Tim Watterton posted an update

More build details

The following info might be helpful if you want to reproduce the build without any soldering:

  • The GSM shield I used is a common design based on the SIM900 module, like this one. The jumpers need to be set to use D0/D1 for the serial pins. D9 is used to power the shield on, and might need a jumper setting to enable it - the module has a power button that you can press manually instead, if required. The shield has a regulator on board to provide 4.1V for the SIM900, and the electrolytic capacitors I added provide an extra 6000uF of capacitance on this 4.1V supply to support peak currents. This allows the GSM shield to run from the shared 5V supply. As an alternative to fitting these extra capacitors, you can connect an external power supply directly to the GSM shield (the 4.1V regulator is fed by either this external supply or the 5V shared supply).
  • For the GPS functions, you can use a standard GPS shield, with the the serial lines on D7 and D8. I actually used this U-Blox VK-172 GPS USB stick, which I modified by removing the USB plug and soldering a couple of wires directly to the UBX-G7020 chip, with 100 ohm series resistors. Pins 18 and 19 provide the serial Rx and Tx lines (at 3.3V). This is a cheap way to add GPS functionality!

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