Read External Button with Arduino Analog Pins

Projects General Guidance
11

blairallday:
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!

All voltages are relative to ground. If Arduino ground is not the same as the ground of what you would test then who knows what the either end sees?