Pulsing Third Brake Light Circuit


Posted on Feb 4, 2014

Any type of flashing light on the main brake lights is prohibited and illegal in most states of the U. S. A. I`m verifying for the same here in Canada. In the mean time, use this circuit at your own risk and be aware that the possibility exists to be stopped by law enforcement if you implement this circuit in your vehicle. Q1 is a PNP Silicon Audio Power Out/Medium Power Switch Transistor, 7A, with a TO-220 case. As long as you have


Pulsing Third Brake Light Circuit
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a transistor which is close it will work fine. The SCR is a 100vrm, 0. 8A, sensitive gate with a TO-92 case. Diodes D1, D2 and D3 are standard small signal diodes. Power diodes D4 and D5 are the 6A, 50prv types, cathode case. The 60vrm type will work as well. I used for IC1 & IC2 the LM555 type. P1 controls the `on` and pulse-duration, P2 controls the pulse-timing. When you first press the brakes, this circuit will turn on your 3rd brake light via the main brake lights. After about a second a series of short strobe pulses occur. The number of pulses range from approximately 1 to 10, depending on the setting of P1/P2 and when the brake pedal was applied last. After the pulses have been applied the third brake light assumes normal operation. The prototype was set for five flashes which seemed more than enough. Two days later I re-adjusted the trimmer potentiometers for 4 flashes-1/2 second pause-4 flashes. Looks pretty cool! The schematic consists of two 555 timer/oscillators in a dual timer configuration both setup in astable mode. When power is applied via the brake pedal, the brake light driver Q1 is switched on via the low-output pin 3 of IC2, and timer IC1 begins its timing cycle. With the output on pin 3 going high, inhibiting IC2`s pin 2 (trigger) via D2, charge current begins to move through R3, R4 and C2. When IC1`s output goes low, the inhibiting bias on pin 2 of IC2 is removed and IC2 begins to oscillate, pulsing...




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