This is my homemade digital anemometer. It is made of cups rotating with a magnet triggering a reed switch. The wires are connected to an Arduino Uno that calculates the time between consecutive pulses (after reed switch debouncing by my arduino software)
This is an experiment to see if barometric pressure and its time derivative can be correlated with weather conditions for up to 12 hours . Data is from Dark Sky relayed through an ESP8266 running Arduino code. Weather is in Centreville, Virginia.