On Sun, 1 Sep 2002, Lars Th=F6rnqvist wrote:

> I=92m trying to measure a frequency created from an RC oscillator using=
 a
> 16F877. My problem is that my program takes to long to "find" the
> frequency, and it never stabilizes even though the input signal is
> constant.

How fast does it need to find the frequency?  And how are you trying to d=
o
it now?

> Have anyone done this before using CCS or any other C-compiler?
>
> Any idea how to do this? Right now I=92m trying to calculate amount of
> interrupts I get during a specified time period (Using built in
> timer)... but as I said... It never stabilizes well enough.

I have done this as part of a project in which I needed to determine the
speed of a rotating motor by the output of a tachometer-like device.  I
used the tach pulses as input to CCP1 and used the CCP1 interrupt to read
TIMER1 to get the period between pulses.  I then used a software filter t=
o
smooth and stabilize the readings:

#int_CCP1
void CCP1_int() {
    set_timer1(0);
    accumulator -=3D accumulator/8;
    accumulator +=3D CCP_1/8;
}

Hope this helps.

Dale

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