Ok, I've got a weird one for you guys.

Hey Stephen,

I got the code configured and loaded, but i am having issues. I can't seem to get anything to report back from the Arduino. If I leave the Arduino board on USB 5V and common ground the boards i still get nothing. If I run the Arduino off on the 5 V from my power supply (with common grounds) weirdness breaks out.

RepRap will report 0 degrees C but the Z MAX LED comes on. it only goes off if i unplug the arduino breakout board all together, or unplug the USB Cable.

With the break out board unplugged and the usb cable still inserted neither boards report voltage on the ZMAX pin (its only when they are mated).

Ugh. If i touch the gnd on the usb to the gnd on the board three lights come up, and when i plug the cable back in two opto switches blink (opposite of each other. one is the ZMAX).

This has got to be a ground loop issue.

Any ideas?

Are you removing the link on the Arduino board completely?

If you are running the Arduino on the 5V form the power supply you must totally remove the power selector link ie so its not linked in the USB direction and not linked in Arduino on board regulator direction. If you don't you will get all kinds of weird effects as the two different 5v supplies will react to each other casing strange currents flowing between them based on different noise levels on the supplies and of course any voltage difference they might/will have.

I just point the link out from the board only connected at one end on the central pin.

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