recommended volts and other newbie stuff question

So I have Arduino uno + mg2639 + em506(w/ shield):

1.)Is it ok to plug both dc and usb at the same time ?
2.)Recommended volts ?
3.)Is there an issue between the hardware

  1. yes
  2. info is in the Product page
  3. you will need to post links to the datasheets

...R

MG2639 D.s. https://cdn.sparkfun.com/datasheets/Cellular/ZTEWelink+MG2639_V3+Datasheet_V1.0.pdf
EM506 D.s http://cdn.sparkfun.com/datasheets/GPS/EM506_um.pdf

Links should be inserted with the full post editor. Go back and edit your post. That will make the link clickable instead of requiring a copy-paste.

Edited. Please check

Well the GPS module should be easy, particularly if you have a shield that someone else has designed to work. It has a 5V input voltage and should have no problem with 5V signalling.

That GSM package looks a little more difficult. It can't be powered from 5V and the 3.3V supplied by the Arduino is the bottom end of its allowable range. This is worse than you think because the Arduino can't provide a whole lot of power on the 3.3V pin and GSM communications are going to have some severe power peaks.

The datasheet for the GSM module doesn't say if its data lines are 5V tolerant.

Is it on some kind of carrier board or shield? That's a slightly awkward package to connect to. Does that carrier have any kind of power supply converter on board? Does it convert the logic levels?