Need to make a triangle to sine wave converter

[TheJokerV]

Hey everyone, I need to build a triangle to sine wave converter. Honestly I'm completely lost. Does anyone have any ideas? I would really appreciate any advice or suggestions you could give me. Thanks.

 

[dknguyen]

Hey everyone, I need to build a triangle to sine wave converter. Honestly I'm completely lost. Does anyone have any ideas? I would really appreciate any advice or suggestions you could give me. Thanks.

A triangle wave is very very close to a sine wave. A 30kHz triangle wave is pretty much a 30kHz sine wave with a few other harmonics (sine waves of higher frequencies that are multiples of the fundamental frequency added into it).

So all you really need is a filter with a cutoff frequency that is higher than the frequency of the triangle wave, but not too high so it can supress the higher frequency sine-waves that make up the triangle wave so you are only left with the lowest one.
https://en.wikipedia.org/wiki/Triangle_wave

But is the sine-wave input a constant frequency? Or can it vary considerably? If it does, then you will need to be able to change the cut-off frequency for your filter which might make things a bit harder. I'm thinking of something that detects when the triangle wave crosses zero to figure out the frequency of the sine-wave in order to automatically set the cut-off frequency of the filter, but I have a feeling this is really over complicating things. SOmeone else may be able to help you more.

It's the same for a square wave. You filter out enough frequencies, and you end up with the fundamental sine-wave whose period will be the same as the original square wave.

EDIT: You've learned about the Fourier series right? How every signal is a bunch of sine waves of different frequencies and amplitudes added up properly?

 

[TheJokerV]

Well the thing is that the input will be a constant-frequency triangle wave and the output has to be a sine wave. What do I do in this case? I can't filter out voltage fromt he sine wave right? Also what kind of filter would you suggest?

 

[eng1]

Hey everyone, I need to build a triangle to sine wave converter. Honestly I'm completely lost. Does anyone have any ideas? I would really appreciate any advice or suggestions you could give me. Thanks.

Google for 'breakpoint method' or 'sine wave shaper'. Basically these circuits are operational amplifiers with diode/resistor networks in the feed-back loop. Each diode turns on when the input voltage (triangle) reaches a 'breakpoint'. In practice, this changes the close loop gain of the op amp in function of the input voltage.
The output voltage (sine) can be filtered (the same stage can do that, a 1st order pole is fine), achieving low distortion (say < 3% typically).

 

[Hero999]

If it's a fixed frequency, then a simple RC filter will do fine.