Problems with ADC0838

Archiver

Hi all,

We are trying to use the ADC0838 to read voltage from a pressure to
voltage sensor. The pressure to voltage sensor is made with two
pieces of polish copper, we solder connection wires to each board and
between both boards we have a conductive anti-static foam- we found
this example in one of the engineer's mini notebook by Forrest Mims.

We are succesfully reading the voltage variation using the ADC0831,
but we need to read from 8 pressure to voltage sensors. We decide to
use the ADC0838 and connect one sensor to each chanel. So far, when
we connect only one sensor to only one of the channels, we are able
to read the voltage from that channel, but the problem is that we are
getting funny numbers in the other channels, when we should be
getting zero. It is not constant, sometimes we get zero and others we
get a weird number. It doesn't have any predictable pattern. The code
that we are using to read the ADC0838 was taken from:

http://www.hth.com/filelibrary/BS2-IC/
file name: ADC0838.zip

Does anyone in this list have experienced the same problem? or does
anyone have an idea why this is happenning? or how to avoid it??

thanks
Marilenis Olivera

Archiver

I have found that when an input port (at least on the Stamp BS2 I have) is
not grounded through a resistor to "draw off" any voltage that may exist at
the port, the port may do funny things. I found a 10K ohm resistor fine
which seems to create a ground reference for the port when left floating.
Care must be taken with your input signal as the 10K may wind up dividing
the input signal. The value will depend on what you're doing.

Worked for me

Jay

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Original Message

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From: <mari_olivera@h...>
To: <basicstamps@egroups.com>
Sent: Saturday, November 04, 2000 9:53 PM
Subject: [noparse][[/noparse]basicstamps] Problems with ADC0838


> Hi all,
>
> We are trying to use the ADC0838 to read voltage from a pressure to
> voltage sensor. The pressure to voltage sensor is made with two
> pieces of polish copper, we solder connection wires to each board and
> between both boards we have a conductive anti-static foam- we found
> this example in one of the engineer's mini notebook by Forrest Mims.
>
> We are succesfully reading the voltage variation using the ADC0831,
> but we need to read from 8 pressure to voltage sensors. We decide to
> use the ADC0838 and connect one sensor to each chanel. So far, when
> we connect only one sensor to only one of the channels, we are able
> to read the voltage from that channel, but the problem is that we are
> getting funny numbers in the other channels, when we should be
> getting zero. It is not constant, sometimes we get zero and others we
> get a weird number. It doesn't have any predictable pattern. The code
> that we are using to read the ADC0838 was taken from:
>
> http://www.hth.com/filelibrary/BS2-IC/
> file name: ADC0838.zip
>
> Does anyone in this list have experienced the same problem? or does
> anyone have an idea why this is happenning? or how to avoid it??
>
> thanks
> Marilenis Olivera
>
>
>
>
>
>
>