I'm contemplating building a simple HUD for a '97 A3 to show the speed and engine revs by reflecting digital displays off the inside of the windscreen. While I'm happy about putting together the electronics and displays, I need to pull the speed and rev signals from somewhere. I was hoping somebody might know something about the following or be able to suggest a helpful website:

a) What format are the signals in when they leave their respective sensors (road speed/engine speed)? I'm hoping it's just a voltage proportional to the speed/revs.

b) Where would be the best place to pick up the signals? Obviously they must arrive at the instrument panel in order to drive the speedo/rev counter, but it's difficult to work out which cables are involved. I've got the Haynes wiring diagrams but they don't really help in this case.

I'd be grateful for any information or advice.

Thanks.

 

Hello, i was thinking of the DIY but found there is a device already on market....price is ok....display is limited though....only speed
I have seen it on conrad electronics (www.conrad.nl)...i live in Netherlands
From what i can tell most newer cars should have a port at the back of the display that you can just plugin to....I think this might be similar or a secondary VAG-com.....
Maybe instead of rebuilding the whole system it might be better or easier....to get the off the shelf version which i think is limited to what it displays and modifie this to display more....incorporate menus settings etc...i.e software and maybe a bit of hardware...
I also couldnt figure out if it was possible to plugin to my A3 (1997) so left left the idea......i would also be interested in this....would appreciate anything you find out......
If you want more info on off the shelf device or maybe some help.....let me know....
Good luck