Michael Rigby-Jones wrote:
> The period of just one
> tooth on the 16 tooth wheel at 200RPM would be a whopping 188ms,

This is WAY off, observe:

(200rev/min / 60sec/min) = 3.333Hz shaft speed

3.333Hz * 16 teeth/rev = 53.33Hz tooth frequency

1 / 53.33Hz = 18.8mS tooth period

> so you
> wouldn't need to poll the inputs particularly quickly to get a
> reasonable precision.

Except that this is based on a value that is off by an order of magnitude.

> (the CCP module is great for arbitrary rate interrupts
> with no timer loading overhead)

Yes, a CCP module can be used to generate a periodic interrupt.  However,
my first choice for this is timer 2 since it's less useful for other
stuff.

> By running a counter for each
> input and storing the value on a rising (or falling) edge you can
> easily and quickly make a multi channel counter.

But he wants speed, not total elapsed revolutions.


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