I have a simple photoresistor displaying values on a serial monitor every second so I can establish a value that I want to use to have it activate a relay.
It has worked fine for a few weeks, with bright sunlight values about 1000, total dark is 0. I soldered only the headers on a protoshield, and stacked it on the Arduino. I have nothing else on the protoshield and I am still using jumper wires to a breadboard, which I have not changed.
Why would the photoresistor values drop to approximately 40 (from 900's) when I stack the second board on the Arduino?