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