MAX195

[Gerhard Glatte]

Hello Newsgroup,

my name is Gerry and I currently work with a group on our diploma project
(that's the final exam period of my school type). In this project we use the
MAX195 16bit analogue digital converter.

We have now the following problem:
We made a printed circuit board and control the MAX195 directly with a PIC
microcontroller (PIC16F877). The MAX195 converts the analogue signal
correctly, but nearly every 3 seconds (it seems to be a periodic process)
the converted voltage "jumps"(e.g. from 1,12568 to 1,13568), but the
analogue signal (which has to be converted) does not.

We clock out the data serially (after the conversion) by setting the SCLK
pin high and low (controlled by the microcontroller).

If anyone of you has experiences with this ADC please help us,
we are trying to solve that problem for weeks without any results,

Gerry

 

[Marco]

Gerhard Glatte wrote:

Hello Newsgroup,

my name is Gerry and I currently work with a group on our diploma project
(that's the final exam period of my school type). In this project we use the
MAX195 16bit analogue digital converter.

We have now the following problem:
We made a printed circuit board and control the MAX195 directly with a PIC
microcontroller (PIC16F877). The MAX195 converts the analogue signal
correctly, but nearly every 3 seconds (it seems to be a periodic process)
the converted voltage "jumps"(e.g. from 1,12568 to 1,13568), but the
analogue signal (which has to be converted) does not.

We clock out the data serially (after the conversion) by setting the SCLK
pin high and low (controlled by the microcontroller).

If anyone of you has experiences with this ADC please help us,
we are trying to solve that problem for weeks without any results,

Gerry

Test

 

[Marco]

Gerhard Glatte wrote:

Hello Newsgroup,

my name is Gerry and I currently work with a group on our diploma project
(that's the final exam period of my school type). In this project we use the
MAX195 16bit analogue digital converter.

We have now the following problem:
We made a printed circuit board and control the MAX195 directly with a PIC
microcontroller (PIC16F877). The MAX195 converts the analogue signal
correctly, but nearly every 3 seconds (it seems to be a periodic process)
the converted voltage "jumps"(e.g. from 1,12568 to 1,13568), but the
analogue signal (which has to be converted) does not.

We clock out the data serially (after the conversion) by setting the SCLK
pin high and low (controlled by the microcontroller).

If anyone of you has experiences with this ADC please help us,
we are trying to solve that problem for weeks without any results,

Gerry

Hi

You'll probably have a timing failure.

Datasheet:
The data bits can be read either during the conversion, at the
CLK clock rate, or between conversions asynchronous with CLK at the SCLK
rate (up to 5Mbps).
/Datasheet

Do you monitor EOC?

Do you use TRACK/HOLD?

Is it possible you do a dataread during calibration?

Any noise on the power supply lines?

Quite some possibilities to mess up a measurement... Sorry I don't have
an out-of-the-box solution for you...

 

[JW]

On Wed, 25 Feb 2004 20:09:20 +0100 "Gerhard Glatte"
<gerhard.glatte@world4you.com> wrote in Message id:
<c1irvj$sal$1@newsreader1.utanet.at>:

Hello Newsgroup,

my name is Gerry and I currently work with a group on our diploma project
(that's the final exam period of my school type). In this project we use the
MAX195 16bit analogue digital converter.

We have now the following problem:
We made a printed circuit board and control the MAX195 directly with a PIC
microcontroller (PIC16F877). The MAX195 converts the analogue signal
correctly, but nearly every 3 seconds (it seems to be a periodic process)
the converted voltage "jumps"(e.g. from 1,12568 to 1,13568), but the
analogue signal (which has to be converted) does not.

Due to the fact that the incorrect result is off by only one bit, as a
guess, I'd say that either your clock is not properly synchronized to
your data (Try shifting the clock a bit) or your design has a dropout on
the serial clock - because it seems to occur on a regular basis, perhaps
the PIC is busy running some subroutine or something?