Hi- I've got a situation where I'm trying to read three analog pins of the Uno, and all three pins are following each other regardless of what the actual signals are doing. For example- if I connect one jumper wire to any one of the pins of the UNO, and leave it floating, all three oscillate wildly. If I ground that wire, all stablize at 0. Same if I peg it with a pull up, all three go high, even though I'm only changing one. I'm using short wires (5cm), and this sort of set up is working fine on another Uno board (I'm trying to recreate a working project on another breadboard so I can do some improvements without taking the original project offline). I expect the oscillation if a pin is floating, but even with all grounded, taking one high takes all high. Pins are adjacent, A1, A2 and A3. Pins A4 and A5 are running as SDA/SCL for RTC and are behaving fine, but I don't know if there is anything shared between the ADC pins. I can post my code if needed, but since this seems to be a physical phenomenon, I thought maybe it wasn't needed?
UPDATE- I was cheating and trying to use 5v and Gnd to represent the output of an LDR with analog read (so I didn't have to mess around with LDRs on my breadboard since I just want to see what happens with my sketch when I cross a threshold). For the sake of troubleshooting, I fully rebuilt the other working project including LDRs as a voltage divider- and now it works as expected. I'm still stumped as to why this would have a different outcome? Only thing I can think of is that I was basically "slamming" the ADC high and low, but should that matter? Maybe ADC doesn't like full 1023 values? Is there capacitive coupling between the pins, which is why they were all copying each other?