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# turn a square wave froma 555 into a sine wave?

I would like to know how to smooth out a square wave to turn it either into a sine wave or at least a triangle wave. Or if it's not possible i would like to know how to make a sine wave generator to use as a lfo thing for a home made synth.

Thanks,

Josh1324

PS. It has to be analog, im not getting into microcontrollers or anything digital.

Feed the square wave into an integrator will make it into a triangle wave. The classic way to make a sine wave is with something like a wein bridge oscillator, but these days, if you can find them, the XR8038 is/was a great part.

For the purest waveform, you generate a sine wave directly, not clip up a 555.

Most of the time, I'd use a DDS chip, but if you're staying analogue, your choices are a bit more limited.

Look for the really old electronics mags from the late 60s-70s when everyone was trying synthesiser designs.

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Thanks for the answer, but could you go into more detail with the "integrator", because i don't fully get it. I looked it up, but it's just saying stuff about calculus.

Thanks,

josh1324

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Jack's link is a start. for you, one problem you'll have is the integrator will need bi-polar inputs, so you're actually better off making the square wave with an op-amp, using bi-polar supplies, than a 555.

The integrator effectively adds up its input constantly, so if you imagine that the input square wave is of unit height, its adding 1+1+1+1+1+1+1+1 - which is increasing linearly, and then adding -1-1-1-1-1-1-1-1-1-1 decreasing linearly - and there you have a triangle wave.

Like I said, the old synth stuff is the place to go for details.

Steve

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actually, i need the sine wave to go from 0v - +9v because i'm making an lfo for my synth... i forgot to include that...

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That depends on your LFO design. In general, split rails make analogue circuits like synths MUCH simpler.

Steve

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Calculus is divided into two mathematical branches,

Differential a study of diffrerences in grose fisioligy branch,

Integral a study of L&M bounds strength branch,

Once you spend two or more years of study

then a great many questions of this nature become as you understood.

All of electronics even hanging wires is described by math and unferstood because of imaginaru numbers.

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The usual trick for making an integrator involves an op-amp, an R, and a C. Here:

http://en.wikipedia.org/wiki/Operational_amplifier_applications#Inverting_integrator

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Look at the link in my answer to this question, you'll find it there.

Qa

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Have you looked at the link I provided in the question listed above? It shows you how to use a single 555 to make:

1.) square

2.) integrator

3.) triangle

4.) sine

It's all there, complete schematic with parts and build notes. Can't ask for more.

Qa

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Hi Quercus austrina, I know this was a long time ago, but I just found myself in need of a function generator, and followed your link, you mentioned it specifies everything but really it doesn't specify the frequency range that this circuit has. so my question was, how do I determine the frequency and if I wanted to how do I change it?

Thanks a lot

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Try this calculator from Bill Bowden. He's a hobbyist's best friend.

Just put in the min and max values for your resistors and the capacitor value. You will get the range of those components, albeit one step at a time.

Qa

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Hi,

Here again asking silly questions, but I tried the theory and circuit you provided from the calculator, and using my oscilloscope, the pulses aren't proportional, the positive pulse is twice as long as the negative pulse, how can I fix this? I'm using simple values of 1K for resistors and 0.1 for capacitors therefore giving me a frequency of 4.8KHz ..

Refer to this crude example, but you can prob get the idea

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All the help is appreciated!

Thanks in advanced

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hmmm in the reply post it doesn't look properly... ok positive pulse width is two times the negative pulse width...

thanks

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Thanks! I'll give it a try

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