SparkFun Micro:Bit Accessory Board
The SparkFun gator:soil micro:bit Accessory Board will allow you to measure the moisture level in soil. Best of all–it is part of SparkFun’s gator:bit series of alligator-clippable accessories, meaning you can easily interface it with the micro:bit or other microcontrollers.
The gator:soil consists of two probes and three pads (PWR, GND, and SIG). The 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). The value read on SIG is dependent on a few variable, including soil composition, contact on the probes, soil compaction, and other factors. In most cases, it will behoove you to calibrate your sensor reading for each soil sample and sensor. Once calibrated, for a fixed sensor, the primary variables to measuring conductivity in the soil will be the power input and moisture content of the soil.
We recommend powering the gator:soil with between 3.3V – 5V. Again, please note that the analog value returned will vary depending on what voltage is provided for the sensor. 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).