An anemometer spins when pushed by the wind. The rate of this spin is a function of the wind’s speed. The spin rate can be sensed in a variety of ways:

• couple the spinner to a generator and measure the voltage or current produced,
• have the spinner interrupt a light beam and count the period of each revolution
• attach a permanent magnet to the spinner and sense the passage of the magnet with a magnetic reed switch or Hall-effect device.

Using a microcontroller, the simplest technique is to to measure the spinner’s time period of revolution and use a model of the spinner’s characteristic behavior to estimate the wind speed.