fpp;

DO NOT use an LED to check for USB power!

Typical (classic) LED's run on about 2 volts. 5 volts at sufficient current can cause them to explode, possibly sending bits of plastic out at high velocities. 5 volts from a battery powered device will probably just damage the LED, but it is possible that a PC, or even a hub with a large filter capacitor could make the LED fail violently.

An LED and the proper resistor is safe, but is not "proper tools".

I would not connect anything I built/hacked/whatever to my 770 without testing with a good and trusted DVM.

That is correct.
;