Gareth,
Yes, the ESP32 is a great idea (we're leaning towards that in our production version), but there are a few challenges. It only has one 8 bit DAC, so no stereo audio, and crappy mono. The 3D audio is awesome, especially in a tailwheel airplane.
Also has a single I2C port, and the pressure sensors all use the same address. This may be different with the Honeywell sensors, not sure.
I've tweaked the tones on the oscilloscope for a while to clean up the audio and take care of all the little glitches when transitioning between the different tone frequencies. The ESP32 doesn't have the same audio library, so that needs to be re-developed.
GPS is too slow for calibration purposes, we don't need or use one.
AOA becomes weight dependent if you use differential pressures for your coefficient of pressure. You can normalize with q (Pfwd-PStatic), most AOA systems do) but you now rely on the static ports which on most airplanes are out of whack, and also misread in a slip/skid. There's an FAA paper out there comparing a bunch of different unnamed AOA systems on the market. The ones that don't normalize properly are weight dependent and worse than useless.
You don't need a display, however I find that it's very useful to have one for a crosscheck.
You can use Efis data instead of using the internal IMU, but our goal is to have this system work in any steam gauge airplane and also provide a backup attitude and air data.
We do use the IMU for acceleration data (G limit warnings), 3D audio (lateral acceleration), gyro rates are also used by the calibration wizard.
There are a lot of considerations that went into this system to make sure the math & physics are correct, not to mention hundreds of hours of test flying with multiple airplanes, a lot of it using a flight test boom and a tactical grade IMU (VN-300). So if you change your sensor setup I suspect you'll be in for a lot of learning :) We have lots of data we can share if you are interested.
Our Gen2 v1 box was a much simpler system. Teensy only, no wifi, RS232 chip for reading the Efis stream, single audio channel, two differential pressure sensors, no baro. I may even have some of those boards if you want to build one. Attached the schematics.
Onspeed Gen2 v1 schematic
