The output frequency 555 is given by the following equation. Please read the article Astable Multivibrator using 555 Timer for more explanation about it.

WorkingĪs explained above, the 555 timer is wired as an astable multivibrator. R2 is the emitter resistor and R1 is the base resistor of the transistor Q1. BC547 transistor is wired as a switch whose collector is directly connected to the VCC. Capacitor C2 is connected to the 5 th pin to avoid high frequency noises. Resistors R3, R4 and the capacitor C1 will set the time period of oscillations produced by 555. A buzzer is connected to the 3 ed pin (output) of 555 timer, so it will produce sound depending on the output of 555. As you can see above 8 th pin (VCC) of 555 is connected to positive of the supply and 1 st pin (GND) is connected to the negative. The heart of this circuit is a 555 Timer wired as an astable multivibrator. Components RequiredĬircuit Diagram Rain Alarm using 555 Timer – Circuit Diagram 555 Timer Pinout This circuit make use the principle that normal water can conduct some amount of electricity ( PURE water is not a good conductor of electricity but water seen in nature is not pure). This circuit can be used as rain sensor, water overflow sensor or as a water level sensor. As you might already know, a 555 Timer can be easily wired as Astable, Monostable or Bistable multivibrator. Here is a simple and interesting hobby circuit that can be made using the popular 555 timer IC.

555 timer pinout download