# Inductor measurement - wind meter

#### Episkopianos

Joined Nov 18, 2017
13
Hello, I want to make a wind meter like this one: attached

I opened it and saw that it has an inductor under the fan, and the fan has a magnet in the center so when rotates produces magnetic field and the inductor changes the inductance right?

So can I make this circuit and using arduino to read it?

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#### GopherT

Joined Nov 23, 2012
8,009
Hello, I want to make a wind meter like this one: attached

I opened it and saw that it has an inductor under the fan, and the fan has a magnet in the center so when rotates produces magnetic field and the inductor changes the inductance right?

So can I make this circuit and using arduino to read it?
Yes, you can use the back-EMF pulses from the turning motor. You may have to amplify the pulse before the Arduino will see the pulses.

Then use a counter function to count the number of pulses each second.

You'll have to calibrate it with some standard wind speed because the efficiency of any given blade design will vary.

#### MrChips

Joined Oct 2, 2009
29,849
Hello, I want to make a wind meter like this one: attached

I opened it and saw that it has an inductor under the fan, and the fan has a magnet in the center so when rotates produces magnetic field and the inductor changes the inductance right?

So can I make this circuit and using arduino to read it?
Your objective is not to measure inductance. It is better to look at the inductor as a sensing or pickup coil. The rotating magnet induces a current in the pickup coil. Your objective would be to amplify the signal and convert it into a digital pulse which can be detected by a microcontroller such as Arduino. You then need to count the number of pulses received in a fixed duration and convert that number into wind speed.

#### Episkopianos

Joined Nov 18, 2017
13
Your objective is not to measure inductance. It is better to look at the inductor as a sensing or pickup coil. The rotating magnet induces a current in the pickup coil. Your objective would be to amplify the signal and convert it into a digital pulse which can be detected by a microcontroller such as Arduino. You then need to count the number of pulses received in a fixed duration and convert that number into wind speed.
Wow, thank you both, MrChips I understood now more clear what I have to do, actually I tried something you said but didn't understand until now, attached is the circuit, should that work?

#### MrChips

Joined Oct 2, 2009
29,849
Wow, thank you both, MrChips I understood now more clear what I have to do, actually I tried something you said but didn't understand until now, attached is the circuit, should that work?
No. I said you do not measure inductance.
The first thing you need to do is examine the signal from the pickup coil on an oscilloscope and determine the voltage and shape of the pulse.
Your next step would be to amplify the signal to about 1V or 5V peak-to-peak.

#### Episkopianos

Joined Nov 18, 2017
13
No. I said you do not measure inductance.
The first thing you need to do is examine the signal from the pickup coil on an oscilloscope and determine the voltage and shape of the pulse.
Your next step would be to amplify the signal to about 1V or 5V peak-to-peak.
Ok, I will do that on Monday because I don't have an oscilloscope right now, but just to be sure, the signal which I will see on the oscilloscope will be an AC voltage right ? And after I amplify my signal to 5v peak to peak how do I convert it to a digital pulse?

#### MrChips

Joined Oct 2, 2009
29,849
Ok, I will do that on Monday because I don't have an oscilloscope right now, but just to be sure, the signal which I will see on the oscilloscope will be an AC voltage right ? And after I amplify my signal to 5v peak to peak how do I convert it to a digital pulse?
We'll tackle one thing at a time. Let's see what the signal looks like on an oscilloscope.
Yes it will be AC, but that doesn't mean that it has to go positive and negative. We can amplify and level shift it so that it goes between 0V and 5V (assuming that the Arduino board accepts 0-5V signals). We can input that to the Arduino chip (Atmel ATmega chip).

#### Tonyr1084

Joined Sep 24, 2015
7,554
IS that digital pulses? Or is it a generated analog voltage? I'm thinking it's going to be an analog voltage. Yes, it can be shifted, but I think a more basic approach would be to calibrate the voltage produced at various wind speeds to that it could be read out as a voltage. DC or AC, as long as what it represents is wind speed.

To calibrate, a simple variable resistor (pot) would set the slope. The HARD part would be to calibrate it to a known wind speed. (or maybe not - I just don't know how I'd go about it; but then again, I haven't given it any thought)

#### philba

Joined Aug 17, 2017
959
On a still day take the unit out for a drive.

#### Tonyr1084

Joined Sep 24, 2015
7,554
On a still day take the unit out for a drive.
Not a good option. Air has to accelerate around the vehicle. Unless the sensor is mounted in front of the vehicle with sufficient distance air trying to get around the nose and windshield will be greatly affected. Good idea though.

#### Episkopianos

Joined Nov 18, 2017
13
We'll tackle one thing at a time. Let's see what the signal looks like on an oscilloscope.
Yes it will be AC, but that doesn't mean that it has to go positive and negative. We can amplify and level shift it so that it goes between 0V and 5V (assuming that the Arduino board accepts 0-5V signals). We can input that to the Arduino chip (Atmel ATmega chip).
Hi MrChips, I have an oscilloscope now so I tested the signal but I don't understand, I connected the inductor with a resistor and without blowing on the fan I had a sin wave and when I was blowing on the fan nothing changed or it was so small I didn't see anything.

I also connected the to leads to the multimeter in AC mVolts and the readings were from 0-7mvolts while blowing harder.

Everything is attached. If I did something wrong please tell me and I will do it correct.

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#### MrChips

Joined Oct 2, 2009
29,849
Is this the same fan from the anemometer from post #1?
If this is not the same, give us some information on the specs or where you got this fan.
What is that black component that looks like an inductor?
What is the value of the resistor?

Do you have fluorescent lighting in your room?

#### Episkopianos

Joined Nov 18, 2017
13
Is this the same fan from the anemometer from post #1?
If this is not the same, give us some information on the specs or where you got this fan.
What is that black component that looks like an inductor?
What is the value of the resistor?

Do you have fluorescent lighting in your room?
Yes, its the same fan like post #1 . It's the one that the anemometer had. I just took it out.
The black component is an inductor, I got it from Amazon, I will attach the inductor with the circuit from the anemometer. the resistor is 150ohm.
Yes, the lab has fluorescent lighting.

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#### philba

Joined Aug 17, 2017
959
OK, so first the signal you are seeing is interference from the AC mains.

Now you should understand that you can't just put an inductor into this circuit and have it work. The coil in the meter is probably a pickup coil and as such it (or something similar) needs to be placed close to the magnet with proper orientation. Look at the positioning in the meter and mimic that. I don't know if a random inductor will work or not but I know it won't if you don't get it the right location.

#### MrChips

Joined Oct 2, 2009
29,849
As philba says, you cannot use an off-the-shelf inductor. You will have to wind your own pick-up coil.
As philba says, what you are seeing on the scope is probably noise from the fluorescent lighting.

Joined Jul 18, 2013
28,048
I built one for a school many moons ago, just a simple slot opto, also there is a hall sensor, why do you need inductor to measure wind speed?
Max..

#### philba

Joined Aug 17, 2017
959
It's just a cheap pickup coil. Probably cost less than a HE sensor or optointerrupter.

#### MrChips

Joined Oct 2, 2009
29,849
Put an IR LED on one side of the fan blades and an IR detector on the other side and detect the signal as the fan blades interrupt the IR beam. Straight to digital.

#### Episkopianos

Joined Nov 18, 2017
13
OK, so first the signal you are seeing is interference from the AC mains.

Now you should understand that you can't just put an inductor into this circuit and have it work. The coil in the meter is probably a pickup coil and as such it (or something similar) needs to be placed close to the magnet with proper orientation. Look at the positioning in the meter and mimic that. I don't know if a random inductor will work or not but I know it won't if you don't get it the right location.
That's what I think as well, it's a pick up coil, so what would be a proper circuit to make this work with arduino like the wind meter, I can read the milli voltage on the multi meter, do you know? I'm positioning the fan as it was on the wind meter by holding it.

#### philba

Joined Aug 17, 2017
959
The coil should be as close as possible to the magnet without interfering with the fan. I'd experiment with the correct orientation.