I've done a test layout to play with that I'll be testing in the next few days. Below is the layout.
I've gotten ton's of emails (100 or so) about the code for the APRS node I've been hacking away at. I normally use an Arduino type board for prototyping. However, the code is in C. I do sometimes use processing to quick test something but generally things destined for the embedded world are in C. Below are some projects I found related to what I am working on. Some use the CML chips some don't. In the low cost model I don't use it. I have been playing with a CML chip for digital type radios but they drive the cost up with what I am attempting to do which is build a device within the reach of just about any public safety department in volume. And please if you don't mind, post questions as comments rather than emailing me directly. That ensures that any Q&A can be seen by everyone.
http://garydion.com/projects/whereavr/ - This is a really nice setup, different application but very tidy setup.
http://sites.google.com/site/ki4mcw/Home/arduino-tnc - Hope to see more from this. Its what more of you are looking for with PDE files provided.
AX.25 encode is complete and seems to work well. AX.25 decode works, but I have a special mode and also have a CTCSS listen setup to remotely turn on that mode. Still some items to do , but its almost time to put this on a board. If you are interested in this project please let me know. I was able to get my Brother Laser printer to work with the toner transfer method after some trial and error. I had great results using a Brother HL-4070CDW and Kodak inkjet photo paper using a iron and being very patient with the soak.
I have several radios that don't have CTCSS or the ability to page out fire tones. I figured I'd solve it with a programmable AVR. I started with a basic Arduino board and progressed to c code to control various circuits for the generation and detection of tones. I'll be posting some pics and information soon.