ADC conversion question

[wolverine_349]

I am using the 10bit ADC off the 16f689 for some simple conversion and this is what i get:
actual analog voltage off mutimeter=0.65V
reading from the adc =0.5674V
if analog=0.66V,digital =0.57V
and if the anlog voltage increases the digital value goes far and far from the anlog value

this is how i interprete the voltage off the ADC code

[Storic]

I am also reviewing my analogue coding, I had lots of movement where I was getting different reading all the time from the same ref input. Have you considered http://www.ccsinfo.com/forum/viewtopic.php?t=19509 Filtering your analog input with code as describe.

Andrew
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What has been learnt if you make the same mistake?

[SherpaDoug]

I would first print out the A/D reading in hex and make sure that is stable and tracks the analog input. Once you know that works then you can worry about the math.

On the other hand "decivolts=(y*MAX_VOLTAGE)/1023; " looks bad to me. If y is a long int then I would expect y*MAX_VOLTAGE to do an integer multiply, effectively truncating MAX_VOLTAGE to 4. The /1023 may also be an integer division, the list file will tell you for sure.
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