Sunday, July 30, 2023

New probe wired into N291DR

Today, I did the necessary legwork to get the new probe wired into N291DR. The way it's set up, we are tapping into the +12VDC supply to the nav lights, and (still) using Wi-Fi for sending data to the display.

The AoA and airspeed worked really well. The yaw angle differed from the inclinometer ball by maybe a degree or two -- I just set it by eye, so I'll tweak it to be centered. Other than that, it worked like an Airball probe and did its job. Yay!

Of course, no test would be a test without squawks. Here they are:

Flaky Wi-Fi. Sometimes, I connect the display to the probe and the data rate seems low. I power cycle one or the other side, and it self-fixes. I think there may be an issue with the Wi-Fi base station implementation on the ESP32, or something. I hope it's easy to fix. Eek! I will try to repro on the bench.

Weird altitude readings. The altitudes on the display were maybe 100-200 feet higher than the rest of my instruments. I cargo culted some kind of temperature correction in my altimetry calculation in the display; that may be the culprit. I need to clean that up and use the standard conversion formula, and see what that yields.

Probe inflight autozero is a disaster. If the probe is power cycled in flight, it tries to autozero, using whatever large dynamic pressure readings it's getting, and is basically useless for the rest of the flight. I need to program some more cowardice into the algorithm, refusing to autozero if there is significant pressure on the sensors. Extra credit: See if I can store the latest offsets in some NVRAM, if the ESP32 has any.

Ball "trails" don't seem visible. For some reason, I have lost the "trails" / "history" the ball leaves behind. I can't think of why. Need to debug -- might be some stupid mistake somewhere.

USB malarkey. The USB connectivity from the display to the control "knob" remains as gefurfified as ever. Just waiting for that new display with bated breath...

I am hoping that the basic static pressure measurement scheme is solid. Otherwise, I'll have to go back to fabricating some kind of static pressure "spike" like the older models, and that's really a total pain to manufacture. Fingers crossed.

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