That is correct - the A/D count will not change (maybe 1 count) since you have something like a bridge configuration. If you want the A/D reading to be stable & accurate you must either control the Vcc to the PIC within the required accuracy, or supply an reference voltage (using the appropriate bits in the config. register). Roy J. Gromlich ----- Original Message ----- From: "Robert Mash" To: Sent: Monday, January 26, 2004 1:54 PM Subject: Re: [PIC:] 12f675 a2d supply voltage dependancy? > Let me express it like this... > Two equal valued resistors form a voltage divider between 5v and gnd. > The pic is powered by the same 5v and gnd too. > The junction between the two R's is repeatedly sampled with the pics' a2d. > The a2d is set up with gnd as the reference, and the two lsb's ignored, > resulting in a value of 127. > Now, for some reason, the supply voltage changes upwards 1% to 5.05V. > Does the resultant value from the a2d on the next sample stay at 127? This > would imply that the successive approximation a2d has no absolute voltage > reference, and is dependent on supply voltage. > > Robert Mash > > ----- Original Message ----- > From: "Jan-Erik Soderholm XA (TN/PAC)" > To: > Sent: Monday, January 26, 2004 1:39 PM > Subject: Re: [PIC:] 12f675 a2d supply voltage dependancy? > > > > Robert Mash wrote : > > > > > -List, > > > -Anybody know if PICs' internal a2d is dependent or > > > independent of supply voltage? I didn't see anything --in > > > the datasheet for the 12F675 that led me to believe either way. > > > - > > > > Hi ! > > > > Define "dependant". > > > > Dependent on the stability or the level of the supply ? > > > > You do know that the supply is also the full scale > > reference for the ADC, right ? (if setup that way). Is > > that what you mean with "dependent" ? > > > > Just guessing here... > > > > Jan-Erik. > > > > -- > > http://www.piclist.com hint: To leave the PICList > > mailto:piclist-unsubscribe-request@mitvma.mit.edu > > > > -- > http://www.piclist.com hint: To leave the PICList > mailto:piclist-unsubscribe-request@mitvma.mit.edu -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu