--- Thilo Klein <ostentativ@arcor.de> wrote:

> Hello.
> 
> I am using the ADC using Application note AN700
>
(http://ww1.microchip.com/downloads/en/AppNotes/00700a.pdf)
> with a
> 16F628.
> 
> I used the
>
http://www.sprut.de/electronic/pic/programm/compadc/compadc2.gif
> circuitry being similar to the one being included in
> the AN. The blue
> R3 is missing in my setup on purpose. "Eingang"
> means "voltage source
> to be measured". I changed R1, R2 and R3 to define a
> special area of
> voltage and a special value of voltage this area of
> voltage is to
> surround. So in my case the VS's value is changing
> from 0 to 5 volts.
> And the resistors force the ADC to subdivide 1,25 V
> to 4,56 V (into
> 1024 steps).
> 
> Unfortunately it works exactly the other way round.
> So values are
> measured between 0 and 1,25 V and 4,56 V and 5 V and
> not in between.
> 
  First you want to measure a range between 1.25 to
4.56? Okay. Why remove R3? It will latch the input to
high(Vdd) or low(Vss). From the diagram it is a
potential divider but in the AN700 it is not. Why do
you want this? Also check the output of the
comparator. You can inverse the output of the
comparator which might not be this case. 

John



 
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