the outer disc is fixed.the rpm of the inner pin,spiining is variable.

i was thinking of using the count function,but if the osc is 20,then the pin would count the high every 4us.what if the rotation is 5us.

joe.
i will try your suggestion.

however! i would fancy only one rotation,and be able to work out te time taken for that rotation.

mackrackit.

what i am trying to do is to determine wind speed.hence the shaft spinning in the wind (hopefully),which will be the spindle in the bigger disc.