@KiraKiraSoul said in Expansion Board 3.0 Vin (3.5-5.5V) pin: In other words, is the input voltage regulated in any way on the expansion board? No. It's the same signal, just differently labeled. When connected to USB, you should see 5V at that pin coming from USB. Otherwise you can supply a xxPy device at that pin with input voltages from 3.5-5.5 V.

According to the data sheet, the maximum input voltage for a digital input is 3.3V. The maximum input voltage for the analog Pins vary according to the attenuator setting and should not higher than the analog range. I remeber to have seen a spec about that, but cannot find it again. If you connect a switch with a longish wire, please add protection circuitry, at least an RC lowpass (e.g. 100k in series/1nF to GND) element as close as possible to the input to suppress spikes. Please not