I don't believe it is worth to add a op to divide V for ADC acting as a load! I think ADC as a fixed input Z load! Simple 100K 10 turn pot as divider, has below part parallel with ADC's Z, it will give accurate enough V dividing! By adding a op, you add error as well! And I believe, this error is not smaller than above, where simplifying ADC as a pure R. ----- Original Message ----- From: "Jinx" To: "Microcontroller discussion list - Public." Sent: Monday, November 14, 2005 8:58 PM Subject: Re: [PIC] How to read Battery voltage with PIC > > can't connect the 12V battery into the A2D of the PIC > > Use a high-value (100s of k or megohms) resistive divider > into a high-Z input, low-power op-amp (eg TLC271, 10uA > operating) to give you the drive for the A2D. Op-amp Vcc > is from a PIC pin so it can be turned off to minimise drain > > Could even use a FET / transistor to disconnect the divider too > > However, as the regulator is a hungry hungry hippo 7805 > (Iref ~ 5mA), a few 10s of uA isn't really going to make that > much difference, so you could go with a lower-R divider, > just enough to meet the A2D input Z > > Different if you wanted as complete a power-down as possible, > then you'd be looking at regulator power management too > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist