Rain Alarm Project

This project is straightforward and great for beginners. The core of the circuit is a pair of transistors configured as a Darlington pair, which provides high current amplification.

1. Prepare the Rain Sensor: On a small piece of PCB, create two non-connecting tracks that are very close to each other. These will act as your sensor probes. When water bridges the gap, it will complete the circuit.
2. Assemble the Circuit: Follow the schematic to connect the components on a breadboard or solder them to the PCB.
   • The base of the first transistor (Q1) is connected to one of the sensor probes through a 10kΩ resistor.
   • The emitter of Q1 is connected to the base of the second transistor (Q2).
   • The collector of Q1 is connected to the positive supply.
   • The emitter of Q2 is connected to ground.
   • The buzzer is connected between the collector of Q2 and the positive supply, with a 220Ω current-limiting resistor.
3. Power and Test: Connect the 9V battery. To test the circuit, put a drop of water across the sensor probes. The buzzer should sound immediately. When you dry the sensor, the buzzer should stop.