Two-wire Lamp Flasher

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 :

Two-wire Lamp Flasher Circuit Diagram

Parts:

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

Notes:

• 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 lie in the 47R to 2K2 range, depending on supply voltage.

Source : redcircuits