Wind Instruments
Measuring Air Speed

Hila Digital Anemometer

We designed this anemometer using a lawn sprinkler and ping-pong balls.  The signal to the computer is generated when a rotating flag interrupts the light falling on a photoresistor.

Any three bladed lawn sprinkler will do. Make sure it rotates freely.

Slice some ping-pong balls in half.  Attach the halves with short screws to the ends of the blades.
You may have to use some glue to secure the balls. (Super Glue works well)

Pull the base of the sprinkler to expose the rotating hub.
Cut a short dowel to slip into the hub.
(This example used a 1 cm dowel, 5 cm long)
The dowel should extend 2.5 cm past the base.
Attach a vinyl tape flag to the end of the dowel.
Flag: 1.5 cm long, 2 cm wide.

Insert dowel into hub.
Use Superglue to hold in place.
Be Careful: Superglue (CA) is dangerous!
Read safety instructions on container.

Build a base for the rotating assembly.
This base was constructed from 3/4" pine.
Outside dimensions: 10.5 cm X 14 cm.
Depth inside: 3 cm

Parts List (3/4" wood):
1 - 10.5 cm X 14 cm
2 - 3 cm X 6.5 cm
2 - 3 cm X 14 cm

Mount an LED and a Photoresistor as shown.
These electronic devices are mounted 1 cm off of center.

Dimensions vary with the size of the sprinkler.

The photoresistor is connected to pins 1 and 3 of the gameport.
(Link to more information about gameport connections)
The LED requires a 9 volt battery and a resistor (500 to 1000 Ohms)

The rotating assembly sits on the base.
Make sure the tape flag is the right length to interrupt the light flow to the photoresistor.

Use screws to hold the assembly together.
A black card may be needed to block external light from shining on the sensor.

This image shows the rotating flag blocking the light.
When no light shines on the photoresistor the computer joystick port senses a high resistance.

When wind blows causing the shaft to rotate,
light shines on the photoresistor, the computer joystick port senses a low resistance.

Use an Ohmeter connected to the photoresistor to test the operation of the anemometer. With the LED on, you should see the resistance changing significantly as you rotate the anemometer.

The joystick port on a computer is a useful port for connecting resistive devices like CdS cells (photoresistors).

Check out connecting to the joystick port: Hila Computer Engineering:Joystick port

Here is some Qbasic code to test your anemometer with
Enter this code into Qbasic, you should see the numbers bounce up and down as you rotate the shaft.




It is possible to create more sophisticated programs for your anemometer.

Here is one in Qbasic created at our camp, it displays a bar graph moving  with changing air speed: windoka.bas
When prompted, save the file to a folder. The program must be run in Qbasic.
This program worked well with a P3/700 MHZ computer. Different computers may require some change to the code.

It is possible to create a program in VB that will monitor the wind speed using this home made anemometer.
Check out the information on using the gameport with Visual Basic.
If you create an interesting program to monitor wind speed, please share it with us.

Project from Hila Science Camp