I posted before but it seems the post was eaten somehow... So I'm posting again.
What I'm attempting to do - and it seems good on paper - is to tap into the touch screen in an Eonon head unit. The unit itself is great but the software is TERRIBLE. The Eonon people really need to sell a head unit with VGA in and USB out for the touch screen. When I'm done, I'll be able to still use all the original functions (backup cam, DVD with secondary monitor output, etc) and toggle to the aux input, then flip a switch and toggle to the piggybacked USB touch screen interface and use the computer.
So what I have done is take the faceplate apart and I soldered leads to the 4 pin digitizer cable. I've isolated the onboard touch screen controller (it seems there is a SoC that runs the "OS" inside the faceplate itself!) and have found what line is the +5v power. I intend to cut that trace and wire in a toggle switch to alternate power to the onboard touch chip and then to the USB interface that I bought from Ebay. My theory is that I will be able to use the Eonon functions and when I want to use the CarPC, I can change to the aux input on the head unit, flip the switch, and go to town.
Has anyone tried this before? Am I in uncharted waters? I think this should work but I'm not 100% on if I can have the touch screen connected to both interfaces (but one on at a time) and not change the resistance values that the embedded OS is expecting from the onboard chip. Guess I'll know in a week or so when the interface comes.
I know everyone's going to say "just get a liliput" but I already own the head unit, it is already amped, has a radio and dvd player, etc... that I don't have to duplicate inside the PC.