Ok, so I have now managed to read the values I want and successfully been able to use them but I have now encountered another problem.
I have 2 built in LED's (technically 3) in the pc chassi wich are controlled by a PCB and a button. I then try to read the signal from an extra cable (R,G,B,12V) for additional RGB LED's or strips using a voltage divider connected to the PSU GND and the Arduino GND. But when I connect my Arduino to read the values, one of the case LED's light becomes more and more "distorted".
To make it more clear, the case LED's glows magenta, and I have nothing connected to the cable. I then connect one Arduino pin to the cable and ONE of the case LED's becomes slightly less magenta. I connect the second Arduino pin and the LED becomes even less magenta. Connecting the third pin makes the LED go more or less white.
Note that this only happens for one of the built in LED's, the other keeps its colour and is not affected at all. But if I disconnect the affected LED the other previously unaffected LED gets the same distorted color, and returns to normal when the other LED is connected again which gets distorted.
The things I have tried to resolve my issue:
- Increasing and reducing the resistor values of my voltage divider - no effect
- Checked the current in the GND wire - didn't notice anything weird, no high currents