AVR-Chat

Steve,
How fast is the input signal varying and how often are you sampling?  If it's a slow signal you'll probably get away with it.

Tim Gilbert
JEM Innovation Inc.
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  ----- Original Message ----- 
  From: Steve Hodge 
  To: AVR-Chat@yahoogroups.com 
  Sent: Friday, February 05, 2010 1:35 PM
  Subject: RE: [AVR-Chat] ADC source impedance


    
  I didn't give enough information. The particular application does not need
  the full 10 bits of resolution. 9 bits or even 8 bits would be ok. I'm
  trying to keep the board to minimal size so I'd prefer not to have to cram
  in an opamp. In addition, the application will allow things to be
  calibrated, so a correction could be applied in software. Anyone have a gut
  feeling given all that? That's all I'm looking for. Steve

  From: AVR-Chat@yahoogroups.com [mailto:AVR-Chat@yahoogroups.com] On Behalf
  Of David VanHorn
  Sent: Friday, February 05, 2010 12:22 PM
  To: AVR-Chat@yahoogroups.com
  Subject: Re: [AVR-Chat] ADC source impedance

  On Fri, Feb 5, 2010 at 12:37 PM, Steve Hodge <steve@terrafirma.us
  <mailto:steve%40terrafirma.us> > wrote:
  > The Atmel data sheets, at least the ones I'm dealing with, say the "ADC is
  > optimized for analog signals with an output impedance of approximately 10
  K
  > or less". Does anyone have any experience about how much you can exceed
  > this 10 K?

  Depends on how much precision you want to loose, and there are no hard
  answers.
  A buffer amp will let you have >1Gohm, and there are some flea-powered
  opamps out there.

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