Rain alarm circuit

Transistor:

A transistor is used to amplify the signal or electrical power. It is a semiconductor with three terminals. When a voltage is applied to the terminal of transistor it works as a gate to the other external circuit loop. All embedded circuit includes these transistors as packed inbuilt. We are going to use BC547 transistor in circuit we will also use this transistor in may basic electonics circuits like IR sensor, LDR sensor, Light sensor, Shadow sensor etc.

Circuit diagram:

Breadboard Diagram

Working:

In above circuit we have used two transistors but it can be done with one transistor also in case of water and if we want moisture thing to be sensed we can use more than two transistors. A transistor has 3 pins collector base and emitter. When any signal voltage is given to the base or we can say base voltage gets high the charge on the collector drops toward emitter side. Here the transistor connects the ground pin of the buzzer and led to the ground voltage terminal when signal is given to the base. Here signal to the second transistor is coming from the emitter side of first transistor. The drop terminals are two pins or we can use open wire one of which is connected to the base of transistor and other with main +ve voltage when a drop of water touches this two pins together the main voltage connects with base of first transistor a resistor of 1k is connected to avoid voltage increment damage. So this action makes first transistor drops the voltage to the base of second transistor and second transistor then connects the Buzzer and LED to the ground which makes the light glow and buzzer beep.

Component required:

• Two BC547 Transistor (NPN)
• Resistors

R1 = 1K

       R2 = 1K E

       R3 =1K

• Buzzer
• On/off switch S1
• LED
• 9v batterywith cap