We had a discussion regarding this in a prior thread, and I thought I the capacitor trick would work great. Unfortunately, I was shot down by those who noted that the inpuit leakage current on the pin was specified such that it would bias the input with such high resistances. Bob Ammerman RAm Systems ----- Original Message ----- From: "Gerhard Fiedler" To: Sent: Tuesday, November 13, 2001 3:39 PM Subject: Re: [PIC]: Lowest power consumption > At 18:08 11/13/2001 -0500, Eoin Ross wrote: > >One question about the data sheet for a 12C671 - it says I need to (on pg > >48) keep impedance at or below 10k on the analog inputs - I want to use a > >2M/1M resistor divider to drop the input to 3V or less (Will be using a 3V > >low current reg for the PIC) It looks like I would be breaking that rule > >with using a 1M impedance ?? > > That's correct. But you can put a capacitor to ground between your divider > and the PIC input. The size depends on your requirements: the bigger, the > more precise and the slower. From ~15n on the error is below 1 bit. The cap > divides its charge with the internal capacitances, thus creating something > like a virtual low-impedance voltage source (if it's big enough). Of course > it will create a low pass with your divider, but for battery sensing this > shouldn't matter. > > ge > > -- > http://www.piclist.com hint: PICList Posts must start with ONE topic: > [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads > > -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads