He doesn't mention it directly but if you look at the pix you can see a resistor inline and he kinda tangentially mentions limiting current to prevent disaster.

He doesn't mention it directly but if you look at the pix you can see a resistor inline and he kinda tangentially mentions limiting current to prevent disaster. I suggest throwing a LED in series too, when it lights up you've found yourself a ground pin. Look for fun with pull-up resistors, sometimes you'll need to pull up and down. I2C with pullups on both pins unless you have active termination comes to mind. So throw another pull up in parallel with the existing hardware, nothing happens, hmm... Sometimes you're gonna want to pull down thru a resistor too.