Hello again, Arduino forums! Today I'm using a set of phototransistors (five of them) on a breadboard to sense light. I've set up the circuits correctly, but I'm using a common ground for all five phototransistors - that is messing up the readings a lot. I have determined this by changing my circuit setup on another breadboard, singling out the fact that the common ground is the real problem here. I tried using the digital pins as grounds (set to INPUT, write pin HIGH) with no luck.
There are only three ground pins on the Arduino I'm using. How do I effectively "ground" all five phototransistors so I can get accurate readings from them? There is probably an easy answer to this but I'm new to the world of circuitry.