Making Raspberry Pi HATs for fun seems to have become a popular hobby, as after checking out Leon Anavi’s Infrared pHAT a little while ago, I’ve just come across Nadhat add-on board with GSM/GPRS and Bluetooth 3.0 made by Frederic Pierson in his spare time.
Nad stands for “Network Access Device”, and the device comes with the following specifications:
- SIM800C module with 2G GSM/GPRS support, and Bluetooth 3.0 + EDR (but Bluetooth is not mentioned by the developer, so it may not work right now)
- SIM card slot + connector for GSM antenna
- CR1225 cell battery slot for RTC
- 40-pin header provided, but not soldered
- Dimensions – 65 x30 mm, compatible with Raspberry Pi Zero
He explains that he made the board himself and the PCBs “are leaded reflow processed and do not follow regulations in Europe”. You’ll also have to provide your own GSM antenna and CR1225 battery. He’s released some files on github, the datasheet for the components, the schematics – but in PDF only, why? – , and the software directory only contains a short script to power up SIM800C.
The cellular module is attached to the Pi via /dev/ttyAMA0 serial interface, and you’ll have to send AT commands to control it. He also checked out 3G and 4G support as some people asked possible due to 2G sunset, but the modules he found where both expensive, and much bigger than the 2G modules, making it impossible to fit into the RPi Zero form factor.
Since the board is just a hobby project, it will probably never be manufactured in large quantities, but Frederic made a few boards himself, which you can get for 49 Euros + delivery if you are interested, and boards are still available.