Custom Turn Signal Retrofit - Part 1

After an interesting winter with a mix of snow and temps on either side of freezing, water made its way into some of the light housings of my car... namely the front turn signals. The bulb sockets corroded and rusted to the bulbs, making things messy and more or less unusable. Everything is all just kinda shorted together. Now I can order new housings for around $70, but why not mod the ones I have? I can't ruin them any further. Let's throw in an ultra-bright LED.

Now this actually presents an interesting set of challenges. You can't simply throw an LED and resistor in there and watch it work (well, you actually kinda could, but that's no fun). But here are a few items to consider:

- The vehicle voltage can vary, especially if the engine is running or not. The battery will read a pretty steady 12V, but may sag under the load of you headlights an other accessories. Running, the system voltage is often around 14V. If using a current limiting resistor, you'll see some different intensities depending the actual voltage present. This is actually already an issue with the standard bulbs, but one that can be addressed.

- The current bulb is a typical 1157. It has two filaments; one to act as a running light when the headlights are turned on, and the other for the actual signaling. I'm only adding one LED element for both purposes.

- The 1157 has a low output filament which produces about 38 lumens at around 8W and a high output filament that'll do 402 lumens at 27W (see table). My particular LED is capable of outputting 900 lumens. But I'm not what exact current is gonna be needed to produce the right amount of brightness for either function. I'd like to have a little adjustment.

- The original bulb uses 27W for the turn signal. The signal timing relies on the 2 point something amps being drawn to toggle a bi-metallic switch.

- I want this project to be fun.

As always, seems like a good opportunity to use a microcontroller. What can't they do? With a really basic micro and a bit of circuitry we should be able to make something that operates over a varied input range, performs two output functions, and has adjustable brightness. And some sort of short circuit protection... cause that's part of the original problem.... water.

Until next time....