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
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.
9484 Chesapeake Dr.
San Diego, CA 92123
(858) 571-1226 fax
----- Original Message -----
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 ?
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