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'[EE]: MCP3204 ADC Strange behaviour'
2002\10\01@125648 by vyas

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I am using MCP3204 in one the projects. It is a 12bit, 4 channel serial
interface ADC from Microchip.
According to datasheet, the maximum count (0x0FFF or 4096) is received when
input voltage is equal to Vref. Now my problem is that I get max count at
half Vref. I have applied 4.000 volt as Vref. I get max count at 2.0 volt.
But that is not all. The ADC again counts from 0000 to 4096 for 2.00 to 4.00
volts. I checked my circuit. I even applied simple DC voltage through 10K
pot. But the result is same.

I have also replaced the IC couple of times.

Has any one seen this problem? Any solution?

Vyas
web: http://www.sjvyas.com

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2002\10\01@171733 by vyas

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>Without further research, is this thing not set for bipolar V reading?

>/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/
>Wagner Lipnharski - UST Research Inc
>Orlando FLorida - USA - http://www.ustr.net
>/_/_/_/ Atmel AVR Consultant /_/_/_/

Nope, its a unipolar thing.

>What kind of serial interface?  Could it be a 13 bit ADC and you are
>ignoring the MSB?  That would be consistent with what you describe.  (never
>noticed a 13 bit ADC, though)

>--BobG

Again, nope, its a 12 bit ADC.


{Quote hidden}

Yes! I just don't know how I made that mistake and just didn't see it
even though I went through code few times. But now that you point it out, it
is glaring.

Thanks a lot.
Vyas

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2002\10\01@232906 by Bob Barr

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<re-sent to the list. Please change your reply-to address>

On Tue, 1 Oct 2002 21:23:14 +0530, wrote:

{Quote hidden}

If you re-check your code, you'll probably find that it's giving an
extra clock beyond what you expect. The symptoms of having 1
additional clock will match what you're seeing. And no, please don't
ask me how I know this. :=)


Regards, Bob

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2002\10\02@122840 by Peter L. Peres

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12bits + sign ? I do not know your part but I remember debugging problems
with a protocol that sent 10 bit ADC data with the sign in the last bit.
Then the codes would go 001 003 ... 3FF 000 002 004 ... 3FE took me a
while to understand.

Peter

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2002\10\03@114717 by Vyas

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Its just 12bits, no sign. The problem is solved with help from Wouter and
Bob.
I was giving one clock too many (13 instead of 12).

Vyas


> 12bits + sign ? I do not know your part but I remember debugging problems
> with a protocol that sent 10 bit ADC data with the sign in the last bit.
> Then the codes would go 001 003 ... 3FF 000 002 004 ... 3FE took me a
> while to understand.
>
> Peter

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