could the receiver be open collector output? You may need the pullup resistor.


---- Padu <padu@merlotti.com> wrote: 
> Gerhard Fiedler wrote:
> > Padu wrote:
> >
> >> I'm using CCP1 to measure the width of a pwm pulse generated by a RF
> >> receiver, the kind that is used in RC cars. The pwm is identical to the
> >> ones we use in RC servos. If I measure the signal amplitude, it goes
> >> from 0 to 4V, but as soon as I connect it to RC2, it drops to 0-2.9V
> >> range. Why is that? Will I have to use a voltage buffer to intervade the
> >> RF receiver and the CCP1 port? I'm using a PIC18F452.
> >
> > A buffer would only help if the problem is the max 1 uA that a PIC input
> > draws.
> >
> > I assume that RC2 is set to input (TRISC2=1), yes? :)  And that nothing
> > else is connected to RC2?
> 
> Correct
> 
> 
> > Does the voltage drop similarly if you connect a 3M or 4M resistor to the
> > receiver output? If not, connect Vdd through a 1k resistor to RC2 and
> > measure the voltage across the resistor. Should be less than 1 mV.
> 
> The interesting point is that if I pullup RC2 with a 10K it (measuring the 
> pwm) works. I'll perform the tests you suggested, but I was wondering what 
> I'm trying to do is something pretty common no? How people usually connect a 
> pwm source to be captured by the ccp module?
> 
> Padu
> 
> >
> > Gerhard
> > 
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