Saturday, December 16, 2017

Flakey sensor or circuitry again

After gaining confidence that, with proper ESD protection, the probe circuitry was not destroying my sensors (any more), I installed 2 more sensors for a total of 3 (alpha, beta and dynamic pressure) and went out for a road test.

After a few minutes' worth of run time -- some of it when parked and raising the mast, and some at the beginning of my road route -- the probe stopped sending data. It resumed momentarily after a minute or so, then stopped again and did not restart.

I had my computer handy so I did some debugging, and it turns out that one of the sensors was freezing up. It enumerated properly on the I2C bus, but when asked to give a pressure reading, it hung in its "waiting" state forever. The other two sensors worked fine.

Power cycling the probe did not help immediately. Note, from previous work, that the probe remains powered up to some small voltage due to the battery, and I did not remove the battery.

Later on, after leaving the probe off for a while and turning it back on, it started working again magically. Note again from previous work, that when turned off with the battery connected, the probe VCC dies down to a small amount over a few minutes, then remains at that small amount thereafter.

My current provisional conclusion is that the sensors are flakey, either because of how I am using them, or some detail of my circuit, or some internal issue that I am running into. I do not currently have an obvious way forward apart from an extensive re-design of my electronics and/or extensive debugging of the problem hoping to reproduce it.

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