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<p>Regarding unstable ADCs with PWM signals ...</p>
<p>I'm sure you've already done this, but "just in case":</p>
<p>Take your first ADC reading and discard it.</p>
<p>Take an odd number of sequential ADC readings, adding them
together. When done, divide by the ODD number you measured</p>
<p> Read ADC and Discard <br>
</p>
<p> Read 9 ADC values, and add them together (x=x+ADCValue)</p>
<p> x/9 = 9-averaged ADC Value.</p>
<p><br>
</p>
<p>The purpose of discarding the first ADC value is the ADC will
have some random value held by the input capacitor. When you read,
this voltage gets pulled to zero, ready for the next ADC read. <br>
</p>
<p>I always have deleted the first ADC value, and run an odd-number
average with ADCs. This worked very well in an industrial, very
high current environment (measuring 1000 - 1600 Amps in under 100
mS). <br>
</p>
<p>If you've already implemented this, you will want to include a
low pass filter with the 3dB point 1/t of your measurement period.
There is no reason to have a higher frequency than this, and a
lower frequency filtering will cause your ADC values to lag actual
values.</p>
<p>Also, be careful of high crest values (sharp peaks and dips) ...
NEVER assume your ADC input is a pretty sine wave or a SLOWLY
changing DC voltage/current. <br>
</p>
<p>This work was performed on an Isopod Microcontroller board (New
Micros, no longer in business) <span style="left: 513.8px; top:
1245.92px; font-size: 16.7px; font-family: serif; transform:
scaleX(1.00201);">using a Motorola DSP56F800 series 16-bit
Digital Signal Process (DSP) processor running at around 80 MHz.</span></p>
<p>Yea, that long ago!</p>
<p>Hope this helps.</p>
<p>Regards,</p>
<p>Rick<br>
</p>
<p><br>
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