It really bugs me that the
Cayman
doesn't have auto
headlights
. Even my old
Chevy
Trailblazer from 2007 has auto
headlights
! It especially bugs me since all of the requisite equipment seem to be installed. Anyway, I'm still waiting on parts for my engine rebuild, and I've been running out of other stuff to do, so I decided to fix it.
The first thing I came across is the switches on
Amazon
, Ebay, and the like for Volkswagens. It looked pretty promising, since the switch and connector look the same. While I was researching, I found a forum post somewhere that someone had tried it on a 997 with no luck, but there wasn't any other information. I decided to buy one and see what its insides were up to. I also bought a used stock switch for the
Porsche
.
Once my switches arrived I opened them up to see how they compare. Turns out, even though they are exactly the same externally, the Volkswagen switch would slot in perfectly and plug right in, they are incompatible electrically. The Volkswagen uses a switched positive, and the Porsche uses a switched ground. So for anyone looking to try these, don't bother. It's a complete non-starter, the Porsche control module pulls the wires up to +12v when the switch is off, and turns the lights on when the switch shorts the wire to ground. The Volkswagen switch puts +12v to the wire to turn it on, but the Porsche PCM will just see this as the switch being off.
The MK6 switch PCB is on the left, the Porsche on the right. They look very similar, but don't be fooled.
That blew any chances of being able to make minor changes like re-pinning the connector or something to get it to work. But that was always a long shot. What I was really interested in was the little intermediary connector that plugged between the switch and the wiring harness and had the light sensor attached to it. If I could get into that connector, it would give me an opportunity to alter the signals from the switch to do my bidding. That little connector ended up being a best-case scenario. It was a little circuit that was doing exactly what I wanted to, albeit with +12v instead of ground.
Best yet, the connector was just a shell and the pins were standard .1" headers. So making my own board to fit in there would be easy. I drew one up and had it a week and a half or so later. For 9 bucks! I love the future.
Fits perfect
I designed it around components I already had, so I didn't have to order anything except the board itself. This one is my test setup with a socket for the microcontroller. This way I can take it off to reprogram it. Once the code is done, I'll solder one up permanently. It doesn't fit back into the connector shell with the socket, otherwise I'd just leave it.
After some bench testing to make sure it worked, I uploaded a simple blink program to flash the lights every few seconds to make sure everything worked and took a video.
A quick video of the test
Now I just need to get the light sensor hooked up and do some more testing.
Excellent write up, I admire your electronic capabilities.
Or you could by this:
Exclusive Porsche Automatic light switch System - PALS
Works fine, pricey, but does not require an electrical engineering degree lol.
I saw those, but I just couldn't get behind it. I get that this is a really niche product, and you're going to pay extra for it because of the low production numbers, but it felt like they were stuffing completely unnecessary features into it to make it more techy and justify a super high price. I just wanted my lights to turn on at night. I don't want GPS-enabled high-speed DRLs. At that point you're paying $600 to have a switch that just turns on your lights anytime you leave your neighborhood. I don't mean to bash their product, I'm sure it works great, it was just more than I thought was necessary.
Did some testing with a light sensor in place and everything is working like I expect it to. I think I'll solder up a permanent board and get everything installed and cleaned up and call it good for now. Once I get the engine rebuilt and put back in, I can do some real-world testing. The only thing I'm not 100% on is how much hysteresis there should be. Right now it's sitting at probably something close to 10% of the sensor's range, which based on bench testing should work, but we'll see.
Video of them working
The switch that I bought came with a light sensor, and I originally was going to use that. It's a photo diode, and worked pretty well, but getting the range dialed in was a little cumbersome. The resistance measured would range from just a few dozen ohms in bright sunlight, to several million ohms in the dark. That's quite a range. The transition from early dusk to after sunset would span several orders of magnitude. Obviously it works, because that's what the manufacturer used, and the switches seem to work fine, but I decided to try some other sensors to see what else might work. I looked around on eBay and bought a set of sensors from and Infinity G35. I chose those primarily because they often came as a set, and they were obviously two different sensors. One being a two pin, and the other three. This would give me more options to play with. Also they are cheap.
I couldn't really make heads or tails of the sensor on the right, but the one on the left turned out to be a photovoltaic sensor. Basically it's a tiny solar panel. Depending on how much light it's exposed to, it will output between 0 and a little over a half a volt with a pretty linear response. No wild changes happening during the transition from day to night. Perfect. I'm going to try to place it underneath the tweeter grill on top of the dash. It blocks some light, but testing looked good. If that doesn't work, I'll fit one of those tinted covers into the defroster trim and put it under that. I'll have to drill a hole in the trim, though, so I'll try to avoid that.
The black wire is going to be the sensor's home. I'll put some mounting tape or something to hold it down. The white wire is just the test setup.
The theory of operation is pretty simple. There's a 12 volt switched wire coming in from the harness that powers the board through a 5 volt step down regulator. The "home" wire from the switch is connected to one of the pins of the microcontroller. Whenever this pin is pulled to ground by the switch, the microcontroller starts measuring the signal from the sensor and compares that to a predetermined value. If the measured value stays lower for about two seconds, the lights turn on. They don't turn off again until a different, higher value is reached, so the lights don't turn on and off as you pass though shadows or something. The parking light and headlight wires are each connected to a transistor that pulls the signal to ground when triggered by the microcontroller. They're also directly connected to the switch so that you can still turn everything on manually. The fog lights bypass the microcontroller completely. Those will still need to be turned on manually if I want to use them. I also put a calibration routine in the code similar to what the Volkswagen switches have. If you flip the switch three times, it will measure the current light level and set that to your new turn on position.
Anyway, that's it. It seems to be working fine. Once I get the car back on the road and can test it out in the real-world. I'll come back and post a link to github with the code and board files in case anybody finds this in the future looking to see if those Volkswagen MK5 and MK6 auto headlight switches work in the Porsche and want to give it a whirl.
So - wonderful. Will there be a special edition Planet-9 kit available?
