# Help me with Voltage to Frequency problem

Discussion in 'The Projects Forum' started by electrobuzz, May 10, 2009.

1. ### electrobuzz Thread Starter Member

May 10, 2009
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Hi, thats my first post in the forum.

I'm new to electronics and i would like you to help me with a small project.
I want to make a circuit in which i will have a fan (like those in pc's or just a motor) and according to the speed it will spin because of my blow , a speaker in the circuit will produce a tone that when the fan spins faster the frequency goes up.

2. ### PRS Well-Known Member

Aug 24, 2008
989
35
You can spin an alternator and its output will be a sinewave with a frequency determined by the speed of rotation. So if you spun it with a variable speed motor you'd produce a tone that varied in pitch by the speed of rotation.

3. ### zero_coke Active Member

Apr 22, 2009
294
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For this project you would need a Variable Frequency Drive (VFD) to control the RPM of the fan to make different sounds at different speeds.

4. ### CDRIVE Senior Member

Jul 1, 2008
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Is this a class assignment?

5. ### electrobuzz Thread Starter Member

May 10, 2009
14
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Thank you for you replies.
But i don't want to have just different frequency for different motor rpm, but i want when I rotate the motor (which will not be spining on itself) the frequency to change. And i want to have a tone and when the motor don't spin, which tone's frequencu goes up when i start to rotate the motor ( blowing to the fan)

6. ### t_n_k AAC Fanatic!

Mar 6, 2009
5,448
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Unfortunately I don't understand what your requirement is. Maybe others are in a similar situation. Would you kindly restate the problem using a different wording perhaps - a simple diagram is always helpful.

7. ### electrobuzz Thread Starter Member

May 10, 2009
14
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Oups , sorry for the wording, excuse my english.
I made a diagram that beleve shows what i want .

The motor has a fan. When i set it to motion by blowing to the fan , I want to have a linear correlation (if possible) between frequency and velocity.

File size:
21.7 KB
Views:
19
8. ### CDRIVE Senior Member

Jul 1, 2008
2,223
99
It would appear that the OP wants to demonstrate (using a speaker as an output indicator) that a small blower will output current (like an Alternator) at a frequency proportional to the RPM.

9. ### eblc1388 Senior Member

Nov 28, 2008
1,542
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I think the OP wants to use a simple fan as an anemometer, with variable sound pitch as output.

A stationary fan connects to a circuit producing a 1KHz tone. If he blows on the fan blades to make it spin, he wants the circuit to give increasing frequency output to speaker as per rotation speed of the fan. Faster spin, higher frequency note from speaker.

10. ### electrobuzz Thread Starter Member

May 10, 2009
14
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Exactly that i want.

Last edited: May 11, 2009
11. ### CDRIVE Senior Member

Jul 1, 2008
2,223
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How does a stationary fan (not rotating) produce 1KHz?

12. ### PRS Well-Known Member

Aug 24, 2008
989
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Electrobuzz, I think I understand you now. Your interest is in measuring wind speed using a transducer that produces a frequency that is linearly related to wind speed?

I don't know that such a device is not commercially available, but it seems that you could make one with a little ingenuity. I should think you'd want to make an easily turned 2 pole alternator with windings of magnetic wire. Then output this into a linear amplifier, or digitize the signal using a comparator. Once the signal is digitized it can be analyzed by digital logic devices.

13. ### electrobuzz Thread Starter Member

May 10, 2009
14
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Not the fan. The circuit produce 1KHz itself, and the motor when is setted to motion the frequency changes.

14. ### electrobuzz Thread Starter Member

May 10, 2009
14
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Yes . That's what i want.

Could you help me more with logic devices needed, and about the assembly?

15. ### PRS Well-Known Member

Aug 24, 2008
989
35
There are so many electronics people nowadays automatically think PIC microcontroller as soon as a situation like this comes up. But there are often better ways. I think this is one of those cases. But before I can really determine this I need to know what kind of output you want. If it's to be processed by way of logic in a sophisticated manner, then the microcontroller might be the best way. But if you just want to get a simple frequency versus windspeed, then there is a more simple approach. I mean this latter approach is like hooking a frequency counter up to your transducer and consulting a table or formula of frequency = windspeed. And in this case an experimental approach involving finding a suitable transducer with a corresponding table or formula is the key.

16. ### hobbyist Distinguished Member

Aug 10, 2008
773
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how about a transistor oscillator to idle at 1khz. then put the fan in the bias circuitry to alter the frequency of the oscillator.

17. ### electrobuzz Thread Starter Member

May 10, 2009
14
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I want by measuring the output frequency to be able to find the windspeed. The idea is to connect the output to an audioin of pc or other device and see the frequency.

18. ### CDRIVE Senior Member

Jul 1, 2008
2,223
99
You would be better of constructing your own rotating blade with output being derived from a Hall Effect or IR detector. This is how portable tachometers work.

19. ### PRS Well-Known Member

Aug 24, 2008
989
35
CDrive has the right idea. There are many ways to create a pulse train as a function of rotation. But why do you have to have 1kHz when there is no rotation? That just complicates the problem. But in this case you might make an oscillator that puts out 1kHz and send its output to a mixer. The other input to the mixer is pulse from a rotating machine. The output of the mixer should be 1kHz plus or minus the frequency of the rotating transducer. Use a filter to grab the sum. Then wind velocity = 0 corresponds to 1khz and wind speed is 1kHz+pulse speed. This project requires experimentation in order to deternmine the relationship between rotational speed and wind speed.

Last edited: May 12, 2009
20. ### electrobuzz Thread Starter Member

May 10, 2009
14
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Yes , i understund the expirimation part about the relation of rotational speed and wind speed. But the output of the mixer ( what mixer? - i am very new to electronics ) will be the sum of frequencies?

-- edit

i will have sine wave? or pulse?