# How to convert Square Wave to Sinewave

1. ## How to convert Square Wave to Sinewave

I am getting square wave from 555 timer IC
I want to convert it into sine wave and then feed it into speaker

Kindly tell me how to convert Square wave to sine wave

2. ## Re: How to convert Square Wave to Sinewave

If you need a low cost solution, you could use a high order active analog filter (LOW PASS) after the 555. What you will obtain is not a perfect sinewave but it might work depending on your application.
Another option would be making an analog sinewave generator like this one: A Sine Wave Generator

Good luck!

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3. ## Re: How to convert Square Wave to Sinewave

Basically i am having square wave of 400 Hz
I want to convert it into Sinewave and listen on speaker,
Kindly tell me which approach is good and easy to patch on breadboard

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4. ## Re: How to convert Square Wave to Sinewave

The fundamental component of your square wave is the wanted sinusoidal signal.
Therefore - as proposed above - use a lowpass and supress all higher harmonics as much as needed.
The low pass order is determined by the accuracy you want to obtain (measured as THD).

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5. ## Re: How to convert Square Wave to Sinewave

Ok thanks
Can u give me link of some site which can show me circuit for low pass infreq range 300 Hz to 600 Hz

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6. ## Re: How to convert Square Wave to Sinewave

Texas Instruments Filter Pro is one of many available tools supporting the design of active filters. Active Filter Design Application - FILTERPRO - TI Software Folder

7. ## Re: How to convert Square Wave to Sinewave

For deriving sinusoid wave ,you'd better pick the filter type as Cauer (also be called as Elliptic) to reduce the order of the filter.

8. ## Re: How to convert Square Wave to Sinewave

If you just want to listen the 400Hz tone on the speaker then you can directly give 400Hz square wave directly to the speaker.

9. ## Re: How to convert Square Wave to Sinewave

yes i know i am also listening it on my speakers but i want to convert it into sine wave

Somebody wrote that a simple RC circuit can convert square to sine wave
How to calculate values of Resistor and Capacitor for 300 Hz Square Wave

Kindly explain me their connectivity

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10. ## Re: How to convert Square Wave to Sinewave

Originally Posted by moonnightingale
yes i know i am also listening it on my speakers but i want to convert it into sine wave

Somebody wrote that a simple RC circuit can convert square to sine wave
How to calculate values of Resistor and Capacitor for 300 Hz Square Wave

Kindly explain me their connectivity
That`s nonsense. A simple RC circuit (first order lowpass) cannot change a squarewave into a sinusoidal signal. In theory, you would need an IDEAL lowpass (brickwall response) to remove all harmonics. As I told you earlier, a lowpass of order n=2...4 will do the job - depending on your THD requirements.
Regarding Narshben`s suggestion, I doubt if an elliptical filter is the best choice for this purpose due to its complexity.

11. ## Re: How to convert Square Wave to Sinewave

Originally Posted by LvW
That`s nonsense. A simple RC circuit (first order lowpass) cannot change a squarewave into a sinusoidal signal. In theory, you would need an IDEAL lowpass (brickwall response) to remove all harmonics. As I told you earlier, a lowpass of order n=2...4 will do the job - depending on your THD requirements.
Regarding Narshben`s suggestion, I doubt if an elliptical filter is the best choice for this purpose due to its complexity.
Can u send me circuit diagram for any filter
Thanks

12. ## Re: How to convert Square Wave to Sinewave

Originally Posted by moonnightingale
Can u send me circuit diagram for any filter
Thanks
For "any filter"? Do you know that there are several books dealing only with filter design?
And - what about Internet search?

13. ## Re: How to convert Square Wave to Sinewave

From what I remember, there is a triangular wave available at the timing inputs of a 555.

Buffering this with an op-amp or Emitter follower stage and then using a 'triangle to sine' convertor comprising a series of back to back diodes with series resistors in the negative feedback path to shape the gain within an inverting op-amp stage can give a good approximation of a sinewave with distortion below 1%.
I did use this method some years ago for an 'internal' reference signal, to avoid amplitude bounce as with Wein Bridge oscillators, within an Audio Mixing Desk but unfortunately no longer have the circuit info.

Think this will be simpler than trying to use filtering of a squarewave to output a sinewave from your circuit....... although a simple lo-pass passive filter following the 'triangle to sine' convertor will further improve the residual sinewave distortion giving you a purer tone for listening tests with the 'speakers which you want to achieve.

Seem to remember that there is some good info on this approach in the Analog Devices Application Notes, but can't remember which one(s) - hopefully someone else can remember where this info is?

Hope this assists
Mik

14. ## Re: How to convert Square Wave to Sinewave

A 400 Hz low-pass. The yellow magnitude response is valid for the given component values.

15. ## Re: How to convert Square Wave to Sinewave

Originally Posted by FvM
A 400 Hz low-pass. The yellow magnitude response is valid for the given component values.

Actaully i am having several frequencies which are controlled through push button
the range of my frequencies is from 250 Hz to 600 Hz

will this filter work for whole range of frequencies

I just tried this circuit which i got from internet. I changed the values of Inductor and capacitor by hit and trial and now i am getting perfect sinewave for almost whole range

can u kindly explain me this circuitry. how it is producing the sinewave
Pics are attached

16. ## Re: How to convert Square Wave to Sinewave

Actaully i am having several frequencies which are controlled through push button
the range of my frequencies is from 250 Hz to 600 Hz

will this filter work for whole range of frequencies
That's difficult, because 3rd harmonic of 250 Hz is very near to 600 Hz. You didn't yet mention this requirement, by the way. But I assume, that you're able to find suitable filters from literature. The TI FilterPro software is one of many available resources.

To generate a sine signal over a certain frequency range, a RC generator tuned with two resistors, e.g. a stereo potentiometer, seems more reasonable in my view. There are many previous threads about sine generators at Edaboard.

17. ## Re: How to convert Square Wave to Sinewave

Originally Posted by FvM
That's difficult, because 3rd harmonic of 250 Hz is very near to 600 Hz. You didn't yet mention this requirement, by the way. But I assume, that you're able to find suitable filters from literature. The TI FilterPro software is one of many available resources.

To generate a sine signal over a certain frequency range, a RC generator tuned with two resistors, e.g. a stereo potentiometer, seems more reasonable in my view. There are many previous threads about sine generators at Edaboard.
ok thanks FVM
Kindly comment about the circuit which i have uploaded
How it is giving so good response

Can u explain it

thanks

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18. ## Re: How to convert Square Wave to Sinewave

WIth unloaded output (is it?), it's far from a regular low pass filter, e.g. having 10 dB peaking at 500 Hz. This suggests, that the filter requirements aren't actually very critical.

19. ## Re: How to convert Square Wave to Sinewave

ok thanks
can u kindly explain me function of inductor and capacitor in this circuit

20. ## Re: How to convert Square Wave to Sinewave

The filter is a passive 3rd order low-pass, the corresponding LC implementation of the OP filter I posted above. My adjusting the L and C values, you can give it different filter characteristics.

Some basics about passive filters can be found here: Lessons In Electric Circuits -- Volume II (AC) - Table of Contents

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