First - it was lovely to see the Pi-on featured on the Hackaday blog a few weeks ago! (https://hackaday.com/2019/08/03/raspberry-pi-helps-vintage-psion-find-its-voice/)
Since then I've been tinkering about a bit. With the help of the Comms Link I downloaded a word processor to the Organiser. It's called AutoScribe Plus, it was sold by Widget UK (now defunct) in the late eighties/early nineties and it's actually rather good. (Well, it's as good as a 2-line word processor can be!) Widget gave permission back in 2002 for Psion users to distribute their old software freely, so if you have an Organiser II and wish to process words with it, head over to https://www.jaapsch.net/psion/packs.htm, pick 'Autoscribe Plus v5.11' and enjoy.
I even managed to get the Organiser displaying web pages (in pure-text form of course) using the w3m text-mode web browser on the Pi. The Wikipedia home page, BBC News page and the retro Hackaday homepage were all view-able.
Unfortunately some of my soldering surrendered last week, so the Pi-on is now out of action. This led me to think - could I replace the RS232 serial cable connecting the Pi and Psion with a Bluetooth module like this https://tinyurl.com/y5fs4e9q? This transceiver can convert Bluetooth signals to 5V TTL signals and vice versa. The RPi 3 has Bluetooth built in, so it should be possible to wire this chip up to the Comms Link, provided I can find how to supply and receive 5V TTL signals (as opposed to 12V RS232 signals) to/from the Comms Link correctly.
I've dismantled the Comms Link and I've managed to 'insert' a 5-volt TTL signal from an Arduino's serial pins to the Comms Link board, so that the data is received properly on the Organiser screen. Now I need to work out how to 'tap' outgoing 5-volt TTL signals on the Comms Link board before they get converted to RS232 and sent down the serial cable. Here's a hopefully not-too-confusing summary of what I've just attempted to describe!
Injecting 5V TTL data into the Comms Link :
serial cable --> 12V RS232 --> 5V TTL (have managed to 'insert' signals here from an Arduino) --> Organiser
Tapping 5V TTL data before it gets converted by the Comms Link:
Organiser --> 5V TTL (need to 'tap' the signal here) --> 12V RS232 ---> serial cable