First of all I've like to mention that I'm by no means an electrical engineer. I'll try to explain what I mean with the title.
I have installed a headunit which has an option for a reverse camera. The headunit has a trigger wire which takes anything from 0 to 12 V.
I know an alternator makes it be 14.4 V approximately but for easyness sake we'll keep it at 12 V. If the trigger Wire notices a signal, it triggers the backup camera display in the headunit and a 12 V+ signal on a different wire.
The way the camera is now connected is as follows. I tapped in to the switched positive lead from the reverse lights and connected it to the trigger wire. The switched 12 V+ from the headunit, I connected to the camera positive lead. The camera negative lead goes to the reverse light negative lead. The issue with this is that BMW and possibly other brands as well, use a lower voltage test signal to see if the reverse lights still work (so they can show a notification on the dashboard) this triggers the trigger wire on the headunit and that will show the reverse camera.
This is not desired behaviour since I only want it to turn in when it gets more than let's say 12 V. I have a bunch of PNP and NPN transistors laying around as well as resistors and capacitors.
I'd like to avoid using a microprocessor to identify the signal. Is it possible to create the logic I'm after with just basic electronical components and how would I do this?