gnupic: ADC using an RC circuit instead of a ADC port??
Subject:
Re: ADC using an RC circuit instead of a ADC port??
From:
"RAY MCDONALD" ####@####.####
Date:
31 Aug 2002 01:00:42 -0000
Message-Id: <001c01c25089$c361bfa0$03824b0c@RayMcDonald>
From: "Ray McDonald" ####@####.####
To: "Martin Peach" ####@####.#### ####@####.####
Subject: Re: ADC using an RC circuit instead of a ADC port??
Be careful making measurements with a simple RC circuit. You are measuring
a relatively quick signal with variation that will confound your A/D
readings. The
RC circuit is a non linear (exponential) type of integrator and I would
expect you would like a rather quick
instantaneous type reading which may need synchronization with the engine
RPM and crankshaft timing.
I believe that I would use an external A/D with an included sample/hold
function which could be strobed
when each measurement was needed. Depending on the required A/D resolution,
you may be able to use a serial
interface or if bandwidth is a problem then a parallel data out unit would
be needed.
Hope this helps
Ray McDonald
----- Original Message -----
From: "Brent Picasso" ####@####.####
To: "Martin Peach" ####@####.#### ####@####.####
Sent: Friday, August 30, 2002 5:40 PM
Subject: Re: ADC using an RC circuit instead of a ADC port??
> Thanks for the great replies..
>
> When you say "low speed input" - what's low speed? do
> you think I could take a measurement within 2ms?
>
> I want to track a pressure sensor to track changes in
> a automobile's manifold pressure.
>
> I want to measure it at for at least every ignition on
> the engine... at 10,000 RPM with a 4 cylinder engine
> that happens every 4ms or so.
>
> Any ideas on a 16F628 + ADC equivalent PIC I could
> use?
>
>
> Thanks,
> Brent
>
> --- Martin Peach ####@####.#### wrote:
> > Brent Picasso wrote:
> > >
> > > Not sure if I saw it on this mailing list before,
> > but
> > > I'm trying to determine if it's feasable to do
> > > analog-digital conversion using a RC delay using
> > > standard IO pins, and a counting routine in the
> > > software.
> > >
> > > I've searched google; didn't find anything good.
> > >
> > > I'd like to use a 16F628 for my project as I only
> > need
> > > one ADC line!
> > >
> > > thanks in advance for any help.
> > > Brent
> > There's an app note about that on the microchip web
> > site, using a
> > 12c50X:
> >
> >
> http://www.microchip.com/download/appnote/devspec/16c5x/00513d.pdf
> >
> > It works fine for low speed inputs like temperature
> > or potentiometer.
> > /\/\Martin
> >
> >
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