On Mon, 18 Jun 2007 15:44:07 -0600 (MDT) you wrote: >Most microcontroller's ADC will not like a 10M load, the charge time will >be very high and not very accurate. I have used a low power OpAmp to run >very high Z dividers into and the output of the OpAmp is nicely low Z for >that ADC to be happy with. Its a few more pins and passive parts than the >FET but the readings tend to be more repeatable. > >DLC It isn't 10M if a cap is across it! >> On Mon, 18 Jun 2007 13:02:17 -0400 you wrote: >> >>>I think you need to disconnect the voltage divider using an fet. The >>> voltage divider will draw more juice than the avr in sleep mode! I assume >>> you read the datasheet about the half dozen or so best ways to cut down >>> on power consumption? (turn off a/d, turn off pullups, which sleep mode >>> to use, etc) >>> >> >> Forget the FET. 10M resistors are cheaper if the consumption is that >> critical. >> The only buffer needed is a 0.1uF cap. >> -- Ralph Hilton http://www.ralphhilton.org C-Meter: http://www.cmeter.org FZAOINT http://www.fzaoint.net
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Re: [AVR-Chat] Using the ADC to measure the battery supply?
2007-06-19 by Ralph Hilton