AVR-Chat

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.

>-----Original Message-----
>From: Richard Cooke <rcooke@digitalwavelength.com>
>To: AVR-Chat@yahoogroups.com
>Sent: Mon, 18 Jun 2007 12:30 pm
>Subject: [AVR-Chat] Using the ADC to measure the battery supply?
>
>
>
>Hi Folks,
>
>I'm using the ATmega48V in a project and I need to monitor the battery
>level (2 AAA cells) every so often and when low give an indication to
>the user that it's time to change them.
>
>I'm trying to minimize current consumption and I'm using the internal
>1.1V reference so I'm using a voltage divider 1M + 3M to bring the
>signal down to below the 1.1V reference.  I don't care how long the
>conversion takes as I'm only making the measurement every 10 minutes
>or so.
>
>Do I need to use a buffer between the divider and the input to the
>ADC?  If I do, what small, cheap and low power chip would you recommend?
>
>Thanks,
>
>Richard Cooke

--
Ralph Hilton
http://www.ralphhilton.org
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