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Electronics => Electronics => Topic started by: mstacho on October 27, 2011, 07:56:39 AM
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Howdy,
I'd doing a project now that requires me to read 16 sensors. There are 2, 4-pin addresses, call them A and B. It is essential that only one pin in set A and one in set B are being read at one time, or else the current will spill over and you get washed out sensor readings.
So here's my question: I have set A connected to ADC0 through 3 on the Axon. If I understand it correctly, the ADC's should just be multiplexed, right? Or is there some weird spillover effect that I'm not aware of? My sensors have that washout I was talking about and I want to know if it's due to my setup on the Axon or if it's due to my setup to read pin set B (which is being done with a 4051 MUX chip).
Any thoughts?
MIKE
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Are you reading the channels using single conversion mode or free running mode? If you're using free running mode there's a note in the data sheet that points out you need to skip a conversion. I don't have the reference handy right now, but it's due to the fact that the channel has to be changed before the next conversion starts. If you're changing it in an ISR, the next conversion has already started, so the second and subsequent conversions are off by one. You need to drop the second conversion, and then things will be in sync.
Sorry if that's not it. I'm not sure what the problem you're seeing is.
Joe
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Hm...now that I've run more experiments (and have tried what you suggested), it looks like the problem is actually in the other set of pins -- it's my 4051 MUX that's screwing up. Oh well. I guess it's back to the drawing board :-P
Thanks for the info,
MIKE