Tail lights

Tail Lights #

One change I want to make to the car from the ‘stock’ setup is to put in sequential brake lights. The tail light lenses have three separate sections which works great for this. You can buy replacement kits which use LEDS and flash sequentially. So, naturally, I instead whipped out Kicad and started designing something up myself.

It has a Atmega 328p microcontroller, i.e. the chip you find in an Arduino nano. There are three banks of LEDS, one for each section in the lens. Each bank can be indepdendently PWM controlled by the 328p. So I’ll be able to adjust the brightness and turn each bank on and off independently.

The board has three digital inputs : lights, brake, and flash. I’ve not fully decided how these will be used. I think some experimentation will be required.

The ’lights’ input is a signal to indicate that the headlights are on. This would probably translate into the tail lights being normally off, but on at a low level when the headlights are on.

The ‘brake’ signal will be used to indicate that the brake pedal is being pressed. This will need to make the tail light brighter when the brake pedal is pressed.

The ‘flash’ input will be used to indicate that the turn signal or hazard lights are on. One challenge here is synchronisation. Say the left hand turn signal is on. I want the sequential tail light pattern to be in sync with the front turn signal light. Also, I want both sequential lights to stay in sync when the hazard lights are on. One way to accomplish this is to feed the flasher signal in on this input. The code can keep track of the on/off status of this signal and the interval between on and off.

Hardware and software are over in Github here.

One other design question that I’ve spent a lot of time thinking about is : where do I put the the charge ports? I want to implement both CCS and CHAdeMO, so I’m actually going to need two spots for these to live on the car. The original fuel filler is a very basic, single, small round opening. Far too small to mount a combo 2 port or a CHAdeMO port.

After a lot of head scratching, it dawned on me that I could turn each tail light into a door and put one port behind each tail light. Here’s a sketch of what I want it to look like.

The tail light doors will both hinge toward the middle of the car. The tail light lens has enough space to fit the PCB inside and put a flat piece of aluminium over the back. That way the tail light can still sit flush against the car when closed. I’ve got a couple of metal fuel door hinges from an old jaguar. I’ll put some sort of a rubber seal around the perimiter to try and keep water out of the charge ports.