"David E. Olson" wrote:
>
> Tony - I should have pinged you earlier - I knew you were working on
> something like this.
>
> OK. You're basically doing period counting rather than explicit pulse
> counting, which should be analogous.
>
> It certainly reduces the number of interrupts out there.
>
> > ; Interrupt routine may capture many speed values,
> > ; but the capture registers are only read every 500mS
> > ; for a display update.
>
> I'm not sure where you're reading the capture registers every 500ms. Your
> ISR seems to be CCP related and not TMR related.

In the main code loop, one of it's tasks is to read the capture
registers every 500mS or so. The main loop time is controlled by TMR0
for a 50mS loop time. I count 10 of these loops, and then call SpeedCal
to update the speed display. In my case it is displayed on a virtual
headset via a 2.4GHz video link. Thus I can see where the vehicle is
heading, and the speed at the same time.

> If that's the case, then
> your ISR is firing on every falling edge.

Yes, but the capture registers are overwritten continuously, but mostly
discarded, and TMR1 is reset as well so I can get the next capture. It
works well so far from a sig gen.

I got a 5V opto schmitt trigger device ($5 from RS) that 'looks' through
the slots cut into the wheel rims. I get a nice square wave which is fed
direct to pin RC2 with a pullup resistor.

--
Best regards

Tony

http://www.picnpoke.com
mailto:sales@picnpoke.com