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This post will likely seem like a rehash commercial praise of Adafruit, though I only mean it to record the basic information for a DIY mobile phone.
lady ada over at Adafruit has a guide for a DIY mobile phone project. It looks about the same level of complexity as the PiPhone, except explicitly with an Arduino instead of an ARM system-on-a-chip controller. The parts for the entire guide total up to about 120$US. For a 3G radio, it costs around 30$US to 40$US more, depending on the GSM module.
The basic kit involves the following parts:
- [Adafruit FONA 800 shield](https://www.adafruit.com/product/2468)
- [Adafruit TFT Shield w/Resistive touch](https://www.adafruit.com/product/1651)
- [Stacking headers](https://www.adafruit.com/product/85)
- [GSM SIM card](https://www.adafruit.com/product/2505)
- [1200mAh LiPoly Battery](https://www.adafruit.com/products/258)
- [Metro 328](https://www.adafruit.com/product/2466)
- [Wired electret microphone](https://www.adafruit.com/product/1064)
- [Small metal speaker](https://www.adafruit.com/product/1890)
- [A plug-in headset](https://www.adafruit.com/product/1966)
Essentially, to reiterate the design, the phone has a touch screen interface to the main controller, in this case the Metro board. The main controller then tells the GSM to make calls, and if I understand correctly, to pass SMS messages, and to receive events such as incoming calls, messages, and GPS information if the GSM chip has it built-in. The actual call audio happens via the GSM chip, as far as I can tell, though because these GSM chips also handle data, some of them 3G, the main controller should also have the ability to VOIP.
At this point I have not actually started building anything yet, for either the Arduin-o-Phone or the PiPhone. Still waiting for parts.
From a freedom perspective, the FONA 3G GSM module, for example, has links to drivers and hardware specs. I have not seen the explicit license for the GSM module. I delayed this project many times while looking for the best case for libre hardware and software. I think this finally gives a sufficient set, a little better than the PiPhone which lacked some explanation of the GSM module itself. However, using the resources from Arduino and Adafruit I think I could just combine the better parts of each project.
Note particularly for that module: lady ada recommends beginners start with the FONA 80x series, so for the moment I will probably mind that advice.
At this point, I feel like the form factor of the assembled device should come in quite a bit smaller than I originally envisioned. Perhaps closer to a double-deck of cards instead of a 1980s phone.
2 References
- [PiPhone](https://github.com/climberhunt/PiPhone)
- [Adafruit DIY Arduino Phone](https://learn.adafruit.com/arduin-o-phone-arduino-powered-diy-cellphone)
- [Adafruit-METRO-328-PCB Hardware source files](https://github.com/adafruit/Adafruit-METRO-328-PCB)
- [Adafruit FONA 3G Cellular Breakout](https://www.adafruit.com/products/3147)
- [Adafruit FONA 3G Cellular + GPS Breakout Downloads](https://learn.adafruit.com/adafruit-fona-3g-cellular-gps-breakout/downloads)