Cameras on my hummer

[Bayleaf36ff]

I drive a hummer with a oretty big lift, and the blind spots are terrible. I about smashed a motorcycle today because he was riding right beside my back tire, and I never saw him.

I want to install small cameras on my side mirrors, and when i hit my turn signal, I want it to show that side's camera on my radios screen.

I jave all of the rca cables and radio controls figured out. I need help with the switching.

The turn signal switch is essentially a giant set of resistors. There is a purple wire coming out of it with a constant 13v on it when the vehicle is on. When you hit the left turn signal, it drops to 3.5v. When you hit the right, it drops to 7.5v. This purple wire goes to the computer, and tue computer powers the light bulbs based on what voltage is being input.

So, when i hit the left turn signal, the purple wire drops to 3.5v. I need to send 12v to the left camera, and 12v to the radio to tell it to display the camera. I have the camera cables and all figured out, that isnt the issue. How do I build a circuit that can detect the voltage difference, and if 3.5v is coming in it sends power to the left, if 7.5v it sends power to the right, and if 13v it does nothing? Are there relays that would only close at exactly 3-4v and 7-8v?

My other thought was to open the turn signal switch and try to solder wires straight to the contacts before the resistors, but my fear is that Ill change the load on the circuit and change the voltage down the wire, causing my turn signals to not work.

Thanks for your help!
Jeremy

 

[Harald Kapp]

You could use a window comparator to detect when the voltage from the turn switch is within a certain voltage range. You need to make that a range, not a specific voltage, to account for variations in the power supply.
A suitable chip is e.g. the LTC1042. Or you can build one from 2 operational amplifiers (dual opamp) as shown here.
In any case you'll need 2 window comparators.
Set #1 to e.g. 2 V <= active <= 5 V, this one will be active on a left turn.
Set #2 to e.g. 6 V <= active <= 9 V, this one will be active on a right turn.

These comparator circuits will not be able to power your camera directly. You will need to use the output from the comparator to drive e.g. a relay which in turn supplies power to the camera.