Also know's as a windspeed meter.
I use an harddrive motor as encoder. The bearings are very good.
Still working on it, but i tested the motor with the electronic's and that look's promissing.
The motor generate's 3 pulses per revolution. The motor consist of 3 winding's and generate's an
3 phase sinus on it's coil's.
I only use one coil which is measured with an comparator with feedback.
A oneshot is used to give pulses with a steady width so it's easy for an microcontroller to measure.
I used drain pipe end cap's to mount the motor and also to protect it against rain.
Violet trace: output from the motor
Blue trace: output from the comparator
Red trace: output from the Oneshot.