2. p-n-p transistor (2N 557)

3. Two rain sensors ( aluminum tube of diameter 5 mm and length 6-7 cms)

4. One LED and one resistance

5. One capacitor (0.2 microfarad)

6. 3 resistors (220 kW, 100 kW, 15 kW)

7. Battery 

8. Switch

9. Wires

10. Plastic plate

Working Principle:

Two conductors (rain sensors) are placed closed together but they are not allowed to touch each other. There remains a gap between them. When water falls on the circuit, it allows the current to flow through it which sends the current to make your alarm glow or beep, either way you like. You can make an alarm which glows or beeps when it rains!

Construction:

Important thing is to join the components correctly for which I am sharing the circuit diagram in next section which will help you to make connections easily and moreover the current produced by the circuit is very minute which can only make LED to glow or could make buzzer to produce sound. Current less than 40 volts can’t be sensed by human body. It’s not dangerous at all.

Your water alarm can be activated with the help of a single water drop too!

Aluminum tubes (rain sensors) are fixed on a plastic plate with a small distance between them and water acts as a medium of connection between them and with the competition of circuit, your LED will glow.

Circuit diagram and its significance:

Circuit diagram plays a very important role. If your circuit diagram is correct, then definitely your rain alarm will work, only need is to join the components correctly and components should be in condition to work. Ruined parts could create problems.

Join circuit as shown below. At the place of LED, you can join buzzer. Buzzer will produce sound and LED will glow when it rains. Rest of the circuit and components will remain same.

I’ve always liked to join circuits. It’s quite interesting to see a circuit on paper and then further joining it with your own hands. It will produce very less current which can other lighten up LED and noting more than it. But join correct terminals and use wires which can only take lesser current. 

It’s fun to join your own circuit and make your own alarm. Especially, high school students can make it easily. It would be better if you consult your science teacher before joining it. 

Enjoy and have fun with your own Rain Alarm!