I was wondering if it was a bad idea to ground a separate voltage source through the ground on the arduino. I have a 24VAC source that im running through a separate circuit, but I need somewhere to tie the ground up. I thought I could just connect it but I wanted to make sure before I blow anything u haha. If this is a bad idea what would be an alternative?
Please show a circuit of what you are doing.
Depends how much current is flowing through that ground link.
If the Arduino supply circuit and the 24v AC supply circuit are separate, then joining grounds is probably not a problem. A ground link is usually needed for small control currents (transistor base current, sensors, etc.). Opto links can be used if joining grounds is not possible or dangerous. If you're not sure, post a diagram of your circuit. Leo..
I assume this is for your sprinkler valve project. http://forum.arduino.cc/index.php?topic=321929.0 Did you already get a 24v AC supply, and a relay board. If no galvanic isolation is needed, a TRIAC can also be used to switch AC. A triac can be driven straight from an Arduino pin (with 220ohm gate resistor).
Did you already try the solenoid on DC. http://www.instructables.com/id/A-watering-controller-that-can-be-home-networked/step9/DC-vs-AC-Solenoids/ Then a mosfet switch can be used. Leo..
The source is rated at 750 mA (AC). And yes the two sources are separate, i just need to share a ground and that’s all the two circuits would have in common with each other.
A warning with irrigation solenoid wiring. You are correctly using AC for control but make sure there is NO DC leakage.
I say this from experience! An engineer designed a commercial reticulation system that used triacs for switching. However there was a very small DC leakage in his design. It ended up with a large park needing the wires replaced.
It's not required that you connect the AC source to Gnd. What you must connect, to Gnd or some other reference voltage, is the power driver (relay, FET, triac...) input, that requires a defined voltage between two pins (signal and reference). Connecting the AC source to the driver may establish a connection to the Arduino Gnd, with possible (ground loop) problems when not wired properly.
Using a relay will prevent such bad effects, isolating the driving logic from the power circuit.