# Anemometer / Wins speed meter

Hello, I am building a mini weather station using 2 arduinos, one for the station and one for the receiver and showing of the data and transmitting it over the internet. The thing is I need to make the wind speed/direction sensor as small as I am able to. I know that normally they work by using a reed swtich and getting the frequency it gets atcivated, calculating the wind speed that way. What I was thinking about was using a small motor with almost no resistance and reading the current it produces. My question is if this current in linear in proportion to the motor turning speed.

Thanks, Renato Silva

My question is if this current in linear in proportion to the motor turning speed.

The voltage produced is linearly proportional to the motor turning speed.

Brushed DC motors are very commonly used as small generators in anemometers, and they can drive a wind speed indicator meter directly, with no additional parts except for a resistor to calibrate the system.

What sort of motor are you going to use? A brushed motor will have some turning resistance due to the brush pressure on the commutator, which will make low wind speed measuring difficult.

I was thinking Abou a really small DC motor o computer fan. What you think?

Computer fan motors are brush less DC motors which don’t work in reverse, ie they won’t work as generators.
A very small brushed motor will work,but you will have to measure the rotational resistance caused by the brush pressure to determine the minimum wind speed that can be measured.

And how can I do that?

Build your anemometer, then on a wind-still day, drive around with it attached to the roof of an automobile.

That will allow you to see if it behaves properly and also to calibrate it accurately.

I will do that. Thanks. Another thing, do the "propellers" have to have spoon shaped to keep it linear or can it be any other shape?

Another thing, do the "propellers" have to have spoon shaped to keep it linear or can it be any other shape?

I don't know, but if you try some other shape, the same technique used for calibration will tell you if the response is linear.

In the Arduino can I connect the motor directly to an analog pin and read it? Of course using a voltage divider to make sure the voltage on the input pin is under 5V.

Yes, making sure you know which motor lead is positive. Also connect the negative motor lead to the Arduino ground.