Custom Microprocessor Controlled Lighting System
I've designed a small microprocessor board to control the signal lights, brake lights (with center brake light), emergency flashers, park lights and a security feature that will tie in with the car alarm. All the lights on my car will be super bright LEDs so the current draw will be very small versus normal tungsten lights.
Here's the completed microprocessor controller - tried, tested and true..
Inputs Description Right Turn Signal +12V signal from turn signal lever in right position Left Turn Signal +12V Signal from turn signal lever in left position Emergency Flasher +12V Signal from emergency flasher switch Park lights +12V Signal from light switch Park position Security signal +12V signal from car alarm indicating alarm on Brake light signal +12V signal from brake pedal switch Outputs Left front signal light Left front sidemarker light Left rear sidemarker light Left rear brake light Trunk center brake light Right rear brake light Right rear sidemarker light Right front sidemarker light Right front signal light
Some of the features that I put in are:
- Sidemarker lights alternatively flash with front/rear signal/brake lights
- Park lights are pulse width modulated for 33% duty cycle at 2kHz which means that you only run one wire to each light.
- Emergency flasher alternatively flash sidemarker lights with front/rear lights and then un-intentionally will cycle so that left and right side lights will be in synch and then go the exact opposite of each other. Looks like the alternating headlights of a police car. In cycles back and forth between normal and police car style. Don't know why but it looks cool.
- The security mode cycles the lights one at a time around the car starting at the left front signal light then down the left side, across the back, up the right side to the front and over again.
- If the car alarm goes off, the emergency flasher overrides the security feature - looks like all hell breaks loose!
- Center brake light works independantly of left/right brake lights
Techno Babble
I used a 68HC705 microprocessor running at 2 MHz internal clock cycle. Programmed in assembler and used about 256 bytes of code. Used two interrupts: real time clock to generate 1 Hz signal for flashing lights and a timer overflow for generating a 2 kHz pwm output for the park light feature.
The hardware ended up to be 4 digital logic chips and 1 microprocessor. 10 identical output drivers are used with one as a spare. The outputs can provide +12V at 4A each though I won't need anything near that. Input to the microprocessor are protected with zener diodes and a resistive voltage divider.
A 7805 (TO-220 package) provides +5V for the microprocessor and digital logic. Once I'm completely happy with the board, I'll coat it with a protective coat of clear conformal coating.