At 11:10 PM 5/15/2005 +0200, you wrote:
>Spehro,
>
>First of all thanks for noticing  the +/. swap. Had it on paper and the 
>component in eagle was the other way.  Probably should have taken me 
>several hours to find on a board... ;-(
>
>When you say adding a 2nd pole filter do you mean to replace the PWM 
>LPF?  My thought was to also remove ripple in software. In this case it 
>has known properties so this should be possible.

If it's large you can run into nonlinearities when you don't expect to.

>Where does the 11.8 come from in 100/11.8?

In the DC path, the 1.8K is in series with the 10K (think of the capacitor
as being open circuit for DC). If you put a buffer in there,
as I suggested, it will reduce that to zero and eliminate the effect of the
PIC port output impedance.

That's the gain looking from a fictional DC PWM source. The gain from the
sensor will be half of (that number plus 1) because of the  voltage divider
on the non-inverting input.


Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
 >>>Inexpensive test equipment & parts http://search.ebay.com/_W0QQsassZspeff


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