The unit has been tested through the weekend and I'm really happy that it worked! Unlike previous attempts, when proprietary GPS units couldn't handle freefall, this time GPS data was displayed during all phases of the flight.
Update was to 250ms and unit reaction time was pretty accurate. GPS unit rated up to 5Hz, with time it will be upgraded to 10Hz (same as in FlySight)
I didn't have time to order tinted tape, so I put black one on the back, and on a bright day digits were readable no problem at all.
Despite digits being blurry (the image attached is pretty close to what's in reality) it was easy to read them during the flight. Display is not distracting and could be looked at with quick eye movement. You might need some practice on the ground first just to get used to it, but then during the flight it didn't take an effort to check speed.
As promised, basic source code and hastily written assembly instructions:
https://github.com/RomanTheLegend/WingsuitGps
Contributions are welcome because I won't have enough time to develop this project at a good pace, and there are few quite complex functions to be implemented.
Next on the ToDo list:
* Make few more units for my friends for wider testing and feedback (mid-October because shipping is only from China)
* Make 3D models and wiring cleaner and leaner
* Explore the possibility of attaching some control switches - that would allow to write some kind of menu interface in the future
P.S. I got carried away a bit and added Bluetooth intercom made from old cheap headset while at it. This helmet gets more and more advanced