This circuit was 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.
Circuit diagram:
Led or Lamp Flasher Circuit Diagram
Parts:
R1 = 6.8K
R2 = 270K
R3 = 220K
D1 = 1N4002
C1 = 220uF-25V
C2 = 10uF-25V
Q1 = BC557
Q2 = BD139
B1 = Any type in the range 3-24V
B1 = Suited to the lamp adopted
LP1 = Filament Lamp 10W-3V to 24V
SW1 = On-Off Switch
Notes:
- Break lamp to negative supply connection, and then insert the circuit between existing lamp connection 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 lie in the 47R to 2K2 range, depending on supply voltage.
Source: Red Free Circuit Design