Police flasher with transistors

The entire connection is realized by means of three astable flip-flops. The middle flip-flop controls the transistors T1 and T2. It controls on which side the connected LED will be lit. The other two flip-flops control transistors T3 and T10, which control the number of flashes on the LED. Only passive components are used – 10 transistors, the connection is not complicated and therefore recommended for beginners.

Circuit design:


The connection is powered by the car’s on-board voltage or any source with a 12V DC output. A maximum load of 500mA can be connected to the output. BC337 transistors are sufficient for two LED panels with 48 LEDs.

Placement plan:


Printed circuit board:


Placement plan and PCB are at 1:1 300 dpi (How to print a PCB design can be found in the post How to print PCB design). Real size PCB is 73,0 x 31,4 mm.

Part list:
C1, C2, C5, C610uF/16V electrolytic
C3, C4100uF/16V electrolytic
R1, R6, R11, R161k
R2, R5, R7, R10, R12, R154k7
R3, R4, R8, R9, R13, R1433k
T1, T2BC327
T3, T10BC337
K1-K3screw terminal for PSB, RM=5mm, 2 pin

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