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.
http://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?

 

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?

 

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).

 

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

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