Build a wind gauge

A magnet on a sensor provides wind speed information

Author: Jonathan Filippi, Prato, Italy, [email protected]

Online since: 10/06/2010, Number of visits: 90026

For the non-contact Hall effect sensor in my homemade anemometer (wind gauge), I needed a shaft that could provide the correct wind speed at a given number of revolutions. A diametrically magnetised rod magnet type S-04-10-DN proved suitable for this shaft. An integrated circuit sensor detects the absolute position of the magnet and delivers 256 pulses per full revolution of the magnet. This makes it possible to determine the wind speed with an accuracy of up to 0,03 km/h.

A Hall effect sensor type AS5040 on a circuit board

A few words about the magnet used here: I had previously used an S-10-05-DN disc, but that magnet was apparently influenced by the earth’s magnetic field and thus slowed down. The S-04-10-DN rod does not have this issue.

The utilised small ball bearing comes from rollerblades. The viscous oil it contained was replaced with thinner gun oil to facilitate rotation with as little friction as possible.

The magnet is rigidly connected to the anemometer shaft. Then the whole shaft is attached to the ball bearing (bottom).

Shaft with ball bearing (top), magnet (middle) and circuit board with sensor (bottom)

The Hall effect sensor type AS5040 (Austria Microsystems) is soldered in a PVC pipe with the circuit board up. The shaft is lowered into the pipe, magnet first, until the magnet is still 2 mm away from the circuit board. The magnet can now rotate freely above the board without friction.

Lastly, a rigid piece of plastic with three wind meter cups is mounted on top of the pipe.

The wind can set the three cups - and thus the magnet - on the shaft in motion. This movement is gauged by the sensor and the wind speed can be derived from it.

Articles used

S-04-10-DN

Rod magnet Ø 4 mm, height 10 mm, holds approx. 1,1 kg, neodymium, N45, nickel-plated, diametrically magnetised

	10 pcs.	0,54 EUR ea.*
from	40 pcs.	0,45 EUR ea.*
from	80 pcs.	0,41 EUR ea.*
from	160 pcs.	0,38 EUR ea.*
Ask for a rebate from 950 pcs.

Available: 32 710 pcs.

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