Two sensor types: Resistive sensors pass current between metal electrodes but corrode quickly. Capacitive sensors measure electrical capacitance — water has ~80x higher capacitance than air — with no corrosion and longer lifespan. GrowlyBox uses capacitive sensors.
Calibration: Map raw ADC values (0–4095) between dry soil and water immersion to get 0–100% readings. GrowlyBox firmware handles this automatically.
Placement: Insert at 1/3 soil depth (root zone middle). Too shallow gives misleading surface readings.