This relay module has the option of monitoring light, soil moisture, or temperature with the included sensors. Only one sensor can be used at a time and the sensor type being used can be set with a jumper. A threshold can be set and the relay will turn on when the sensed value falls below the programmed value. This is very useful in a system that may water a garden or yard when soil moisture falls below a pre-determined level.
Two modes can be used. The relay can either be on until the desired threshold is reached or it can be on once the threshold is reached.
Using the thermometer this module could be used to turn on a fan or AC unit to keep a room at below a desired temperature. The inverse could be done with a heater. The included relay can control a 20A AC load.