WO2020041440A1

WO2020041440A1 - Capacitance-based soil moisture sensing

Info

Publication number: WO2020041440A1
Application number: PCT/US2019/047457
Authority: WO
Inventors: Sayjro Kossi NOUWAKPO
Original assignee: Board Of Regents Of The Nevada System Of Higher Education On Behalf Of The University Of Nevada Reno
Priority date: 2018-08-22
Filing date: 2019-08-21
Publication date: 2020-02-27

Abstract

Disclosed is an apparatus, such as a soil sensor, to collect a plurality of measurements, including a soil moisture measurement and a baseline measurement for comparison with the soil moisture measurement. Also disclosed is a method of sensing soil moisture in two or more different soil locations using two or more Internet of Things (IoT) soil moisture sensors.

Description

CAPACITANCE-BASED SOIL MOISTURE SENSING

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of U.S. Patent Application No. 62/721,510, filed on August 22, 2018, which is hereby incorporated by reference in its entirety.

FIELD

[0002] One or more implementations relate generally to capacitive-based soil moisture sensing, and some embodiments relate to an Internet of Things (IoT) soil moisture sensor.

BACKGROUND

[0003] Soil moisture is a soil property that controls many biophysical processes important to personal and industrial applications. In agriculture, information on soil moisture may be crucial to many aspects of production including: controlling crop growth, scheduling irrigation, planning field tillage operations, etc. In home and commercial gardening applications, accurate information on soil moisture is also important to automate water delivery based on plant requirements. In arid and semi- arid regions, soil moisture is an important metric to assess vegetation water stress, predict fire hazard, etc.

SUMMARY

[0004] Disclosed herein is an apparatus to collect a plurality of measurements, including a soil moisture measurement and a baseline measurement for comparison with the soil moisture measurement. In some embodiments, the apparatus includes a sealed enclosure; and a circuit board including a first section and a second section, wherein the first section is located within the sealed enclosure and the second section is located outside the sealed enclosure; the first section including circuitry including at least one integrated circuit; and the second section including: a first pair of electrodes located a first distance from an edge of the enclosure; and a second pair of electrodes located a second greater distance from the edge of the enclosure; the first pair of electrodes to remain exposed to a fluid while the second pair of electrodes flank the soil, the first pair of electrodes to provide a first analog signal to the at least one integrated circuit usable to obtain the soil moisture measurement and the second pair of electrodes to provide a second analog signal usable to obtain the baseline measurement.

[0005] Also disclosed is a method of sensing soil moisture in two or more different soil locations using two or more Internet of Things (IoT) soil moisture sensors. In some embodiments, a disclosed method includes inputting a time setting into a front-end application of a computing device coupled to the two or more IoT soil moisture sensors or using two or more user interfaces of the two or more Internet of Things (IoT) soil moisture sensors, respectively. If the time setting is input into the front-end application the method further comprises transmitting the time setting to each of the two or more IoT soil moisture sensors. The method also can include responsive to a current time matching the time setting, simultaneously collecting two or more soil moisture readings using the two or more IoT soil moisture sensors, respectively; and storing the two or more soil moisture readings in two or more memories of the two or more IoT soil moisture sensors, respectively, or in a data store wirelessly coupled to the two or more IoT soil moisture sensors.

[0006] The foregoing and other features of the disclosure will become more apparent from the following detailed description, which proceeds with reference to the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] FIG. 1A is a schematic illustrating an apparatus for collecting a plurality of measurements in accordance with exemplary embodiments disclosed herein.

[0008] FIG. IB is an illustration of a parallel plate capacitor showing the polarized dielectric allowing a charge Q to be stored on the parallel plates in accordance with an embodiment disclosed herein.

[0009] FIG. 2 is an illustration of the fringe capacitance principle used for the soil moisture sensor electrodes in accordance with an embodiment disclosed herein.

[0010] FIGS. 3A and 3B are schematics of the soil moisture sensor electrodes showing a top view (FIG. 3A) and a perspective view (FIG. 3B). [0011] FIG. 4 is a circuit diagram of a disclosed soil moisture sensor electronics showing a capacitance to a digital convertor, a temperature sensor, and a single-chip microcontroller and transceiver, SDA and SCL are serial data and clock lines of the communication bus.

[0012] FIG. 5 is a three-dimensional rendering of the soil moisture electronics board showing the capacitance to digital converter, the temperature sensor, and the single chip microcontroller-radio transceiver.

[0013] FIG. 6 is a top view of the soil moisture sensor boarding showing the dimensions of the electrodes and of the area supporting electronic components. Board thickness is l.6mm.

[0014] FIG. 7 is a three-dimensional rendering of the board inside the specifically designed enclosure. Transparency was set to 50% to aid visualization.

[0015] FIG. 8 is a digital image of a laboratory test of the IOT soil moisture sensor monitoring soil moisture changes in sandy soil.

[0016] FIG. 9 is a graph of volumetric soil moisture content Q_n as a function of soil capacitance for sandy soil in laboratory conditions.

DETAILED DESCRIPTION

[0017] Soil moisture is a property that may significantly vary over short distances and time spans. It may be beneficial on a farm field or a garden to monitor soil moisture simultaneously at multiple locations. In home applications, there may be a need to monitor soil moisture in multiple pots to provide individualized watering schedules based on water status in each pot. Some embodiments described herein provide a low- cost system to measure and monitor soil moisture simultaneously at multiple locations.

[0018] In the following detailed description, references are made to the accompanying drawings, which form a part of the description and in which are shown, by way of illustration, specific implementations. Although these disclosed implementations are described in sufficient detail to enable one skilled in the art to practice the implementations, it is to be understood that these examples are not limiting, such that other implementations may be used and changes may be made to the disclosed implementations without departing from their spirit and scope. For example, the blocks of the methods shown and described herein are not necessarily performed in the order indicated in some other implementations. Additionally, in some other implementations, the disclosed methods may include more or fewer blocks than are described. As another example, some blocks described herein as separate blocks may be combined in some other implementations. Conversely, what may be described herein as a single block may be implemented in multiple blocks in some other implementations. Additionally, the conjunction“or” is intended herein in the inclusive sense where appropriate unless otherwise indicated; that is, the phrase“A, B or C” is intended to include the possibilities of“A,”“B,”“C,”“A and B,”“B and C,”“A and C” and“A, B and C.”

[0019] Soil Sensor and Methods of Use

[0020] Disclosed herein are soil sensors and methods of use. Referring to FIG. 1A, apparatus 100, such as a soil sensor, to collect a plurality of measurements, including a soil moisture measurement and a baseline measurement for comparison with the soil moisture measurement is provided. In some embodiments, apparatus 100 includes a sealed enclosure 102; and a circuit board 104. In some embodiments, circuit board 104 includes a first section 106 and a second section 108, wherein first section 106 is located within sealed enclosure 102 and second section 108 is located outside sealed enclosure 102. In some embodiments, first section 106 includes circuitry, such as at least one integrated circuit. In some embodiments, the second section comprises a plural layer Printed Circuit Board (PCB).

[0021] In some embodiments, second section 108 includes a first pair of electrodes 110 located a first distance from an edge of enclosure 102; and a second pair of electrodes 112 located a second distance, such as at a greater distance, from an edge of the enclosure. In some embodiments, each pair of electrodes includes a coplanar electrode. In some embodiments, the length of the first pair of electrodes is different than the length of the second pair of electrodes. In some embodiments, the length of the first pair of electrodes and the second pair of electrodes is the same.

[0022] In some embodiments, the first pair of electrodes remain exposed to a fluid while the second pair of electrodes flank the soil. For example, the first pair of electrodes provide a first analog signal to the at least one integrated circuit usable to obtain the soil moisture measurement and the second pair of electrodes provide a second analog signal usable to obtain the baseline measurement. In some embodiments, the first analog signal represents fringing filed capacitance between the electrodes of the first pair. In some embodiments, the at least one integrated circuit comprises a switched capacitor circuit to transfer the first analog signal to an analog to digital converter (ADC). In some embodiments, the at least one integrated circuit is configured to apply an excitation voltage across the second pair of electrodes using a step waveform at 25 kHz. In some embodiments, the at least one integrated circuit is configured to provide active shield signals driven at a same frequency and voltage as a signal corresponding to a capacitance electrode of the second pair of electrodes.

[0023] In some embodiments, disclosed apparatus 100 includes a first shield 114 (see FIG. 3 A) surrounding a capacitance electrode of second pair of electrodes 112 and a second shield 116 (see FIG. 3 A) surrounding the other electrode of the second pair of electrodes 112. In some embodiments, a symmetrical and balanced shielding arrangement is coupled to the second pair of electrodes to constrain an electric field within the soil.

[0024] In some embodiments, the second section comprises a plural layer Printed Circuit Board (PCB), and the pair of second electrodes comprise metal embedded into both sides of the plural layer PCB.

[0025] In some embodiments, disclosed apparatus 100 is a soil sensor to collect a plurality of measurements, including soil moisture measurement and a baseline measurement for comparison with the soil moisture measurement. For example, the soil sensor includes a first section to insert into an enclosure, the first section including at least one integrated circuit; and a second section to protrude from the enclosure when the first section is inserted into the enclosure. In embodiments, the second section includes a first pair of electrodes located a first distance from an edge of the enclosure and a second pair of electrodes located a second distance, such as a greater distance, from the edge of the enclosure. In embodiments, the first pair of electrodes remain exposed to a fluid while the second pair of electrodes are located in the soil. For example, the first pair of electrodes provide a first analog signal to the at least one integrated circuit to obtain the soil moisture measurement and the second pair of electrodes provide a second analog signal to obtain the baseline measurement. [0026] In embodiments, a disclosed soil sensor includes a power connector, such as a power connector located on the first section, to couple to a power source, such as battery. In embodiments, the first and second sections of a disclosed soil sensor includes a single Printed Circuit Board (PCB). In embodiments of a disclosed soil sensor, the second section includes a first subsection and a second subsection. For example, the second subsection forms a plurality of ground spikes, wherein each electrode of the second pair of electrodes is located on a different one of the ground spikes. In some embodiments, the second section comprises ground spikes, wherein only one of the pairs of electrodes are located on the ground spikes.

[0027] Some embodiments may include IOT soil moisture sensors designed to be low cost to allow users to affordably deploy multiple sensors for various applications. The sensors may be low power so may require little maintenance from the user. Some embodiments may include a front-end application to control and/or monitor the soil moisture sensor network. This front-end application may be associated with short setup and configuration time from the user. Compensations for temperature changes and other environmental factors allows for high research-grade soil moisture measurement accuracy.

[0028] With improved knowledge on soil moisture content, users can significantly improve water use efficiency, effectively preventing fires, better plan farming operations, and collect high spatiotemporal data for research.

[0029] Some embodiments include wireless soil moisture sensors to allow for rapid deployment in the agricultural fields, for research purposes and for home and garden applications. In some embodiments, the sensors are used to detect water pooling at the soil surface to regulation irrigation rates. The sensors are designed to facilitate communication with other sensors. In some embodiments, the sensors are coupled to a remote device, such as a smartphone, a tablet, and/or some other computer, and may be capable of making independent decisions such as triggering irrigation. Furthermore, the sensors can be controlled remotely, including upgrading their firmware over the air.

[0030] The wireless sensor network in which these IOT soil moisture sensors operate may be scalable and may foster an extensible environment. In some embodiments, an IOT module may communicate and interface with agricultural hardware (such as an irrigation system) using IOT soil moisture data as input.

[0031] Some embodiments include sensors using Frequency Domain Reflectometry (FDR), which take advantage of the high dielectric constant of water (79) relative to air (~l) and mineral dry soil (~2.7).

[0032] Methods of sensing moisture are disclosed. In some embodiments, a method of sensing soil moisture includes a method of sensing soil in two or more different soil locations using two or more Internet of Things (IoT) soil moisture sensors. In embodiments, the method includes inputting a time setting into a front-end application of a computing device coupled to the two or more IoT soil moisture sensors or using two or more user interfaces of the two or more Internet of Things (IoT) soil moisture sensors, respectively. For example, if the time setting is input into the front-end application the method further comprises transmitting the time setting to each of the two or more IoT soil moisture sensors. The method also includes responsive to a current time matching the time setting, simultaneously collecting two or more soil moisture readings using the two or more IoT soil moisture sensors, respectively. In embodiments, the method includes storing the two or more soil moisture readings in two or more memories of the two or more IoT soil moisture sensors, respectively, or in a data store wirelessly coupled to the two or more IoT soil moisture sensors. In embodiments, the method utilizes a computing device coupled to the two or more IoT soil moisture sensors using a wired connection at programming time. For example, the time setting is transmitted using the wired connection, and wherein the two or more IoT soil moisture sensors are disconnected from the wired connection prior to a time of the collecting. In embodiments of the method, inputting the timing value into the front-end application further includes identifying a schedule using the front-end application.

[0033] In some embodiments, each IoT soil moisture sensor comprises three sections. For example, a IoT soil moisture sensor includes a first section forming a plurality of ground spikes; a second section comprising an enclosure and circuitry to receive the time setting; and a third section located between the first and second sections, the third section located outside the enclosure. The first section can include a first pair of electrodes to obtain a first capacitance measurement and the second section includes a second pair of electrodes to obtain a second capacitance measurement. In some embodiments, each soil moisture reading is based on a corresponding one of the first capacitance measurements and a corresponding one of the second capacitance measurements. In some examples, each IoT soil moisture sensor includes a reference capacitor to obtain a third capacitance measurement, and each soil moisture reading is further based on a corresponding one of the third capacitance measurements.

[0034] The specific details of the specific aspects of implementations disclosed herein can be combined in any suitable manner without departing from the spirit and scope of the disclosed implementations. However, other implementations may be directed to specific implementations relating to each individual aspect, or specific combinations of these individual aspects.

[0035] It should also be understood that some of the disclosed implementations can be embodied in the form of various types of hardware, software, firmware, or combinations thereof, including in the form of control logic, and using such hardware or software in a modular or integrated manner. Other ways or methods are possible using hardware and a combination of hardware and software. Additionally, any of the software components or functions described in this application can be implemented as software code to be executed by one or more processors using any suitable computer language such as, for example, Java, C++ or Perl using, for example, existing or object-oriented techniques. The software code can be stored as a computer- or processor-executable instructions or commands on a physical non-transitory computer-readable medium. Examples of suitable media include random access memory (RAM), read only memory (ROM), magnetic media such as a hard-drive or a floppy disk, or an optical medium such as a compact disk (CD) or DVD (digital versatile disk), flash memory, and the like, or any combination of such storage or transmission devices.

[0036] Computer-readable media encoded with the software/program code can be packaged with a compatible device or provided separately from other devices (for example, via Internet download). Any such computer-readable medium can reside on or within a single computing device or an entire computer system, and can be among other computer-readable media within a system or network. A computer system, or other computing device, can include a monitor, printer, or other suitable display for providing any of the results mentioned herein to a user. [0037] The following example is provided to illustrate particular features of certain embodiments. However, the particular features described below should not be construed as limitations on the scope of the disclosure, but rather as examples from which equivalents will be recognized by those of ordinary skill in the art.

EXAMPLE

[0038] Capacitance-based soil moisture sensing

[0039] A capacitor is a passive electric component composed of at least two metallic conductors often in the form of parallel plates separated by an insulating material called the dielectric. A capacitor is characterized by its ability to store potential energy in an electric field across the metal plates. When an electric potential difference is applied across the two plates, polarization within the dielectric causes some electric charges to be retained on the metal plates (FIG. 1B). FIG. 1B is an illustration of a parallel plate capacitor showing the polarized dielectric allowing a charge Q to be stored on the parallel plates.

[0040] The ability of the capacitor to store energy depends on the surface area of the parallel plates but is also a function of the polarizability of the dielectric. The dielectric constant e is used to characterize the ability of the insulating material to form a capacitor. The higher the dielectric constant of a material the greater its ability to store energy when used as insulating material in a capacitor.

[0041] Soil is made of three main phases: solids (minerals, organic fraction and sometimes ice), liquid (soil water and dissolved ions) and gas, mainly air. The dielectric constant of water is 80.4 at 20°C while for the soil solid and gaseous fractions, it is in the range of 1 to 5. This dramatic difference in dielectric constant between water and the other constituents of the soil makes capacitance an effective soil moisture measurement technique.

[0042] Capacitance-based soil moisture sensor with various electrode geometries are possible. Disclosed herein is a soil moisture sensor, which utilizes a fringing field capacitance in which the electric field is formed between two coplanar electrodes separated by a distance d and projected into the surrounding material (the soil) (FIG. 2). FIG. 2 provides an illustration of the fringe capacitance principle used for the soil moisture sensor electrodes in accordance with a disclosed embodiment.

[0043] Soil capacitance measurement electronic system

[0044] To measure the capacitance between the two electrodes of the moisture sensor, some embodiments use a Capacitance to Digital Converter Integrated Circuit (IC), such as FDC1004 from Texas Instrument. The Capacitance to Digital Converter IC can use a switched capacitor circuit to transfer charges from the soil electrodes to an Analog to Digital Coverter (ADC) circuit. In embodiments, the Capacitance to Digital Converter IC applies an excitation voltage across the soil electrodes using a step waveform at 25 kHz. In embodiments, to reduce the effect of parasitic capacitance on soil moisture measurement and improve noise immunity, the

Capacitance to Digital Converter IC provides active shields driven at the same frequency and voltage as the capacitance electrode. For example, one shield (Shield 1, 114) is driven in phase and at the same voltage as the capacitance electrode signal. Shield 1 is used to surround the capacitance electrode as well as its signal traces on the printed circuit board (pcb), limiting parasitic noise pick-up from the surrounding area (FIG. 3 A). A second shield (Shield 2, 116) is 180° out-of-phase with the capacitance signal which maintains a constant voltage with the capacitance electrode and is used for the return signal path (FIG. 3A). FIGS. 3A-3B show schematics of the soil moisture sensor electrodes showing a top view (3 A) and a perspective view (3B). A constant voltage between the capacitance electrode and Shield 2 allows a differential capacitance measurement to be made, thus avoiding stray capacitance to be formed on the ground path.

[0045] Further shielding can be achieved by underlaying the capacitance electrode with Shield 1 and the Shield 2 electrode with another Shield 2 copper layer (FIG. 3B). This symmetrical and balanced shielding arrangement allows the electric field to be constrained within the soil. In some embodiments, the electrodes are made of copper layers embedded into both sides of a 4-layer pcb.

[0046] In embodiments, the Capacitance to Digital Converter IC has a capacitance measurement range of ±15 pF. In embodiments, to constrain soil capacitance in a valid range, a predefined value capacitor (e.g., a !2pF value capacitor) is placed in series with the capacitance electrode, limiting measured capacitance to a maximum value of equal to the predefined value. FIG. 4 is a circuit diagram of a disclosed soil moisture sensor electronics showing the capacitance to a digital convertor, the temperature sensor, and a single-chip microcontroller and transceiver, SDA and SCL are serial data and clock lines of the communication bus.

[0047] In addition to the soil capacitance electrode, a shorter electrode with similar function as the soil electrode is connected to a second capacitance measurement pin of the Capacitance to Digital Converter IC. This second electrode is not to be in contact with the soil but left in the air to measure environmental baseline conditions (FIG. 4). In some embodiments, a reference capacitor, such as a l2pF reference capacitor, is also connected to a third capacitance measurement pin of the Capacitance to Digital Converter IC to track any potential drift or shift in capacitance measurement by the IC. In one embodiment, a temperature sensor (such as the TMP75 (Texas Instrument) temperature sensor) is placed on the board to track board temperature and used as observation data to correct for temperature-driven capacitance errors.

[0048] Data from the Capacitance to Digital Converter IC is transmitted via an I2C communication bus to a single-chip microcontroller/ radio transceiver IC (e.g., the ATMEGA256RFR2 (Microchip)). The single-chip microcontroller/ radio transceiver IC can be configured to periodically powers the Capacitance to Digital Converter IC and the temperature sensor through two of its input/output pins and request soil (C_son), air (Ca ) and reference (C_ref) capacitance data from the Capacitance to Digital Converter IC and temperature (T) from the temperature sensor. The sensor data is sent to a receiver via wireless communication and the single-chip microcontroller/ radio transceiver IC may power off the sensors and enters a sleep mode.

[0049] Wireless communication system

[0050] In some embodiments, a single-chip microcontroller/ radio transceiver IC has a 2.4GHz IEEE 802.15.4 compliant RF transceiver and allows programming multiple soil moisture sensors into a mesh network. A soil moisture probe is programmed as an end-device which implements a programmable sleep routine, and periodically sends data to the network coordinator or to another specifiable device. Data sent to a receiver are C_SOii, C_air, C_ref and the board temperature T. [0051] Board design and enclosure

[0052] FIG. 5 is a three-dimensional rendering of an exemplary soil moisture electronics board showing a capacitance to digital converter, the temperature sensor, and the single-chip microcontroller-radio transceiver. FIG. 6 is a top view of the soil moisture sensor boarding showing the dimensions of the electrodes and of the area supporting electronic components. In this example, board thickness is l.6mm. FIG. 7 is a three-dimensional rendering of the board inside the specifically designed enclosure. Transparency was set to 50% to aid visualization.

[0053] In some embodiments, the soil moisture sensor is built on a PCB shaped in a “T” with the electronics components mounted on the top wide section of the board while the soil and air electrodes extend at the bottom (FIG. 5). The short electrodes for ambient air capacitance measurement are 5 mm x 2 mm in dimension while soil capacitance measurement electrodes are 60 mm x 2 mm (FIG. 6). The top section of the board where electronic components are soldered measures 41 mm x 35 mm.

[0054] In one embodiment, a plastic enclosure is specifically designed to securely contain the electronic components of the board while allowing the electrodes to extend out of the enclosure (FIG. 7). The enclosure has a compartment on the back side for a power source, such as two AA batteries to power the device. The enclosure is designed to seal the electronics compartment from the outside.

[0055] In some embodiments, the short electrodes measure any fluid (e.g., a non solid, such as a liquid or a gas) above the soil surface. In one embodiment, the short electrodes may detect water ponding above the soil surface, which may be useful to control irrigation rate, etc.

[0056] Laboratory soil moisture measurement test

[0057] A volume of 400 mL of sandy soil material was added to a beaker and topped with 200 mL of water, yielding an initial volumetric moisture content of 50%. The saturated soil was set on an electronic scale to monitor changes in bulk mass as the water evaporates (FIG. 8). The developed IOT soil moisture sensor prototype was inserted in the soil to monitor changes in capacitance with soil moisture. For practical purposes, the sensor was kept out of its enclosure during this test to facilitate rapidly reprograming the single-chip microcontroller/ radio transceiver IC when needed. Capacitance and temperature data were sent wirelessly every 30 minutes to a data receiver connected to a computer which also controlled and interrogated the scale for soil weight once new probe data was available. FIG. 8 is a photo showing a laboratory test of the IOT soil moisture sensor monitoring soil moisture changes in sandy soil.

[0058] FIG. 9 is a graph of volumetric soil moisture content Q_n as a function of soil capacitance for sandy soil in laboratory conditions. Predicted soil moisture content (0_v_pred) using the piecewise displayed. Average experimental temperature was 21 degrees Celsius. FIG. 9 shows that changes in soil moisture content Q_n were captured by the soil moisture probe as increase in capacitance with Q_n. The relationship between Q_n and soil capacitance seems to be properly modeled by a piecewise function that breaks up around 2% volumetric soil moisture content. Between 0 and 2% volumetric moisture content, an incremental change in moisture content caused a rapid variation in soil capacitance. Beyond 2% volumetric moisture content, soil moisture steeply increased with soil capacitance. A coefficient of determination (R²) of 0.97 was calculated using the piecewise exponential function. Calibration curve are expected to vary depending on soil type.

[0059] While some implementations have been described herein, it should be understood that they have been presented by way of example only, and not limitation. Thus, the breadth and scope of the present application should not be limited by any of the implementations described herein, but should be defined only in accordance with the following and later- submitted claims and their equivalents.

Claims

CLAIMS What is claimed is:

1. An apparatus to collect a plurality of measurements, including a soil moisture measurement and a baseline measurement for comparison with the soil moisture measurement, the apparatus comprising:

a sealed enclosure; and

a circuit board including a first section and a second section, wherein the first section is located within the sealed enclosure and the second section is located outside the sealed enclosure;

the first section including circuitry including at least one integrated circuit; and

the second section including:

a first pair of electrodes located a first distance from an edge of the enclosure; and

a second pair of electrodes located a second greater distance from the edge of the enclosure;

the first pair of electrodes to remain exposed to a fluid while the second pair of electrodes flank the soil, the first pair of electrodes to provide a first analog signal to the at least one integrated circuit usable to obtain the soil moisture measurement and the second pair of electrodes to provide a second analog signal usable to obtain the baseline measurement.

2. The apparatus of claim 1, wherein each pair of electrodes comprises a coplanar electrode.

3. The apparatus of claim 1 or claim 2, wherein the first analog signal represents fringing filed capacitance between the electrodes of the first pair.

4. The apparatus of any one of claims 1-3, wherein a length of the first pair of electrodes is different than a length of the second pair of electrodes.

5. The apparatus of any one of claims 1-4, wherein the at least one integrated circuit comprises a switched capacitor circuit to transfer the first analog signal to an analog to digital converter (ADC).

6. The apparatus of any one of claims 1-5, wherein the at least one integrated circuit is configured to apply an excitation voltage across the second pair of electrodes using a step waveform at 25 kHz.

7. The apparatus of any one of claims 1-6, wherein the at least one integrated circuit is configured to provide active shield signals driven at a same frequency and voltage as a signal corresponding to a capacitance electrode of the second pair of electrodes.

8. The apparatus of any one of claims 1-7, further comprising a first shield surrounding a capacitance electrode of the second pair of electrodes and a second shield surrounding the other electrode of the second pair of electrodes.

9. The apparatus of any one of claims 1-8, further comprising a symmetrical and balanced shielding arrangement coupled to the second pair of electrodes to constrain an electric field within the soil.

10. The apparatus of any one claims 1-9, wherein the second section comprises a plural layer Printed Circuit Board (PCB), and wherein the pair of electrodes comprise metal embedded into both sides of the plural layer PCB.

11. A soil sensor to collect a plurality of measurements, including soil moisture measurement and a baseline measurement for comparison with the soil moisture measurement, the soil sensor comprising:

a first section to insert into an enclosure, the first section including at least one integrated circuit; and

a second section to protrude from the enclosure when the first section is inserted into the enclosure, the second section including:

a first pair of electrodes located a first distance from an edge of the enclosure; and a second pair of electrodes located a second greater distance from the edge of the enclosure;

the first pair of electrodes to remain exposed to a fluid while the second pair of electrodes are located in the soil, the first pair of electrodes to provide a first analog signal to the at least one integrated circuit to obtain the soil moisture measurement and the second pair of electrodes to provide a second analog signal to obtain the baseline measurement.

12. The soil sensor of claim 11, further comprising a power connector located on the first section, the power connector to couple to a battery.

13. The soil sensor of claim 11 or claim 12, wherein the first and second sections comprise a single Printed Circuit Board (PCB).

14. The soil sensor of any one of claims 11-13, wherein the second section comprises a first subsection and a second subsection, wherein the second subsection forms a plurality of ground spikes, wherein each electrode of the second pair of electrodes is located on a different one of the ground spikes.

15. The soil sensor of any one of claims 11-13, wherein the second section comprises ground spikes, wherein only one of the pairs of electrodes are located on the ground spikes.

16. A method of sensing soil moisture in two or more different soil locations using two or more Internet of Things (IoT) soil moisture sensors, respectively, the method comprising:

inputting a time setting into a front-end application of a computing device coupled to the two or more IoT soil moisture sensors or using two or more user interfaces of the two or more Internet of Things (IoT) soil moisture sensors, respectively;

wherein if the time setting is input into the front-end application the method further comprises transmitting the time setting to each of the two or more IoT soil moisture sensors; responsive to a current time matching the time setting, simultaneously collecting two or more soil moisture readings using the two or more IoT soil moisture sensors, respectively; and

storing the two or more soil moisture readings in two or more memories of the two or more IoT soil moisture sensors, respectively, or in a data store wirelessly coupled to the two or more IoT soil moisture sensors.

17. The method of claim 16, wherein the computing device is coupled to the two or more IoT soil moisture sensors using a wired connection at programming time, wherein the time setting is transmitted using the wired connection, and wherein the two or more IoT soil moisture sensors are disconnected from the wired connection prior to a time of the collecting.

18. The method of claim 16 or claim 17, wherein inputting the timing value into the front-end application further comprises identifying a schedule using the front-end application.

19. The method of any one of claims 16-18, wherein each IoT soil moisture sensor comprises three sections, including:

a first section forming a plurality of ground spikes;

a second section comprising an enclosure and circuitry to receive the time setting; and

a third section located between the first and second sections, the third section located outside the enclosure;

wherein the first section includes a first pair of electrodes to obtain a first capacitance measurement and the second section includes a second pair of electrodes to obtain a second capacitance measurement, wherein each soil moisture reading is based on a corresponding one of the first capacitance measurements and a corresponding one of the second capacitance measurements.

20. The method of claim 19, wherein each IoT soil moisture sensor comprises a reference capacitor to obtain a third capacitance measurement, and wherein each soil moisture reading is further based on a corresponding one of the third capacitance measurements.