The main problem on any displayed value, the human must be able to read it out !

Thus for practical usage an update rate not faster as 2..5 readings per second was optimal.

To do so I use on my frequency meter the following approach:

I count all periods (revolutions) for minimal 500msec. then I detect the final time, if exact the next period (revolution) was finished.

Thus I have the whole time for exact n periods.

And with the formula:

f = f(crystal) * number of periods / time value / 12

I get the result.

For you to get the revolutions per minute simple multiply this formula * 60.



Peter