Simplest lamp flasher circuit.

john June 4, 2009 19 Comments

This is a very simple lamp flasher circuit that uses only three components (a capacitor, relay and one resistor) other than the lamp. The working of the circuit is very straight forward. When the power is switched ON the capacitor C1 charges through the resistor. When the voltage across the capacitor is sufficient, the relay switches ON and the lamp connected via the normally open contact of the relay glows. The relay remains energized until the capacitor discharges and then the lamp extinguishes. The charging and discharging cycle of the capacitor gives a flashing effect to the lamp.

Circuit diagram with Parts list.



  • The relay L1 can be a 12V SPDT relay.
  • The lamp L2can be a 12V, 5W lamp.
  • The frequency of flashing can be varied by changing the value of C1 and R1.

  • aishwarya
    January 22, 2014

    please,I want more application regarding to simpler lamp flasher circuit?Also what is time required for charging and discharging of capacitor?

  • Hasan
    January 11, 2014

    This circuit is modified by someone only by changing its relay using 5V relay, and he said it can improve the timing stability. Check it out here

  • Adam Burnhams
    January 23, 2013

    Very helpful simply circuit. Does the bulb glow slightly when the capacitor is charging? With your set up of a 220 ohm resistor and 2200 uF capacitor how long is the bulb off for and on for in each cycle? Thanks,

  • seetharaman
    November 6, 2011

    Hi Swap use the same circuit with 9 volt relay

  • swap
    November 5, 2011

    i need an flaher ckt which works with 9v.

  • hamed
    October 18, 2011

    you dont make c1 because coil is 1n4001 diod

  • hamed
    October 18, 2011

    hi i like to web site m.r Praveen Thomas thank you

  • Edgardo Diolola
    October 16, 2011

    Thank you seetharaman, can you tell me how to calculate the frequency in order to know the flashing rate of the circuit, say; varying the values of R1 and C1

  • seetharaman
    October 15, 2011

    Hi Elgardo the circuit is meant for 48 volt bulb only. or use two 24 volt bubls in series. if you have only 12 volt bulb use four in series.

  • Edgardo Diolola
    October 15, 2011

    ok thanks a lot, but what about the lamp, the 12 volts, 5 watts lamp will surely get busted when 48 volts is fed through relay contacts, can I insert another 1k, 5 watts resistor between 48 volts and the 12 volts lamp?

  • hamed
    October 13, 2011

    i am from iran your website very good

  • seetharaman
    October 11, 2011

    Hi Edgardo replace the relay with 48 volt relay and increase the R1 from 220ohms to 1k 5 watt. use 63 volt or 70 volt capacitor instead 25volts.

  • Edgardo Diolola
    October 8, 2011

    Hi, how can we have a circuit for this simple flasher to work on 48 volts DC power supply as in battery operated forklifts? I wished to build one basing on this idea.

  • ashok
    December 4, 2009

    hi i need flasher circuit which is working in 24 volt dc

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