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### Topic: Anemometer / Wins speed meter (Read 431 times)previous topic - next topic

#### scottbear

##### Nov 07, 2015, 12:57 am
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

#### jremington

#1
##### Nov 07, 2015, 02:25 am
Quote
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.

#### mauried

#2
##### Nov 07, 2015, 04:49 amLast Edit: Nov 07, 2015, 04:49 am by mauried
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.

#### scottbear

#3
##### Nov 07, 2015, 09:06 am
I was thinking Abou a really small DC motor o computer fan. What you think?

#### mauried

#4
##### Nov 07, 2015, 10:56 am
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.

#### scottbear

#5
##### Nov 07, 2015, 12:28 pm
And how can I do that?

#### jremington

#6
##### Nov 07, 2015, 05:25 pm
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.

#### scottbear

#7
##### Nov 07, 2015, 05:49 pm
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?

#### jremington

#8
##### Nov 07, 2015, 07:03 pm
Quote
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.

#### scottbear

#9
##### Nov 08, 2015, 11:57 am
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.

#### jremington

#10
##### Nov 08, 2015, 05:42 pm
Yes, making sure you know which motor lead is positive. Also connect the negative motor lead to the Arduino ground.

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