This simple circuit that can be used to flash incandescent lamps up to 10W power rating.The circuit is ideal for making flashing beacons on automobiles and other applications like that.The circuit is nothing but  an astable multi vibrator based on Q1&Q2 ( BC557&BD139).The capacitor C1 is the main timing element which determines the flashing rate of the circuit.The switch S1 can be used as an ON/OFF switch.

Circuit diagram with Parts list.



  • Power the circuit from a 12 V battery or 12V DC power supply.
  • Assemble the circuit on a goood quality PCB or common board.
  • A 12 v , 10W incandescent lamp can be used as the load.
  • All capacitors must be rated 15V.


  1. Sir can you please send the design steps of this circuit.

  2. Anshumaan

    Sir, i used 220uF/10V for C1… My lamp is glowing continuously without blinking…So is it because i used 10V capacitor instead of 15V or something else? Pls Sir help me out

  3. Seetharaman

    Hi Frank C1 & C2 to 35 volts or greater and of course the bulb also to be 24 volts. the timing is not that much dependant on voltage.

  4. Frank Gardner

    The circuit you recommended works great. Thank you.
    If I may be permitted another question; What modifications other than the working voltage of C1 & C2 are required to use the above circuit on 24 volts?

    Thanks for your help.

  5. Frank Gardner

    How can I modify the above circuit to keep the off time at one second while increasing the on time to 4 seconds?
    I’m building a model lighthouse with an occulting light (on more than off). To be protypical the light needs to be on for 4 seconds and off for 1 second. I understand I can increase the value of C1, but won’t that increase the off time too?

    Thanks for your help.