GSM Shield powering


I have the ITCOMSAT 1.1 GSM Shield, and I'm trying to use it with Arduino Pro Mini, so not as a shield. I noticed that if I try to send some data by httpPost once every 20 seconds, with the arduino pro mini powered through USB, one requests makes it and the next one, not. I assume that the SIM900 simply doesn't have enough power.

Also, if disconnect the arduino from USB and connect 12.3V to RAW and GND (rated max. 2.5 A), (and connect RAW, GND, and VIN pins from Arduino to the corresponding pins on the shield (as if it was UNO), the SIM900 turns off. This is very weird to me.

Can you help me power the shield properly?

Thanks a lot!

EDIT: I changed the time interval to 40s and now it's all ok. But I still need to send some sample data every 10 seconds...

Check which GPRS sending mode you are using. If you transmit just one out of the possible 8 timeslots you ease the load on the power supply. It will be a slower transmission but safer, power-wise. For the Quectel module there is a special (non-standardised) AT-command to set the GPRS mode, your module might have a similar command.