Noam Dotan has published this from CometME in Palestine:
Counting the turns may be confusing especially if you need to wind some 260 turns per coil. A simple counter is based on low cost calculator where the ‘=’ key is wired through a magnetic switch (like the one on a bicycle speedometer) and all you have to do is key in :1 + =. each time the switch is activated by the magnet in each revolution, the ‘=’ key is ‘pressed’ and the number increased by
Very cool, and the price is right. I did that using a photo-transistor as the switch. Later, i graduated to a little digital counter ($10CAN) that I picked up at Radio Shack. For that one, i used an emitter-detector pair which is very easy to use. You simply draw a dark line on your rotating form, making sure that the background is a light colour…or vice versa. Then, the counter will increase each time the line passes. Oh yea, for that one i wired in a 9 volt battery to power the emitter-detector since there isn’t an internal voltage supply for the trigger circuit….pick a suitable resistor to keep within the specs of the e-d pair.