I saw another thread that was similar, but it didn't a definitive or clear answer on the matter.
I'll be brief. I want to install a Nexus 7 (2012) tablet in the dash of my car. I want it to be able to display video from a backup camera that I will mount in the trunk of the car. The camera will just be a Logitech webcam that I already have, but it uses USB. This is fine, because I'll just use a USB OTG Y cable with the tablet so that I can charge it and send the video data to it as well.
So, I want the camera to automatically display the video on the tablet when I go in reverse, but I need a way to detect this. After some research, I've concluded that I should splice in the power cable from the USB directly to the wire to the reverse lights, connect the ground cable to the car chassis, and then just send the data wires up front to the tablet.
My question is, is it okay if I just splice the power wire from the USB directly into the reverse lights? That way, when the reverse lights go on, the camera goes on, and the video app launches. My concern is that I could either be drawing too much power from the reverse lights, or the reverse lights provide too much power to the camera, which takes 500mA, per the USB 2.0 specification.
Also, if I were to do this, would I have to watch out whether I spliced the wire into a positive or negative wire for the reverse lights? Do those play some part in the switch that determines whether the lights are on or not?
Thanks for any input