square waves into sine waves... any ideas????

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bully_victim

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can anybody tell me how i can compare two frequncies using beat frequencys???
im trying to make a guitar tuner as my HNC project and im generating a sqaure wave from and oscillator circuit,which im using as a reference frequency to compare with an input from my guitar, which, produces a sinusodual output.
if compare the square and the sinewaves i am not able to turn a bulb(indicator) on and off completly so i do really need two sine waves....
after all that any ideas
 

Cool,i'm working on a distortion pedal,good luck
 
A square wave is a complex wave, composed of sine waves of the fundamental frequency, plus every odd harmonic (3rd, 5th, 7th, 9th...) up to the infinith harmonic (in theory, anyway).

If you feed a square wave into a low pass filter, tuned just above the fundamental frequency, you should get a pretty clean sine wave out.
 
For reference, here is a basic active low pass filter:
 

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In the function generators first feed the square wawe to integrator. The output is triangle wawe, and with diode limiter circuit make sinus.
 
Seems to me that it would be simpler to convert your guitar output to a square wave using a comparator with hysteresis (Schmitt trigger), and then compare the frequencies of the two square waves.
 
im thinking of using beat frequencies aswell..... think that this is a good idea???
any other ways of comparing the two frequencies would be most apprieciated....
 
Why use filters ?

Is there a reason why you are using a square wave?
Will this be for tuning a single guitar string or are you hoping to measure beat frequencies from all six strings against one/six oscillators ?
Do you have a diagram or fuller description of your idea ?

As this is a college assignment (yours, not ours!) I want to see what your thinking is before I suggest anything that could alter your current direction.
There is never just one way of doing these things !
:wink:
 
If you go with Phasors idea of low pass filter, you really should make a band pass filter tuned to the frequency you want. The low pass will pass all lower frequencies as well and add to the distortion. Also, if you use the diode limiter version (from triangle) wave be prepared for significant distortion there too.
 
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