LED Brake Light

The high-level brake light on my car was deep and obstructed my rear view. So I made a replacement from four LED strips. Here's the comparison.

Here's the original lamp.

I ordered four LED strips and stuck them to a piece of aluminium, which I'd drilled and bent to the correct shape.

The result is a bright lamp, which doesn't obstruct my view.

I wanted to add a circuit to make the LEDs dim after a few seconds because it's quite annoying for the driver behind when you are stationary with the brakes on. (Here in Greece it's common to do that because, unlike the UK, there is no red-amber phase for the traffic lights. They switch from red to green and, if you aren't already moving, you get honked!)

I took a circuit, which I'd originally used some decades ago to make a windscreen wiper delay unit, and modified it to create a one-shot monostable. The LED strips light brightly for 10 seconds (about 500 mA) then dim, as the PNP transistor switches off and current flows only through the 150 Ohm resistor. (About 50 mA.)

First I built the circuit for testing on a simple breadboard. Amazingly, it worked at the first try!

The PNP transistor is one that I had lying around. It's rated at 3 Amps but any PNP transistor rated at 1 Amp would suffice. Any general purpose NPN transistor can be used instead of the 2N3904.

Here's the final circuit built on perforated copper stripboard.

Mounted in the car.

You can see a short video of the delay/dimmer unit on test on the bench, here:
https://youtu.be/GOGiJ0Uyc4Q

A note about these LED strips. As far as I can determine, 12.0 volts is the absolute maximum voltage for reliability. Since a car produces at least 13.6 volts, the life of the LEDs will be short if they are on permanently because they will overheat. (I know this from practical experience.) It's necessary to use a DC voltage regulator or do as I have done and add a timer so that they can't remain on for very long. That way they should last a few years.

Note, too, that I affixed the strips to an aluminium bracket, which helps to take away some heat.

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