R1______________6K8 1/4W Resistor
R2____________270K 1/4W Resistor
R3_____________22K 1/4W Resistor
C1____________220΅F 25V Electrolytic Capacitor
C2_____________10΅F 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
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 1000΅F 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.
Source: Electronics Lab