Well, I continue to work on this and now have a beta unit in my car on a long term test. It is pretty rough around the edges and has one major(ish) issue that I am working to resolve, but its a good starting point to work from.
So what I have now looks a bit like this:
(click to enlarge)
Its still a very simple design that uses as few components as I can, but as a result it has some issues:
- As the the LEDs are quite hungry (50Ma each) the ATMega328 & the voltage regulator has to work hard to feed them.
- The above point causes a small delay in start-up of the unit of around 200-300ms.
This delay is a problem as the unit is powered by the feed to the brake light, when the brake is pressed, so in essence it adds a small delay between the stop/tail lights of the car illuminating and the high level brake light. Long term this is unacceptable, but for now its a work in progress so I can live with it.
The first generation PCB was designed to fit into the dust cover of the brake light, but after I attached the ribbon cables for the led's it didn't fit so is now wedged under the parcel shelf for now. This gives me easy access form the boot to change the unit as I progress the design to remove the delay and make it instant. Here is the mock-up of the PCB using matrix board (left to right we have the finished design, the component layer, the jumper cable layer on the front, and the soldered join layer on the back):
And the finished article looked like this:
In the end I decided to opt to hot glue the LED's into the reflector and wire them back via a ribbon cable to allow me more flexibility on changing the circuits easily:
Long term I intend to make a unit that can replace the original light bar, so the LEDs will be mounted direct to a PCB that will be installed into the light bar in some way, or easily attached to the back of the reflector housing, not sure which yet.
I am working on a number of new designs at the minute that remove the delay and am getting some help from a true expert in the field of automotive electronics who actually designed stuff that is used in the Mclaren MP4-12C.
The current V3 unit that is in the car looks like this when operated:
You can download all of the project files (sketch, layout & schematic) from the downloads section.
Watch this space for V4 of the unit.