sample ----^^^^^-------- A/D uP pin
|
=
|
_____________________ Gnd
So it's actually a low pass filter. Which perforce, limits the response, but
you said your sampling time is > 1s, so it will be fine.
Just be aware that some cap technologies leak more than others, but it
should not be an issue.
Regards
Roland
On 6 February 2010 17:10, Steve Hodge <steve@terrafirma.us> wrote:
>
>
> Thanks. I assume put it in series between the input voltage and the uC ADC
> port pin? Steve
>
>
> | -----Original Message-----
> | From: AVR-Chat@yahoogroups.com <AVR-Chat%40yahoogroups.com> [mailto:
> AVR-Chat@yahoogroups.com <AVR-Chat%40yahoogroups.com>] On
> | Behalf Of Roland Jollivet
> | Sent: Saturday, February 06, 2010 1:07 AM
> | To: AVR-Chat@yahoogroups.com <AVR-Chat%40yahoogroups.com>
> | Subject: Re: [AVR-Chat] ADC source impedance
> |
> | Even if you have a source of 100K, put a small cap, 1uF, at the input
> | to the
> | ADC. It now becomes very low impedance to the ADC. (even 100n will be
> | fine)
> |
> | Time constant is 0.1s, so that's not aproblem. The biggest loss is the
> | charge/discharge of the cap if the signal varies a lot.
> |
> | Roland
> |
> |
> |
> | On 6 February 2010 00:32, Steve Hodge <steve@terrafirma.us<steve%40terrafirma.us>>
> wrote:
> |
> | >
> | >
> | > Thanks a lot for everyone's help. Sounds like I'm good to go. Steve
> | >
> | >
> | > From: AVR-Chat@yahoogroups.com <AVR-Chat%40yahoogroups.com> <AVR-Chat%
> 40yahoogroups.com> [mailto:
> | > AVR-Chat@yahoogroups.com <AVR-Chat%40yahoogroups.com> <AVR-Chat%
> 40yahoogroups.com>] On Behalf
>
> | > Of Jeff Blaine AC0C
> | > Sent: Friday, February 05, 2010 2:12 PM
> | >
> | > To: AVR-Chat@yahoogroups.com <AVR-Chat%40yahoogroups.com> <AVR-Chat%
> 40yahoogroups.com>
>
> | > Subject: Re: [AVR-Chat] ADC source impedance
> | >
> | > Steve,
> | >
> | > Yes, sorry for the error. 100k. There will be some finite upper range
> | to
> | > that due to leakage but it's got to me miniscule. But that's the
> | general
> | > idea. And if you are talking about sampling 1x/sec then the 20K
> | mentioned
> | > in
> | > the other message is not a problem at all. Good luck.
> | >
> | > Regards/Jeff
> | >
> | > From: Steve Hodge
> | > Sent: Friday, February 05, 2010 2:53 PM
> | > To: AVR-Chat@yahoogroups.com <AVR-Chat%40yahoogroups.com> <AVR-Chat%
> 40yahoogroups.com> <mailto:
> | > AVR-Chat%40yahoogroups.com <AVR-Chat%2540yahoogroups.com>>
>
> | > Subject: RE: [AVR-Chat] ADC source impedance
> | >
> | > Ah, got it. So it sounds like I'm just fine merely doubling it to 20
> | Kohms
> | > and only sampling once a second. I assume you intended to say "100k
> | > equivalent input"? Steve
> | >
> | > [Non-text portions of this message have been removed]
> | >
> | >
> | >
> |
> |
> | [Non-text portions of this message have been removed]
> |
> |
> |
> | ------------------------------------
> |
> | Yahoo! Groups Links
>
> |
> |
> |
> |
> | __________ Information from ESET Smart Security, version of virus
> | signature database 4841 (20100206) __________
>
> |
> | The message was checked by ESET Smart Security.
> |
> | http://www.eset.com
> |
>
> __________ Information from ESET Smart Security, version of virus signature
> database 4842 (20100206) __________
>
>
> The message was checked by ESET Smart Security.
>
> http://www.eset.com
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>
[Non-text portions of this message have been removed]