Two-wire Lamp Flasher

Ideal to operate 3 to 24V DC existing on-circuit lamps

LED operation is also possible

Lamp Flasher


R1______________6K8  1/4W Resistor
R2____________270K   1/4W Resistor
R3_____________22K   1/4W Resistor

C1____________220µF   25V Electrolytic Capacitor
C2_____________10µF   25V Electrolytic Capacitor

D1___________1N4002  100V 1A Diode

Q1____________BC557   45V 100mA PNP Transistor
Q2____________BD139   80V 1.5A NPN Transistor

LP1___________Existing filament Lamp: any type in the range 3-24V 10W max.

SW1___________Existing On-Off switch

B1____________Existing V DC source: any type in the range 3-24V
                       suited to the lamp adopted

Device purpose:

This circuit has been designed to provide that continuous light lamps already wired into a circuit, become flashing. Simply insert the circuit between existing lamp and negative supply.
Especially suited for car or panel pilot lights, this device can drive lamps up to 10W.


  • Break lamp(s) to negative supply connection(s), then insert the circuit between existing lamp(s) connection(s) and negative supply (respecting polarities!).
  • C1 value can be varied from 100 to 1000µF or higher, in order to change flashing frequency.
  • Although rather oversized, this circuit can also drive any LED, providing a suitable resistor is fitted in series with the light emitting device.
  • The resistor should be in the range 47R to 2K2, depending on supply voltage.

Title: Two-wire Lamp Flasher
electronic circuit
Published on: 2005-02-03
Reads: 767
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