GPRS Shield1.2 and FEZ Domino reboots sending data over GPRS

I’m using the SeeedStudio GPRS Shield 1.2 ( and the FEZ Domino to GET or POST data to a website over GPRS. I’ve used both methods that the modem supports (GPRS commands and the embedded HTTP commands) for communications. Both methods work well.

However, sometimes while communicating, the GPRS shield causes the FEZ Domino to reboot.

I’m using a 9V 3A power supply which should provide plenty of power to the FEZ Domino and the GPRS shield.

Anyone have any idea what might be the problem?

How hot are the regulators? If you can leave your finger on it for 5 seconds then it is okay


Since the issue is intermittent, I’ll need some time to reproduce the issue. I’ll check the regulators when the issue occurs and not occurs and let you know. It may take me a couple of days.


You do power the setup via the GPRS shield, right?

Yes, powering up and using the shield is not a problem. The FEZ Domino was rebooting periodically when I tried to transmit data over GPRS. It didn’t happen all the time and texting never exhibited this behavior.

I got a new board from SeeedStudio and I can no longer reproduce the error. So, I’m chalking it up to a bad board or a bug in the Sim900 firmware.

A couple items come to mind after reading your post.

  1. In your development / debugging setup, do you have the GPRS radio nearby? I’m using a 50W base station and external antenna and have had to tune-down both the output of the HT and the replies from the base station when the Domino is within close proximity. You might want to consider a Faraday-style enclosure.

  2. If you have a fast-sampling Digital Multimeter, attach it to the power feed since you are using the same power supply for the radio and the FEZ Domino.
    A. Look for transients induced by poor SWR into local ground
    B. Watch for voltage sag when the GPRS radio keys up.

  3. Post your COM handler code. I’ve seen a number of problems with serial port code samples posted here and in other locations. If your COM handler isn’t set up correctly, all kinds of bad things can and will happen.