Project-1: Rain Alarm & Water Tank Alarm

Today we are going to make an essential but very simple alarm system. This alarm can be used with any fluid that has at least a very low level of electric conductivity. Water is a polar substance so we can use this alarm system as a rain alarm or we can use it as a water tank alarm.

In many third world countries a lot of electricity is wasted for the overflow of water in the main tank so it can come into handy as a water tank alarm.

The whole circuit is divided into two main sections.
a. The electronic circuitry
b. The Sensor

We are going to discuss it one by one.

a. The electronic circuitry
The main circuit consists the following parts (including their value):
1. fixed resistor (47k + 1.5k )
2. ceramic capacitor (0.01 micro farad)
3. n-p-n transistor (D-400)
4. p-n-p transistor (2SB54)
5. loud speaker (8 ohm)
6. battery (9 volt)

b. The Sensor
The sensor can be made on a pcb (printed circuit board). Even you can make it on a breadboard or acrolyc plastic board. Make a google search to know how to make a pcb. There are two points in the sensor named M & N which are going to be connected on the main circuit board point M & N.

To know about the symbols please visit this page.

How does it work?
To use it as a rain alarm the sensor should be put in such a place where direct rain drop can drop onto it and when the M & N point gap is filled with a water drop a small electronic signal is generated and this signal is the amplified by the transistors and fed into the speaker as an audio alarm. To lowering the sound level of the alarm we can replace the 47k fixed resistor with 220k/330k fixed resistor.

In case of water tank alarm the sensor should be put into the higher level of the tank connected with a long ware to the circuit inside the home. The whole circuit requires a 9 volt dc power supply.