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Basic Analog Input Circuit and Program


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#21 Chris Walker

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Posted 26 February 2011 - 09:05 AM

Extremely helpful, thanks. Last questions… :). I have changed my voltage to 3.3 and added the AREF lead as well. I now measure my input lead at 2.9 to 3.4V. Is that too high for an input line?

That's in the right range, but technically 3.4V is a bit high. According to the microcontroller datasheet, the analog inputs shouldn't go over the AREF voltage. I can't say that it would hurt your board or not...but it's out of spec.

If I wanted to use a voltage divider I understand implementing a resister but I do not follow the Max Range Value? Where did you get those numbers 1350, 1023 and 1550? I assume this adjustment is needed to regulate my sensor values because I dropped voltage?


I used 1350 as an example to recalibrate the 0...1023 range. If you take 1023, diving it by 2.5 (the new "top voltage") and multiply it by 3.3 (the old "top voltage"), you get 1350. 1550 was a typo...my bad :)

If you are supplying 3.3V to the sensor and getting analog values in the 0-3.3V range, then no need to recalibrate anything. Just set the range to the range you want (that makes sense for the sensor) and you're good to go.

Chris

#22 Ckiszka

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Posted 26 February 2011 - 09:21 AM

That's in the right range, but technically 3.4V is a bit high. According to the microcontroller datasheet, the analog inputs shouldn't go over the AREF voltage. I can't say that it would hurt your board or not...but it's out of spec.



I used 1350 as an example to recalibrate the 0...1023 range. If you take 1023, diving it by 2.5 (the new "top voltage") and multiply it by 3.3 (the old "top voltage"), you get 1350. 1550 was a typo...my bad :)

If you are supplying 3.3V to the sensor and getting analog values in the 0-3.3V range, then no need to recalibrate anything. Just set the range to the range you want (that makes sense for the sensor) and you're good to go.

Chris


Perfect! Thanks :)




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