I just bought one of these to read the raw serial output from my Arduino. It seems pretty straight forward to connect, just TX, RX, and Grnd?
Why does it also have a VCC pin and a 3.3v pin? I'm assuming it has an alternate use outside of just reading serial output?
Yes the Vcc is just the +5vdc voltage power provided by the USB connection from the PC. You would make no connection to this pin unless you wished to power your external circuit from this device. The 3.3vdc is also optional power provided by an internal 3.3 volt voltage regulator inside the device chip, but caution to not draw too much current from that pin as it's pretty limited in capacity, maybe 50ma max? The Vcc is also limited but I can't tell you if it's 100ma or 500ma max as that is a function of USB connection and software negotiation performed between the device and the PC. Note that this device lacks the DTR control signal needed to utilize the arduino's IDE auto-reset feature used to upload sketches, and you would have to use a well timed manual reset switch action to be able to use this module to upload sketches to a arduino board.
Lefty