I have 400 pressure sensors with ~500k~1M ohm resistance. The goal is to measure all the readings in 10ms or less. What are my options?
Could You make a drawing showing every connection and pin used? Pen and paper would do well. Please also post the code using IDE autoformat and forum code tags, </>, when pasting.
Yes, I added the schematic and the code snippet.
I'm not well versed in the ESP32 however at least one version has two A/D that can convert at the same time. If this is correct you could use them to cut your time nearly in half.
However you specified "..D34 ADC pin ..." so I'm not sure if that was relevant or not.
If you can't use the two converters for some reason than you could consider external converters 2,4 .....etc.
pressure sensors with ~500k~1M ohm input impedance ..
Not to be picky but pressure sensors do not have an input to have an impedance of, so I'm not sure what you are saying here.
I also believe you are running the HC4067 at 3.3 volts. I would think the resulting higher on resistance would be significant but you might want to check if the issue is in the HC4067.
Intuitively I feel your approach may not work.
can you give the spec or a link?
If that was on the input to the ADC - with the signal being switched at 250us - it would be horribly confused!
Also be aware the ADC on the ESP32 is cr .... not very good.
Perhaps a better approach would be to use multiple stand-alone ADC's with multiplexed inputs?
Code snippets are of no use . Always post the entire code.