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Discussion Starter · #1 ·
I have already added auto-on headlights to my Z3 (on with ignition, stays on 30 seconds after key is removed) by making my own headlight controller (the operation of the switch is the same). I am looking for opinions on my next electrical change.

I am going to make the headlights turn on for 30 seconds or a minute when the car is unlocked, like my last car (Acura TL). I am good with electronics so no problems there. I am looking for opinions on the following:

-How long should unlocking the car turn the headlights on for?
-Should the car trigger the headlights every time it is unlocked, or only if I hit unlock twice within a certain time-frame, like 30 seconds?

Since I'll handle signal-processing with a micro-controller, these two things are ultimately a matter of software. I just wanted to know what people thought would be most intuitive (unlock once vs. unlock twice to trigger headlights)...
 

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Discussion Starter · #3 · (Edited)
Summary: it's a custom circuit I built, not like I bought anything from the dealer...

Basically, I got a copy of the ETM (Electrical manual) for my model/year and learned what exactly the stock headlight switch did in each position. First, I tried using MOSFETs but they started smoking after a couple hours use, I never figured out why. Then I found some DPDT 12V relays that fit on a .1" grid, and built a circuit using the relays that did the same thing as the mechanical switch. I used DPDT not SPDT because the original switch connected more than 2 wires in 1 case (and they were all 3 separated otherwise).

So I just used some transistors to amplify an input "trigger" signal, to turn on the relays. That sums up the board that emulates the mechanical switch. I should note that I disconnected ALL wires from the switch, so right now the switch is used only to activate the relay board - that's how the stock switch retains stock function. The parking lights use the accessory line as their relay trigger, so they turn on at the accessory position.

I have a second board that controls the headlights' "trigger" signal. Basically, it senses two wires from the instrument cluster (12V2 and charging signal), so it can know when the engine is on. I use capacitors, resistors, and comparator chips so that the automatic function of the headlights will turn the headlights on only 2 seconds AFTER the engine starts (Xenons - I figured $2 in parts was worth it to protect them from under-voltage while starting). The comparators/capacitors etc can sense when the engine is off (no 12V2 signal), and those components have specific values for ~30 second delay before the relay signal is stopped.

I have since learned how to program micro-controllers, so if I were to do it again, I could do it more quickly, and make it more customizable. Right now I have variable resistors to control the on-delay and off-delay of the automatic headlights.

So, I plan to use micro-controllers to build a circuit that activates the headlight relay trigger upon double-unlocking (within a certain time-frame).
 
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