You may not be looking for a new cell phone right now, but someone has just managed to transform his Raspberry Pi (RBPi) into a working cell phone. David Hunt has used only off-the-shelf components and put them together for the project. Although it is not as slick as the regular cell phones available in the market, at about $160, David has created a one-off project that certainly has no economics of scale working for it. The best part is all components of the phone can be taken apart at any time, used for some other projects and then reassembled. Can you do that with your regular cell phone?
David has called his cell phone the PiPhone, in honor of the base RBPi that powers it. The other major parts used for making the PiPhone work are a Sim900 GSM/GPRS module and an Adafruit touchscreen interface. The GSM/ GPRS module allows the cell phone to make and receive calls, while the touchscreen provides the user interface. A 2500 mAh LiPo battery powers the entire contraption. The GSM module connects to the RBPi through a UART, while the battery fits in between the TFT screen and the RBPi, allowing the PiPhone to work standalone, without wall warts or dangling wires.
The touchscreen interface has a numeric keypad displayed on the screen. After dialing the required number, you need to touch the phone icon at the bottom to make the call or hang up.
The Sim900 GSM/GPRS is an intelligent module, which oversees the entire communication process of the PiPhone, including sending the standard AT commands to the RBPi for making calls, hanging up and sending text messages or data. Towards the bottom of the PCB is the connector where you can insert your SIM card. Therefore, you can use a regular prepaid SIM card available in the local phone store.
Just below the GSM module, there is an on/off switch and an off-the-shelf standard DC-DC converter. This converts the 3.7V supplied by the battery to the 5V required by the rest of the electronics. Heat dissipation was the only problem that David faced because of sandwiching the RBPi, the TFT, battery and the GPS module together. During development, as all the components were placed apart, they remained cool to the touch even after extended periods of use. However, sandwiching prevents air from circulating within, resulting in the CPU getting a bit warm after switching the unit on for a few minutes.
The GPS card is insulated from the RBPi with a thick foam-core board, allowing no accidental electrical connections between them. David used a couple of cable-ties to hold the different parts together.
Of course, walking into a local phone shop and picking up a normal smartphone would be simpler and cheaper, but that would not be as much fun as making your own. Moreover, as said earlier, you can put the parts to other uses as well, which you cannot do with a standard phone.
David has put up all his code and instructions on the GitHub. There are links available to instructions on installing the TFT.
