ARRGH ! ADC problem ..

Archiver

So I rise to the surface once again, but only because I am in trouble
[noparse]:([/noparse] I've hooked up an ADC to a Basic stamp. All the connections seem to
be ok and I'm just using the demo program that came with the LTC1298 (this
is an LTC1298 BTW).

The output just waves around all over the place but seem to regularly be
1024 2048 etc ... A test meter on the input pin say's it's stable at 2.5V
(the other is bound to the ground). Power supply is stable, ground is OK.

Any possible idea what could be wrong ?

Justin Pentecost Focus Puller -London
Tel:- 01491 826759 Fax:-01491 826655
justin@k...
CML Listpig

Archiver

Its most likely noisy power. A multimeter is not going to be able to show
the voltage deviations. They're designed to show a steady voltage since we
all know that voltages are rarely actually steady. You'd need an ocilliscope
to see the variations.

Take a look at this message and others in its thread. Quite a few pointers:
http://groups.yahoo.com/group/basicstamps/message/26420

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Original Message

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From: "Justin Pentecost" <justin@k...>
To: <basicstamps@yahoogroups.com>
Sent: Monday, December 09, 2002 1:41 PM
Subject: [noparse][[/noparse]basicstamps] ARRGH ! ADC problem ..


> So I rise to the surface once again, but only because I am in trouble
> [noparse]:([/noparse] I've hooked up an ADC to a Basic stamp. All the connections seem
to
> be ok and I'm just using the demo program that came with the LTC1298 (this
> is an LTC1298 BTW).
>
> The output just waves around all over the place but seem to regularly be
> 1024 2048 etc ... A test meter on the input pin say's it's stable at 2.5V
> (the other is bound to the ground). Power supply is stable, ground is
OK.
>
> Any possible idea what could be wrong ?
>
> Justin Pentecost Focus Puller -London
> Tel:- 01491 826759 Fax:-01491 826655
> justin@k...
> CML Listpig
>
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
> from the same email address that you subscribed. Text in the Subject and
Body of the message will be ignored.
>
>
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
>
>

Archiver

Justin,

What is your setup? What is providing input voltage, and what is providing
the ref voltage (VDD) to the LTC1298? I am using a LTC1298, and get
variations of about +/- 1-2, sometimes as high as 3. This is only using a
LM7805 as a regulator, better results can be had with a precision regulator.
Which I may switch to in my application because I have one, not because I
really need it. Do you have a cap across the power supply of the LTC1298?

Jonathan Peakall

www.madlabs.info

---

Original Message

---

From: "Justin Pentecost" <justin@k...>
To: <basicstamps@yahoogroups.com>
Sent: Monday, December 09, 2002 1:41 PM
Subject: [noparse][[/noparse]basicstamps] ARRGH ! ADC problem ..


> So I rise to the surface once again, but only because I am in trouble
> [noparse]:([/noparse] I've hooked up an ADC to a Basic stamp. All the connections seem
to
> be ok and I'm just using the demo program that came with the LTC1298 (this
> is an LTC1298 BTW).
>
> The output just waves around all over the place but seem to regularly be
> 1024 2048 etc ... A test meter on the input pin say's it's stable at 2.5V
> (the other is bound to the ground). Power supply is stable, ground is
OK.
>
> Any possible idea what could be wrong ?
>
> Justin Pentecost Focus Puller -London
> Tel:- 01491 826759 Fax:-01491 826655
> justin@k...
> CML Listpig
>
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
> from the same email address that you subscribed. Text in the Subject and
Body of the message will be ignored.
>
>
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
>
>
>
>