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Brake Light Flasher

Posted by bates70 on October 30, 2010

I saw the F1 race and it was raining, I was very interested in the rear brake lights of the cars are race. Cool out!. when the brake lights with F1 style can be applied in my car. The things that really gets other driver attention when i stepped on the brakes. But government regulations prohibit the obtaining flashing brake lights because they endanger other drivers.
The solution is a circuit that will flash the brake lights for a short time when I press and hold brake. After several flashes, the light would stay on continuously, until I released the brakes. The short burst of flashes certainly gets the other drivers attention. Short duration flashes solve the problem of annoying people behind you. I get an electronic scheme on radio shack. With this electronic scheme of government regulatory issues resolved and the purpose of getting attention from other drivers behind you still achieved.

Automotive Brake Light Flasher

Parts List:
IC1 = CD4093UBE, CMOS (4093B)
Q1 = 2N2222
Q2 = TIP117

R1,R6 = 50K trimpot
R2,R5,R7,R9 = 10K
R3 = 100K
R4 = 47K
R8 = 2K7

C1 = 33uF, 25V
C2 = 3.3uF, 25V

PCB flashing brake lights

Circuit Description :
The schematic shows the circuit for the brake light control. It consists of four sections that are un-powered when the brakes are off. When the brakes
are applied, +12VDC (13.8V) is connected to the circuit (point A). The circuit then controls the voltage to the brake light. When the brakes are
released, the +12VDC is removed, and the circuit and brake light are no longer powered.
The first section provides a pulse delay to allow the brake light to pulse for only a short period of time. R1, R2, R3, C1, and IC1a form a
half-monostable inverter. When the brakes are applied, C1 is charged through R1 and R2. When the voltage across R3 reaches the trigger level of C1
the output at pin 3 goes from +12 volts to zero (point B). Trimpot R1 allows the pulse delay time to be adjusted.
Resistor R3 provides a discharge path for capacitor C1 after the power to the circuit is removed (via the brake switch wire). What this means is that
there is no delay for the brake light to come on in between brakes, the flasher works as it should all the time. You can press the brake pedal as fast as
you can and as often as you can, the flasher will work fine every time
The second section provides the pulse rate for the brake light. R4, R5, R6, C2, IC1c, and IC1d, form a free-running astable oscillator. When the brakes
are applied, the circuit is powered and starts oscillation. The pulse rate is determined by the time constant of resistors R5 + R6 and capacitor C2.
Trimmer R6 allows the pulse rate to be adjusted to your personal liking. The pulse rate output is taken from pin 11 of IC1d (point C).
The third section combines the pulse rate signal and the pulse delay signal. IC1b ‘NANDS’ the two signals to produce a series of pulses followed by a
constant high level (point D). This will form the On-Off sequence of the brake light.
The forth section is the driver that controls the output to the brake light bulb. Resistors R7, R8, R9, and transistor Q1 form an inverting amplifier. This
drives the pull-up power transistor, Q2. The brake light will light as Q2’s collector is pulled to +12VDC (point E). The return path to ground is the
chassis or frame. The negative of the battery is connected here also.

Installation :
Installation all depends on your bike’s wiring system but most of them are all the same. Look for the wire coming from your handbrake and footbrake,
mostly combined into a single wire underneath your seat. Cut this wire and mount the flasher unit in between these two wires. One end that goes to
your brake switches is the +12V and goes to point ‘A’. The other end connects to point ‘E’. One wire more to connect and that’s the negative or ground
wire, that one connects simply to your bike’s chassis. In short, cut your brakelight wire and connect this circuit in between.

This design works much better and more reliable then the 555 timer design of the same, elsewhere listed on the circuits page. The 4093 design does
away with the delay. There is no delay for the brake light to come on between quick brake pedal presses and the circuit overall works fantastic and
very reliable.
For the TIP117 (Q2) I used a replacement type made by NTE Electronics, the NTE262. Works great. But a TIP125 or TIP127 will also work.
For the capacitors I used Tantalum types because I had them in stock, but they are not as reliable as standard electrolytic caps.


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