I've a little project gone out which may require a cute hardware fiddle. It is battery powered. I have a pic, with the a/d reference one battery up (~1.5V), and the reference itself is only +1.2V above that whereas 2.0V is required as a minimum operating reference. As a bodge, I converted it to a 5V reference, but this affects battery life noticably. As the batteries get old they develop a higher impedance, and the voltage falls with the current requirements of the a/d conversion, screwing up my reference. I have to subtract the one batteryu up point, so more readings are required.
This 1.2V reference (MAX 6120EUR) is not pin compatible with anything I can lay hands on, and if I put in a bigger reference, I have an overhead problem anyhow. Another circuit onboard inverts this reference twice in making an adjustable low current powerr supply with reference to this 'one battery up' point. The opamp circuit offers these values: 1.2V(in) --> -0.6V(first stage) --> +0.8-1.2V (final stage). Now the question: If I modified to make the opamp circuit offer 1.2 --> -0.8 --> +0.8-1.2V, I could use from +1.2V to -0.8V (=2.0V)as a reference, and subtract the offset in software. I would then be having my vref- being generated by an opamp. Pinpoint accuracy aside (It's not required), does anyone see another fatal flaw with the above scheme? Specifically, If I take 2 readings one second apart, will they be similar? -- Regards, Declan Moriarty. -- Author: Declan Moriarty INET: [EMAIL PROTECTED] Fat City Network Services -- 858-538-5051 http://www.fatcity.com San Diego, California -- Mailing list and web hosting services --------------------------------------------------------------------- To REMOVE yourself from this mailing list, send an E-Mail message to: [EMAIL PROTECTED] (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB CHIPDIR-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing).
