Packet Radio with AVR

Posted on Aug 21, 2012

Here is some experimental hardware and software to transmit and receive AX.25 packets. It is essentially a PIC-E clone designed around a Atmel AT90S2313 with a few extra bells and whistles. I had picked up a couple of MXCOM MX-614s at the TAPR display (I also joined TAPR) at the Dayton Hamvention, and I needed a project to try them out on. I had designed many projects around Microchips PIC series micros, but had recently started experimenting with Atmel AVR micros. On the pic mail list this is referred to as 'going over to the dark side'. AVRs are PIC like risc processors, but with some additional features that made them slightly more suited for certain projects. AVRs are also very cost competitive against midrange PIC parts.

Packet Radio with AVR
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Packet Radio with AVR - image 1
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Simple flash based in circuit programming and cheap development tools also contribute the the attractiveness of the AVR processors. AVRs also code very well in C, but I'm still stuck with slugging away with assembler. Most of the AVR devices are available now from Digi-Key or other online sources. Digi-Key also stocks the STK-500 starter kit which is a great way to start working with Atmels for a very reasonable price. NOTE: This project is not intended as a PIC-E or MIC-E (I guess I could call it the AVR-E) replacement or competitor. It's just as another tool to further increase the utility of APRS. The hardware is pretty flexible, the example code implements a very basic UI-TNC, but you could easily edit out the console code, leave the AX.25 encode/decode routines to create trackers, WX stations or minimal function digipeaters. It should also be possible to implement an almost complete KISS modem, the main limiting factor is ram. The newer deisign no longer uses the PCF8583 I2C RAM/RTC. After the generous donation of some sample RAMTRON FM25160 fram parts by Klaus Hirschelmann I revised the hardware. We now have 2K of storage but no RTC. I simplified the Beacon function and used some of the additional storage to buffer incoming packets. I also made some minor changes to the hardware based on input from Klaus. Parts availability: If anyone has trouble finding some of the parts for the project, I have some spare...

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