Hi, I am hoping for some help on how to progress with my project..
I am trying to make a data logger for my floor heater control box. I have three thermostats that each activate a 24V valve depending on temperature. I want to latch on to these 24V signals, voltage divide them down to 5V and connect them to three input pins on the Arduino so I can do digitalReads.
I use three separate voltage dividers so the pin voltages don't depend on how many valves are switched on. The dividers have common ground on the arduino. I tried connecting the control box negative terminals to arduino gnd too. But I couldn't make it work, and was very confused why.
Until I discovered that the heating control box creates its 24v voltage difference, not by pulling up its positive terminal like I am used to, but by pulling down the negative. This means that the positive terminals act as common ground for the control box, while the negative terminals are generally not at the same voltage.
This messes up my approach because the arduino needs a common negative ground to get distinct positive signal inputs. My first thought was that I need to flip the signal polarity, but I don't know how to do that or if I am missing some easy solution.
I will make a schematic if the text doesn't make sense, so please let me know if it is necessary. Thanks for your help in advance!