Forums

ADC signal noise in EVB

Started by Unknown October 25, 2002
Hi All,
I have tried to use ADC in DSP56F805 EVM with SDK application note "ADC"
and I have modified it to view result of conversion with PC-MASTER. I have
connected a potentiometer to drive AN1 in J9 (A/D connector) but the result
is that the readed value has an oscillation range of 40 bits. After, I
tried to connect a 3.6V battery with a divider resistor network by 2 and
the result has been the same. Is this high signal noise normal? How can I
reduce the noise to obtain a good value read ?

Thanks
--------\
--------

Marco Pellizzaro
QEM srl
S.S. 11 Km 339 LocalitSignolo
36054 Montebello Vic.no - VI - ITALY
Phone +39-0444-440061 Fax. +39-0444-440229
e-mail:
http://www.qem.it
--------\
--------




We had the same problem here, and we use a digital filtering algorithm on the
analog input data. Real-world analog input signals from sensors generally
require some amount of filtering anyway, to get a usable signal. Please see the
attached file, which has the digital filtering algorithm we use here. This
algorithm is used by many vendors of analog input modules, and is (in my
experience) a "de-facto" industry standard.

The comment at the beginning of the function "Set_Ain_Filter_Values()" describes
the digital filtering algorithm in some detail. Please note that this file is
made up of pieces copied from several library files here, and is NOT intended to
be compiled. Also note that most of the data structures are placed in P RAM in
our applications, so we need to use functions like "memReadP16()" and
"memCopyPtoX()" to access the data.

I hope you find this information useful.

Regards,

Art Johnson
Senior Systems Analyst
PMC Prime Mover Controls Inc.
3600 Gilmore Way
Burnaby, B.C., Canada
V5G 4R8
Phone: 604 433-4644
FAX: 604 433-5570
Email:
http://www.pmc-controls.com
-----Original Message-----
From: [mailto:]
Sent: Friday, October 25, 2002 1:44 AM
To:
Subject: [motoroladsp] ADC signal noise in EVB Hi All,
I have tried to use ADC in DSP56F805 EVM with SDK application note "ADC"
and I have modified it to view result of conversion with PC-MASTER. I have
connected a potentiometer to drive AN1 in J9 (A/D connector) but the result
is that the readed value has an oscillation range of 40 bits. After, I
tried to connect a 3.6V battery with a divider resistor network by 2 and
the result has been the same. Is this high signal noise normal? How can I
reduce the noise to obtain a good value read ?

Thanks
--------\
--------

Marco Pellizzaro
QEM srl
S.S. 11 Km 339 LocalitSignolo
36054 Montebello Vic.no - VI - ITALY
Phone +39-0444-440061 Fax. +39-0444-440229
e-mail:
http://www.qem.it
--------\
-------- _____________________________________
Note: If you do a simple "reply" with your email client, only the author of this
message will receive your answer. You need to do a "reply all" if you want your
answer to be distributed to the entire group.

_____________________________________
About this discussion group:

To Join:

To Post:

To Leave:

Archives: http://www.yahoogroups.com/group/motoroladsp

More Groups: http://www.dsprelated.com/groups.php3 ">http://docs.yahoo.com/info/terms/



Attachment (not stored)
ADCfilt.zip
Type: application/x-zip-compressed

I am not using the EVM, but I have designed the 803 into a temperature
controller. I am using all 8 A/D channels to read RTD inputs. Consecutive
readings typically within +/- 1 count.

On your EVM, are you using the ADref to power the potentiometer? If not, any
variations in the power supplies will affect your A/D result. When you testing
using the battery, if the ADref power supply is fluctuating, you will get noisy
A/D results.

The three LSB's of the AD result registers are always zero. Is the result shown
by PC_MASTER right shifted so that you only get 12 bits? If not, your readings
may really only be bouncing by 5 counts.

On other projects, I often use an Olympic or median window filter. Each cycles,
I take one new sample plus the preivoud five, throw out the highest and lowest
of the six, and average the remaining four. Ending up with 4 (or 8) samples
makes the math faster on most processors. This filter works well when popcorn
noise causes an occasional wild reading in an otherwise stable signal.

Sheldon Black
RiboTech, Inc.
9484 Chesapeake Dr.
Suite #807
San Diego, CA 92123
(858) 571-1235
(858) 571-1226 fax

----- Original Message -----
From:
To:
Sent: Friday, October 25, 2002 1:43 AM
Subject: [motoroladsp] ADC signal noise in EVB Hi All,
I have tried to use ADC in DSP56F805 EVM with SDK application note "ADC"
and I have modified it to view result of conversion with PC-MASTER. I have
connected a potentiometer to drive AN1 in J9 (A/D connector) but the result
is that the readed value has an oscillation range of 40 bits. After, I
tried to connect a 3.6V battery with a divider resistor network by 2 and
the result has been the same. Is this high signal noise normal? How can I
reduce the noise to obtain a good value read ?

Thanks

--------\
--------

Marco Pellizzaro
QEM srl
S.S. 11 Km 339 LocalitSignolo
36054 Montebello Vic.no - VI - ITALY
Phone +39-0444-440061 Fax. +39-0444-440229
e-mail:
http://www.qem.it

--------\
--------
_____________________________________
Note: If you do a simple "reply" with your email client, only the author of
this message will receive your answer. You need to do a "reply all" if you want
your answer to be distributed to the entire group.

_____________________________________
About this discussion group:

To Join:

To Post:

To Leave:

Archives: http://www.yahoogroups.com/group/motoroladsp

More Groups: http://www.dsprelated.com/groups.php3