Soil Sensor. The 3.3k sets the Vref threshold value. Lowering resistance brings the threshold closer to Vcc. In this example roughly 300 ohms Measure the resistance of the soil in your watered plant at 1" depth, 1" spacing. Replace the 3.3k resistor with a trim pot. The probes go between Vcc and the non-inverting input of the op-amp. Use the trim pot to set the dry point. I am not an electrical engineer, just an enthusiastic amateur who loves electronics. Just my personal solution to a project I'm working on. Suggestions are welcome!
