A Simple Automatic Plant Watering System without Microcontroller

This automatic plant watering system operates entirely on analog electronics without needing any programming or a microcontroller. At the heart of the circuit are BC547 NPN transistors arranged to act as electronic switches. The soil moisture sensor probes are placed directly into the potted plant's soil; when the soil is damp, electrical current can pass between the sensor probes, but as the soil dries out, its electrical resistance increases. This change in resistance is detected by the transistor network, which is adjusted using a 100k ohm potentiometer to set the exact dryness threshold. When the soil becomes dry enough, the transistors trigger, allowing power to flow into an RC timer circuit that utilizes a 680uF electrolytic capacitor and associated resistors (10k, 1k, and 500E) to govern the timing and delivery of voltage. Once triggered, this circuit activates the mini water pump, drawing power from a 5V USB power bank. The pump pushes water through the mini water tube to hydrate the plant. Once the water reaches the soil, the moisture level rises, the electrical resistance drops, and the transistor switch turns off the pump until the soil dries out again.