The are a few ways to measure wind speed, some involving ultrasound transducers, some based on cooling effect of air flow but most common technique uses spinning cups and measures their rotation speed. There are also a few ways to measure this rotation, some using a dynamo, some using Hall sensors but most use a photo-interrupter in a way much like it’s found in a computer mouse for example.
This kind of anemometer is presented in this project. Four hemispherical cups are attached to a rotating axis. At the other end of the axis there is a disc with 4 slits. Holes can also be used if they’re close enough to the edge. This disc’s slits or holes go in the photo-interrupter gap. Now when wind blows in the cups and spins the axis, the photo-interrupter will output a series of pulses whose period depends on the speed of rotation. Now you can either measure frequency, number of pulses within a time unit or the mean voltage of these pulses.
Note that the greater number the whole or slits are done in the disc the greater the resolution will be. The diameter of the disc is also an important factor in resolution.
The rotation speed is measured in this project by a PIC16F873 microcontroller. The photo-transistor has its collector connected to Port A0 from the PIC. The developer of the project is planning to display the measurement result on a screen but he also made an USB interface to send the data to PC. USBN9604 IC is used for this task. The article recommends that you ground the parallel input pins if not used so that it won’t cause interference.
The project right now is a work in progress but the principles of its operation have been stated. Also a schematic is provided and the circuit explanation. I for one, am waiting for complete article to check out the measurement algorithm.
Measuring Wind Speed: [Link]