I’ve got the above Waveshare converter to work 
, so now I can monitor my Outdoor Unit in comfort, and for less than £25, so @glyn.hudson I can now return your MIM-C02N if you’ll PM me your postal address.
(I’ll do a write-up of the hardware/software/connection details in due course.)
Edit: This write up can be found on the Monitoring Your Samsung ASHP Controller thread.