Monday, August 29, 2011

Data transmission by using the phone display

Most wares I build up are highly experimental prototypes. Often they have no display and not a full keypad for input the settings. At the PC RS-232 or similar simple cable-based protocols can be used to transfer setting to the ware. But if you want to use your present-day phone there is no established way expect using Bluetooth or wireless LAN, which is quite expensive.

So I came up with the idea to transfer data by flashing the phones display and implemented the corresponding hard and software. The result is a phone-programmable igniter that can be programmed to any time in the future (theoretically several year).

The hardware is kept extremely simple. It can be power by two 1.5 V-batteries. Nevertheless it has a "included" real-time clock and consumes very small amount of power. The receiver is a simple photo transistor. Here you can download the source for the micro controller (Attiny 44 A from ATMEL).

The picture above shows the front window with the photo transistor behind on the left. On the right you can see the 6-pin header for flashing the microcontroller.

The case is made from a steal profile with end cabs thermally formed from a PVC-Pipe. The following image shows the complete circuit.

For sending the time/date to the ware I wrote an App for Windows Phone 7. It sends an 32 bit number and 4 parity bits. With the used Biphase-Mark-Code around 18 Bit/s gross throughput is possible. The C# source for the sending app can be downloaded here.