Now, theres probably a hundred different ways of doing this, as have been proven by all the posts. Just thought I'd mention how I've done it in the past; Just by measuring time between each falling or rising edge of your frequency input. I managed to get spot on accuracy using this method in the rage of approx. 800Hz to 4kHz. (Dividing the signal by two before it reached the controller). I did it just by starting a timer on one edge, stopping it on the next and calculating the frequency from the resulting time. (1/time)... The only drawback with this approach is that if you measure every pulse you get in with this method it is going to hog a lot of your processor time when you reach the higher frequency, so it might be a good idea to gate the incoming signal in some way. Perhaps by just using and and gate or something similar...

For all the people that have read my other post about my rev counter; sorry for the repeat....

Just my 0.02NOK...

Øyvind..