This is a very interesting post. But I’m still missing some pieces of the puzzle. I’m trying to understand the relationship between FS2020, SimConnect, WASM, Gauge API, … I have googled like crazy, and have read many posts in this forum. But I miss the big picture. I’m still not getting it completely. How are things related to each other?
I’m also confused with some terminology. What does “gauge API” really mean. A “gauge” is an instrument in a plane, right? Or is there a different context when used for FS2020? If I want to control the FCU of the FBW A32NX, do I need that gauge API?
If I want to talk to the FBW A32NX in FS2020, do I create an executable that connects with SimConnect, can put in requests, and gets answers via some kind of callback function? And if I need this WASM module, do I talk to it through SimConnect, or does my executable needs to have some additional initialization and callback routines for this?
Bottom-line is that I would like to connect my proprietary hardware (based on PIC microconroller and via USB) with the FBW A32NX in FS2020. I have an own piece of software written in C# that is capable of detecting my HW modules (multiple), and is able to send commands (LED’s, 7-segment displays) and receive data (keypresses, rotaries, …). Let’s call it the “right side” of my software. Now I want to develop the “left side” that communicates with FS2020. Next to C#, I also have knowledge of C and C++.
I simply haven’t found a total explanation, tutorial, example or demo that shows me the big picture. I would love to see a schematic (don’t people make these anymore? 
).
I want to contribute as well. Once I have everything up and running, I might start a post to give a full explanation, to bring other newbees like me on the right track.
I hope somebody has the magic key to unlock the knowledge I need!