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.
I started this project months ago with the goal of having software and hardware that could be used in the field. I have it working on the bench and a very crude setup that I can attach to either my TM-V71a HAM radio or my LMR based TK-3180 handheld for search and rescue. I’ll need plastic and not just any plastic but something rugged. I plan on continuing to write more code with the crude version to add some public safety specific features as I have completed 99% of HAM related operations. If you would like to build one of these to test with and help improve the code and hardware please let me know. The next evolution will be a plastic housing and some redesign to make it as small and low power as possible.
I’ve been testing a small display I used in a previous post for use with APRS using a AVR. Using a simple R2R DAC for the modulation and zero cross detect seems to be working at 1200 baud in a reliable fashion. While I have this working laying on the desk in many pieces, I’d really like to look at taking this prototype to something I can put on in my truck or better yet in my pocket. Here is where I’m headed and if anyone else has ideas, comments, etc.. post it.
ATMEGA 644 This has just enough pins to drive the display and do the I/O. I’m trying to keep this as cheap as possible so that its easy to get into.
No external modem IC. Zero Cross Detector and R2R DAC or small DAC IC.
Small backlit display that can display at least 4 lines of text.
Function with or without a GPS. My focus is messaging and identify who is within range of me. One of the best things about APRS is the ability to find who’s out there. It’s not just about tracking.
Port for a ps2 keyboard. I want to use this for messages.
Can be powered from AA batteries or 13.8VDC.