We apologize for this issue, we had a mistake with the labeling on the board! If you reverse the GND, and the 5V on the Alt-power the power will work and the board will be recognized by Planet-CNC.
Once again we apologize for this issue!
Thanks - glad it is an easy fix! You guys should update the docs - perhaps on the item description for the future confused.
We updated the product page to reflect this error. Many thanks!
FYI - to anyone who reads this - reversing the polarity on the 5v alt power will indeed damage the board, though not immediately.
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I decided to connect 5v directly to my usb breakout board, but when I plug the usb cable in, the planetcnc app does not recognize it and the green status light does not come on. I've confirmed that it is getting exactly 5v, and the jumper is removed.