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Re: [avr-gcc-list] Troubles with ADC on ATMega16

From: Keith Gudger
Subject: Re: [avr-gcc-list] Troubles with ADC on ATMega16
Date: Thu, 8 May 2003 15:56:53 -0700 (PDT)

You call "a 50k pot" low input impedance?  That was about the value I
needed 30 us to be able to read.  Remember that the delay needed is
*between* switching the mux and starting the A/D conversion.


On Thu, 8 May 2003, Larry Barello wrote:

> I don't wait at all, but I do make sure I have fairly low input
> impedance.  Either a 50k pot (for variable user input) or put a .1uf
> capacitor to filter the input signal.  I am never chasing high speed
> signals so I just jammed a large capacitor to clean things up.  If I
> were trying to do high speed conversion I would use a low offset
> buffer to drive the inputs.  If the lines are floating, each channel
> will tend to report the same value as the last driven channel - it is
> pretty sensitive.
> Cheers!
> ----- Original Message -----
> From: "Keith Gudger" <address@hidden>
> > I have found that I must wait about 30 us after switching the A/D
> input
> > channel before starting the A/D converter.  This allows the input to
> > settle down.  It all depends on your inputs - how much capacitance
> and
> > resitance do they have?
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