On Wednesday, August 7, 2019 at 9:30:04 PM UTC-4, M S wrote:
At 21:57 07 August 2019, Martyn Johnson wrote:
SNIP for brevity
I have a Colibri II and run XCSoar on a Kobo; the GPS data goes Colibri
to Kobo; the declaration goes Kobo to Colibri. The cabling is homemade,
based on the specs available. It helps that the serial connection (wired
onto the motherboard) to the Kobo is TTL like the Colibri. The driver
used on XCSoar is LXNav.

Not sure if this helps, but at least it shows it works.

Yes this helps! I am running Top Hat (a variant of XCSoar) on a rooted
Nook, and I expected I might have to go where you have been. I expect I
can find that wiring and setup on the Top Hat site, but I'd rather keep the
Nook running alone at this point because it's been reliable using an OTG
cable and USB GPS mouse.

Similarly, I use Tophat on a Nook. The OTG method proved unreliable. More recently I got a PowerFLARM, so I added a serial port into the Nook and connected to the FLARM with a cable. Now the FLARM is the GPS data source for Tophat, and, if I edit a task on the Nook then Tophat asks if I want to "declare" it, if I say yes then it sends it to the FLARM and it appears in the (IGC-approved) flight log generated by the FLARM. The Colibri communication protocol may differ, but try it. The hard part was hacking the serial port into the Nook, but mostly because I needed RS232 voltages for the FLARM. If your Colibri uses TTL levels then it's a lot simpler.
https://www.tapatalk.com/groups/toph...p?p=2353#p2353

If there is somebody with the right setup nearby, try borrowing such a device and see if it sends the declaration into your Colibri.

But I am surprised that editing the task manually on the Colibri doesn't also make it a formal declaration. Maybe there is an extra step you need to do in its menus?