[astine]

FYI, It's ok to output at 3v3 volts to a 5v device if the device will still work, but don't read input from a 5v device or you might damage your Pi; the pins are wired directly to the Broadcom chip with no resistance.

[StavrosK]

Oh, indeed, thank you. I don't have anything to read at the moment, but I'll keep it in mind!