# Changing voltage into frequency using OpAmp

Discussion in 'Homework Help' started by alpyurtsever, Jan 1, 2011.

1. ### alpyurtsever Thread Starter New Member

Nov 18, 2010
12
0
Hi, do you have an idea to convert voltage into frequency but using only OpAmps and some basic circuit elements like resistors, capacitors, inductors and diodes?

Or, how can i change the duty cycle of a square wave, with respect to the voltage. In other words, I want a converter like voltage to duty cycle.

I thought to do it like following;

I will take the integral of square wave, and obtain a triangular wave, using integrator circuit.
Then using a comparator circuit, I will reconstruct the square wave.
But, the problem is that, I want 0 duty cycle when I have a 0 voltage to compare, and increasing the voltage, I want to obtain greater duty cycles. But this method gives 50 duty cycle, at voltage 0.

Thank you

Last edited: Jan 1, 2011
2. ### #12 Expert

Nov 30, 2010
16,302
6,812
Google "voltage to frequency converter circuit"

3. ### alpyurtsever Thread Starter New Member

Nov 18, 2010
12
0
Yes, I have done it, but as I have specified, it must be obtained using Opamps, not any other integrated circuits or timers. But the google results are some exaples with timers or integrated circuits.

4. ### #12 Expert

Nov 30, 2010
16,302
6,812
I have an idea to carry salt across the desert using only bunny rabbits.

Tell me please how to do that?

What frequencies do you want?
What voltages do you have?
Is the change linear or logrythmic?
Why can you only use chips that are over 30 years old?

Last edited: Jan 2, 2011
5. ### alpyurtsever Thread Starter New Member

Nov 18, 2010
12
0
Because it is an high school project and only that chips over 30 years old are allowed to use.
I have voltages up to 20, I am able to split it, so it doesn't matter in what voltages it works. I can obtain any voltages up to 20.
Change doesn't matter, it can be linear, logarithmic, or however you want. I would prefer linear one anyway.
I want to operate it at low frequencies, like that the greatest period will be 1 second.

I hope I have clarified my point. Maybe now you can find a sloution, whereas I didin't want a solution, I have just asked for an idea, so I don't think that you have to know all these details to find it.

Moreover, I have an idea for you to carry salt across the desert using only bunny rabbits. But I should know the followings;

What kind of a salt you want to carry?
Your rabbits are male or female; pink or white?
Are these rabbits are just walking? Or, can they also run and jump?
Why can't you use spaceships?

Thank you in advance.

6. ### bertus Administrator

Apr 5, 2008
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alpyurtsever likes this.
7. ### Kermit2 AAC Fanatic!

Feb 5, 2010
3,791
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The black and white of the matter being:

You post up what you have accomplished toward this goal, first.

We will help you 'complete' the work and to understand it.

Demanding answers will seldom get you the kind of answers you want.

8. ### alpyurtsever Thread Starter New Member

Nov 18, 2010
12
0
Thank you at first, as I have already indicated, (in order to change duty cycle with respect to my reference voltage) ;
I have used an square wave generator (http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/square.html#c1)
And then, I have integrated the ouput of it (http://webpages.ursinus.edu/lriley/ref/circuits/img191.gif)
Afterwards, I have used a comparator, to compare the voltages between the output of integrator and my reference voltage (changing between 0 and 10).
I had struggled because ;
I want 0 voltage output, when my reference voltage is 0. However this circuit gives me 50 duty cycle square wave.

By the way, I have solved my problem by shifting the output voltage of the integrator up, thank you...

(I have also find a similar problem in the forum, so I am sorry about that, I have used the forum search but I thought that it is done using an integrated circuit in that post)

Last edited: Jan 2, 2011