PI TNC - progress report.
For those fairly new to the group, I have been working on a TNC for use with the pI that is the same size as the pi and plugs into the expansion header. The prototype was a TNC-X, with a 26 way header superglued to board. There is a photo of it on the home page of this group.
I've now received the first PCB's, and built a couple. There are photos at https://dl.dropbox.com/u/31910649/S1300001.JPG and https://dl.dropbox.com/u/31910649/S1300002.JPG. The TNC is largely based on the TNC-X, but I've replaced the serial port with an i2c connection, so more than one can be connected to the PI. The current board has a mini-DIN radio connector, but I find mini-DIN plugs very difficult to wire, and the connector is just too high to stack properly, so the final version will probably have a DB9. I've written a linux driver that takes the i2c data stream, and converts to a pty that can be used with the normal linux ax.25 kissattach program. All this seems to be working.
I've a couple of developments in the pipeline. One is to replace the MX 614 modem, hopefully with a PIC based solution. Although the 614 works very well, it is relatively exensive, and only works at 1200 baud. I hope to be able to run at 300 for HF use. I've also bought a couple of RFM22B modules. These are tiny 100 mW 434MHz data tranceivers - see http://www.sparkfun.com/datasheets/Wireless/General/RFM22B.pdf. I plan to do a version of the TNC using this module.
A version using the FX 489 modem for 9600 baud links is planned, nut I haven't started work on that yet.
73, John G8BPQ