Reverse engineering the Puxing PX888K programming format (1: The joy of soldering)

A while ago I bought a Puxing PX888K VHF+UHF radio HT. Like for many other radios, it's possible to change the configuration from a computer. Like for many others, the program is severely lacking in polish and only available for windows. To its defense though, it works more or less as good (or bad) running it through wine on Linux, as it does on windows. But it offers nothing like export/import CSV, or even though the channel list looks like an Excel sheet, it is not possible to copy or paste rows.

The perhaps default open-source radio programming software distribution CHIRP does not at this time support this radio model. Maybe, if I'm successful in my work, that can be changed.

First things first. To decode the data, I need to get the data. To get the data I need to listen on the communication wires, so a junction box was built. Given that I'm building with what I find in my parts bins, rather than routing a proper board and ordering parts, the final result does perhaps look more grown than designed. ...And that's not really false marketing.

junction box and schematic junction box back
The amount of switches comes from the fact that one of the serial cables I use for snooping is straight, while the other is a null modem cable, as I wrote, I'm working with what I have here.
Also, I want to keep my options open.

Since the radio is programmed with 5V signals, and the snooping ports work at RS232 levels, a level converter is needed. Again, lots of switches for connectivity options, and mixing SMT and through-hole devices oh my.

level converter and
simplified schematic
level converter back
A quick gander with the logic analyzer and a few attempts to read shows that the data is transmitted as regular serial 9600,8,N,1

action shot
To be continued...

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