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SparkFun gator:soil Hookup Guide

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Contributors: santaimpersonator, Englandsaurus
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Hardware Overview

The gator:soil consists of two probes and three pads (PWR, GND, and SIG).

Note: For more in-depth information on the circuitry, check out the blog post for the circuit that this sensor is based off.
Contacts Description
PWR INPUT: Power to the sensor (3.3V - 5V).
SIG OUTPUT: Analog voltage representing the conductivity between the probes.
GND REFERENCE: Ground reference (0V).
Probes Used to sample soil moisture content for sensor.

Power

We recommend powering the gator:soil with between 3.3V - 5V. Please note that the analog value returned will vary depending on what voltage is provided for the sensor.

Power Connections
Power connection pads.

For use with the gator:bit (v2) and micro:bit, you should provide 3.3V through the PWR and GND pads. We recommend not powering the sensor constantly to reduce corrosion of the probes; this can be controlled through one of the digital pins of the gator:bit (v2).

Caution: One commonly known issue with soil moisture senors is their short lifespan due to corrosion of the electrodes from electrolysis. To combat this, we've had the PCB coated in Gold Finishing (Electroless Nickel Immersion Gold), which has a high decomposition potential. However, the life span of the sensor is limited. Applying a higher input voltage, taking frequent readings, and/or leaving the sensor on for extended periods of time will decrease the lifespan. For example, a simple way to extend the lifespan of your sensor is to only power it when you take a reading.

Output Signal

The two probes are used to measure the conductivity of the soil. SIG provides an analog voltage out that can be attached to an ADC pad on the gator:bit (v2).

Analog Connection
Analog signal connection pad.

The value read on SIG is dependent several variables such as soil composition, contact on the probes, soil compaction, amongst other factors. For example, if you have a high alkaline content in your soil, it will be more conducive and give you a high baseline reading. In most cases, you will probably need to calibrate your sensor reading for each soil sample and sensor. Once calibrated, for a fixed sensor, the primary variables to the measure conductivity in the soil will be the power input and moisture content of the soil.

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