of the series RLC circuit.

7. The soil moisture sensor of claim 1, wherein the drive signal frequency is less than 1 MHz.

8. The soil moisture sensor of claim 1, wherein the drive signal frequency is between 50 kHz and 500 kHz.

9. The soil moisture sensor of claim 1, wherein the drive signal frequency is between 100 kHz and 300 kHz.

10. The soil moisture sensor of claim 1, wherein the microcontroller comprises a pulse-width modulated signal generator that provides the drive signal to the series RLC circuit.

11. The soil moisture sensor of claim 1, wherein the series RLC circuit provides an input signal to the capacitive probe.

12. The soil moisture sensor of claim 1, wherein the output signal is dependent on the capacitance of the soil between the two electrodes.

13. The soil moisture sensor of claim 1, wherein the microcontroller comprises an analog-to-digital converter, configured to receive the output signal and convert the output signal to a proportional output voltage, and

wherein the microcontroller determines the capacitance value of the soil based on the proportional output voltage.

14. The soil moisture sensor of claim 1, wherein the capacitive probe, the series RLC circuit, and the microcontroller are located in a single unit.

15. The soil moisture sensor of claim 1, wherein the capacitive probe and the series RLC circuit are located in a portable unit and the microcontroller is located in a processing unit.

16. The soil moisture sensor of claim 15, wherein the portable unit and the processing unit are configured to communicate wirelessly.

17. The soil moisture sensor of claim 15, wherein the portable unit and the processing unit are configured to communicate via a wired connection.

18. A soil moisture sensor, comprising:

a capacitive probe comprising two electrodes configured to be inserted into soil and to provide an output signal dependent on the capacitance of the soil between the two electrodes;

a series RLC circuit electrically coupled to, and providing an input signal to the capacitive probe to induce the output signal;

a current-to-voltage converter configured to receive the output signal, and convert the output signal to a proportional output voltage; and

a microcontroller comprising

a pulse-width modulated signal generator configured to provide a drive signal having a predetermined drive signal frequency to the series RLC circuit, the predetermined drive signal frequency is selected with reference to a resonance curve of the series RLC circuit, and

an analog-to-digital converter configured to receive the proportional output voltage, and convert the proportional output voltage to a digital signal,

the microcontroller configured to determine a capacitance value of the soil based on the digital signal, and to determine the moisture content of the soil in view of the capacitance value of the soil and a dielectric constant of the soil.

19. The soil moisture sensor of claim 18, wherein the capacitive probe, the series RLC circuit, the microcontroller, and the current-to-voltage converter are located in a single unit.