This project is very useful for cinema, factory, building, and hospital.  This project gives information about resumption for power supply through alarm sound.  By listening the alarm you can stop the generator starter at the time of power supply failure.  If you are busy with the work you are not aware that when electricity is restored.  The running of generator will cost the price of diesel.




This project is based on popular IC NE555.  It is used in monostable mode.  When electricity supply is restored it triggers the IC.  The pin no. 4 & 8 of the ICs are positive pins.  Whereas pin no. 1 is the negative pin.  The pin no. 3 is the output pin.  When IC is triggered the output signal is available at pin no. 3 which is given to the transistor Q1 [BEL187] through resistance R1 [330E].  The output voltage at the collector energized the relay.  Due to this the pole of the relay gets connected with the normally open contact, which is connected high sound buzzer are alarm circuit of AC230V.  This buzzer or alram gets AC 230V supply through relay.  You get the information about AC230V electric supply through sound alarm and stop your running generator.


A stepdown transformor 12V-0-12V / 50mAmp is used for 12V DC supply for this project.  Through diode D2, D3 [IN4007] and condenser C4 [1000mfd/40v], the supply is rectified and filtered to make pure 12V DC supply.  This supply is used to operate the project.  The period of alarm is set by the variable control VR1 [1ME] and condenser C3 [100mfd/40v].  From pin no. 2 of the IC a condenser C2 [1mfd/40v] is grounded.  The alarm will stop when period set for the alarm is over.  The main attraction of this project is that after the information about alarm is received it automatically gets OFF.  There is no need to get up and to stop the alarm.



  1. Use IC base for the IC.
  2. Take care that there is no shorting on PCB while soldering the components.
  3. First of all, check all the components so that all components are OK.
  4. Take care of cathode and anode terminals of diode while soldering on PCB.
  5. Use good quality relay.
  6. Take care while solder the positive and negative terminal of condenser.