This is an old project of mine with limited documentation or images.
Background and Design
Because I had so many issues with my V1/V2 APRS Tracker PCBs, I decided to take a step back with this one and not try to make it so small and custom. I extended the layout to all be on one side of the PCB and replaced the custom ATMega328p layout with an off-the-shelf Arduino Pro Mini. Again please ignore how bad the schematic is, I was still 14…
Assembly and Results
Assembly actually went really well. The PCB came out very clean and there didn’t seem to be any sort of design issues or anything. From what I remember, it worked very well, and my only issue were challenges with the RF from the transmitter causing the MCU to glitch and for the PTT line to be held high. I don’t remember exactly how, but I was able to fix this. I took it on drives around with my family, and actually had my dad take it with him while he was flying his small plane, and it tracked and worked perfectly. Stepping back from making the tracker as small as physically possible was definitely a good move and I learned a lot from this design.
Modified V3 With Teensy 3.5
This and all past versions originally used a standard ATMega328p with a library that used 4 pins and some filtering circuitry to circumvent the limitations of the DAC to generate AX.25 AFSK audio that could be fed into the transmitter. Eventually, I came across this dead-simple library for the Teensy microcontrollers that uses their higher-end DAC to directly output AX.25 audio without the need for additional circuitry. I had to port it to my Teensy by changing a few pin definitions but it ended up working really well. I assembled a second V3 PCB and soldered on my Teensy on top of it instead of the Arduino Pro Mini. Here you can see the Pro Mini and Teensy versions next to each other.
