The Prong soil moisture sensor for BBC microbit is a sensor board that can be directly mounted to a BBC micro:bit to monitor the moisture present in the soil. The two conductive tines are placed into the soil. Any water or moisture in the soil will conduct to give an analogue voltage that can be read by the BBC micro:bit.
Prong is powered from the 3V supply of the BBC micro:bit. Use either the USB or JST connector on the BBC micro:bit to power the circuit. Prong and the BBC micro:bit can also be powered from the Mi:Power board to create a compact stand-alone unit.
The board has been designed so that the BBC micro:bit can be bolted on using 3 x M3 nuts and 3 x M3 screws. Place the screws through the P1, 3V and GND holes of the PCB and BBC micro:bit, then use the M3 nuts to fasten together on the back of BBC micro:bit. Alternatively, croc-clips can be used to connect between the Prong and the BBC micro:bit.
If using the Mi:Power board then additionally connecting P0 means the BBC micro:bit can sound an alarm if the soil becomes too dry.
When fitted to the Prong moisture sensor, the micro:bit can be coded via any of the micro:bit editors, such as the Microsoft MakeCode editor.
To ensure that the Prong moisture sensor has a long and fulfilling life, it is better to write your code to perform a moisture check every so often rather than continuously. When the check is performed continuously it promotes rapid erosion of the electrodes.