In this circuit, the infrared emitter IRED1 is modulated by connecting its anode (A) to ~38kHz signal yielded by D9 of the Arduino Uno (TP1) while its cathode (K) to a ~1kHz signal available at D8 of ...

Analog Link. It is also possible to read the amount of moisture present in the soil (for judging whether the soil is wet or dry) by linking the analog output (AO) of the module, to one analog input ...