Rain Alarm Circuit using Transistors

Rain Alarm Circuit

A rain alarm sensor circuit is very beneficial device for alerting when rainfall. The following circuit diagram is Rain alarm circuit. The diagram shows a water detection circuit. It consists of two NPN transistors. When there is no  rain fall on sensor its resistance decrease and due to that small current flow from + to base.

When current pass through sensor to base T1 open and current flow from emitter to collector. Cotter of T1 connected with the base of T2 as base of T2 sink current from the emitter of T2 it open and buzzer ring.

water on sensor , transistor T1 is blocked and T2 also blocked because base is empty of both transistors. When the sensor resistance drops below 4MOhm, T1 conducts together with T2 which turns on the piezo buzzer. The alarm is active for about 15-20 seconds until capacitor C1 is discharged. After the alarm, wait about 5 minutes for the capacitor to be charged and ready to use again.
The sensor can be ordinary 2 wires on the surface where water may appear. A better option would be to solder the wires to a PCB board arranged as shown roughly on the diagram.

Component Used

  1. Speaker pizo
  2. Transistor BC547
  3. Transistor BC547
  4. Resistor 10k
  5. Capacitor 0.01 mfd
  6. 3v to 6v battery
  7. Sensor  (Two built on a plastic board to detect water of rain)

Rain Alarm Circuit 2


Rain Alarm circuit
Working of the Circuit:
This rain alarm circuit consists of two transistor the 1st one is NPN (BC547 or BC548) and senond 1 is PNP bc 556/bc557 or bc 558). Working of the circuit is simple the transistor BC547B is working as a switch in this circuit when the water droplets fall on the sensor the transistor will become switched on and the 9V will start passing through the transistor which will activate the Buzzer.

Component Used

  1. Speaker pizo
  2. Transistor BC547
  3. Transistor BC558
  4. Resistor 10k
  5. Resistor 330k
  6. Capacitor 0.01 mfd
  7. 3v to 6v battery
  8. Sensor  (Two built on a plastic board to detect water of rain)

2 thoughts on “Rain Alarm Circuit using Transistors

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