I've wanted to build a radio-less node because sometimes it's easier and makes more sense than a radio-based node. Also, sometimes iaxRpt is a pain (e.g. fails to register with Asterisk, network latency issues, etc). But I wanted to make it look as much like a radio as possible.
This build is a bit more complicated than the super awesome and super simple MPow-071 Headphone hack. I love that hack and want to build a "radio" based on that at some point. This project is not that... because I wanted to manipulate Asterisk is direct and different ways.
Fob modification is for fools. Most importantly I wanted to avoid modifying the sound fob because the Pi has GPIO pins for a good reason: they are to be used. If you want to solder small wires to small chips on the fob, have at it. I still think it's a needless and clumsy workaround.
The radio carcass
I picked up this "for parts only" Motorola radio on Ebay for cheap. I was hoping there would be enough room to shoehorn the Pi and needed extra hardware and wiring. I lucked out! I was able to remove all of the radio's boards and that left all of the inside space for installing hardware.
(images of gutted radio)
Parts is parts
With the radio gutted, we could start installing the needed boards for the system:
RaspberryPi 3A+ -- most favorite Pi board aside from the PiZero. Does the job of the 3B+ without the latter's crappy power management issues and with only the single USB port needed.
Syba Sound fob CM119 chipset UNMODIFIED -- plug this into the Pi running HamVoIP and audio is piped out by default. That's a great sign. Is audio in on by default??Amazon Link (2021-09)
Microphone -- for that talkie talkie. Pick one you love. It will probably need modification.
Audio amplifier board -- the Pi Audio out will not drive the radio's built-in 4ohm speaker. You could replace the oval speaker in the faceplate. But it seems better to drive the audio into a louder amplified speaker for noisy environments.
Configure rpt.conf events stanza
OPTIONAL Modify Supermon... for fun
This quick modification to Supermon's link.php file allows you to PTT from the Supermon web page.