Read External Button with Arduino Analog Pins

Projects General Guidance
6

Here's a link to a gdrive with some images of the PCB.
https://drive.google.com/open?id=17m56AQSdA9G-cEwOW_kqIYQVuLzyllcP

Here are the measurements I took with a multimeter:

  • Red (+) to Black (-): 0.40V

  • Yellow (+) to Black (-): -1.60V

  • Green (+) to Black (-): 0.10V

  • Green (+) to Yellow (-): 1.8V [Button Not Pressed]

  • Green (+) to Yellow (-): 0V [Button Pressed]

When I try to measure these lines to the Arduino ground, the reading fluctuates in the mV range.

When I attach an analog pin to one of these lines, it confuses the PCB (lights go off, button doesn't work).

Since the yellow to black voltage is negative, I think the green and yellow lines form a loop that's independent from the red and black lines.

Thanks for the help!