I need some help in selecting a GSM/GPRS shield from two possible choices.
Shield 1 : eBay link
Shield 2 : eBay link
The main difference is the powering of the shields.
As you can see, "Shield1" has a power jack near the antenna.
"Shield2" looks like any other ordinary arduino shield, and doesn't have any external power connection.
First, I thought that "Shield2" is better, because it is much more portable, as I only need to power the Arduino. But in the description, there is a strange part (red text): "Because SIM900 peak current more than 2A. This shield must work with a external DC9V power supply." There are also other sellers (like this or this) and they are all saying that the SIM900 needs 2A current. After reading the Arduino UNO Reference, I don't think this board could survive this amount of current. Or I just don't understand something?
Can someone please explain me this, and help me choose between the two shields?
Yes the SIM900 can draw up to 2A, that will not be possible from the host Arduino's 5v.
But that shield appears to have it's own switching regulator so I assume it gets power from VIN. As such it might be ok as long as your power supply is up to the job...
...I just looked at the schematic for the 2nd board, they seem to be regulating down to the 4v1 from the Arduino's 5v, I don't see how that can work well, it will be OK most of the time but when transmitting and drawing 2A that will be a problem.
Unless I missed something I would avoid that board, it doesn't make sense to draw that amount of power from the Arduino's 5v source.
Hi Rob, thank you for your help!
I just got a reply from the sellers of both shield.
Seller about "Shield 1":
"This shield can power Arduino. [...]" Is this possible? The shield will power my Arduino, so will I only need one power supply? This sounds acceptable.
Seller about "Shield 2":
"SIM900 get power from MIC29302WU not direclty from the arduino main board. It's peak current only keeping a very very short time. So it's safe to the arduino board. We have sold many this shield. all works fine."
What do you guys think? Would you choose "Shield 1" or "Shield 2" after this?
I can't really tell if either will work, however this one
at least has pretty good documentation.
AFAICT from the schematics they get their power from the Arduinos 5v, that doesn't make much sense to me but maybe it works because the transmission times are very short. I don't know why they use the 5v pin when the VIN pin is nearby and that would be OK to use.