HK4 Hardwire Kit in a Tesla & Parking Mode & Raspberry Pi

[Okkie]

When connecting the HK4 to a car, the RED cable goes to some permanent 12V source. The BLACK cable goes to any ground and the YELLOW cable goes to some source that switches on when the car is running. It is called ACC (or sometimes IGN) because it normally activates when the key is turned into the ACC position.

But what if the car does not have such a power source? In a Tesla model 3/Y (and maybe others) there is no fuse box. There is no easy to find power source that only carries 12V when the car is in driving mode. There are ways to get a permanent 12V that actually carries 16V on newer models, but they are not permanent and neither represent driving mode. In fact, they are powered whenever the car is not in deep sleep mode. When the car is charging, or when the car is in one of the A/C modes or when the car is in Sentry Mode, the 16V is always powered. Which is okay, since the need for the Viofo to run nicely matches the need for Sentry Mode to run. So far so good.

But I would like to activate Parking Mode when not driving. For some reason my WM1 "knows" that when the HK4 is connected, it can obey it's ACC-signal and ignore the GPS and Motion settings. But since I had to connect the yellow and red lines together to the 16V source, the Viofo never enters Parking Mode! Only when I disconnect the yellow line it immediately enters Parking Mode and stays there until I connect it again.

Now I'm thinking of building something around a Rapsberry Pi to drive that ACC input. It can piggyback on another project I'm also contemplating, so this might sound more overengineerd than it is. If I can determine the driving mode from my code in that Pi, I could trigger the ACC line to the HK4 and switch between Parking and Driving mode. But, now I've introduced what I know about the HK4, here's my question:

What do we know about the ACC input? Of course connecting some random 12V to it, will toggle the Parking Mode flag. But what kind of input is it? Can I directly feed one of the IO-lines to it? Probably not. Or is it some high impedance open collector mumble something? Then the 5V from the Pi might trigger it. Is there some datasheet describing it? Anyone else already did some digging I could not find?

 

[DAP]

My solution to this problem was to not use a hardwire kit at all. I have my cameras powered by the cigarette lighter outlet, and set to motion detect mode with parking mode off. This means when the car is parked with sentry mode on, the dash cams are also on, but only recording when something moves in front of the camera. The draw back is that sometimes the cameras stop recording when I am sitting at a stop light for a long time, but otherwise they work fine.

 

[Okkie]

I did not like automatic detection for the reasons you mention. I had it running from the cigarette lighter until I got time to install the HK4. But then I got surprised by the HK4 to disabling automatic detection and depending solely on the state of the ACC connection. My personal preference is to hardwire the dashcam though, and now I got the wire all the way behind the dashboard and the console to the third party OBD2 connector behind the seats that I used to provide +16V and Ground. This frees up the cigarette connector for other purposes and it looks much neater. Switching back to the original cable means I have to redo all that hard work to get all the panels open and wires pulled through.

So now I got this weird idea to scan the can bus on the OBD2 connector for signals that indicate a 'driving' state to switch the ACC line.

Another neat idea would be to get permanent 16V directly from the low volgate battery and ACC from the backlight of the screen, but then I have to go places where I don't have the courage to go...

 

[DAP]

As for cosmetics, I tapped into the back of the cigarette lighter outlet, so all my wires are hidden.
One of the problems with the Tesla is that the cigarette lighter outlet or USB ports are the ONLY places that Tesla expects unpredictable current draw. Any place else you tap in might trigger some error code when the car sees more than the expected current draw. Teslas do not have any fuses (besides the pyro fuse on the high voltage battery), everything is monitored electronically, and electronically switched. I do think that Tesla should have provided some spare power taps for aftermarket accessories.
I think you are going to run into more trouble than it is worth trying to decode the OBD2 signals, but if you enjoy a challenge, go for it.

 

[Okkie]

As for cosmetics, I tapped into the back of the cigarette lighter outlet, so all my wires are hidden.

Nice. I had access to that point too when opening up the console, but would have to cut into the wire. Since I already had that OBD2 conenctor, I could tap into that without irreversably altering anything.

One of the problems with the Tesla is that the cigarette lighter outlet or USB ports are the ONLY places that Tesla expects unpredictable current draw. Any place else you tap in might trigger some error code when the car sees more than the expected current draw. Teslas do not have any fuses (besides the pyro fuse on the high voltage battery), everything is monitored electronically, and electronically switched.

Good point, but according to the electric schematics I found somewhere, the cigarette lighter is powered from the same electronic fuse. The OBD2 connector is a Y connector between the connectors that hooks up the console to the rest of the car, if you understand what I'm trying to express here. In fact my dashcam runs from the same wire as yours, only a bit further upstream.

I do think that Tesla should have provided some spare power taps for aftermarket accessories.

Agreed. An "ACC" wire that powers up whenever the car is ready to drive would be great too.

I think you are going to run into more trouble than it is worth trying to decode the OBD2 signals, but if you enjoy a challenge, go for it.

For that I need to go back to the original question:

Does anybody know the specifics of the ACC input? How can I best drive it from anything beyond some good old relay?