# Final Project: Harmonics

Discussion in 'The Projects Forum' started by PMB917, Mar 9, 2006.

1. ### PMB917 Thread Starter New Member

Mar 7, 2006
5
0
I'm putting together my final project for the CET program at ITT Tech. We're supposed to come up with an original project that proves we've learned something.

One of my teachers seems to be obsessed with finding diffrent ways to convince the class that square waves are made up of sign waves. We do not have a spectrum analyser so I came up with this idea. (attached is a rough block diagram
of my project)

Three oscillators (sine, square, and sawtooth, all running at 5 hz) are fed into a multiplexer that is configured with a ring counter to cycle through the oscillators 5 seconds at a time.

The output of the multiplexer splits off to five bandpass filters (5hz, 10hz, 15hz, 20hz, and 25hz, each having progressive gains) with LEDs attached to the filters output.

In theory, or at least in my wacky mind, this is what should happen.

When the output of the multiplexer is the sign wave(assuming the sine wave is pure), the only LED that will blink will be at the end of the 5hz bandpass filter.

When the output of the multiplexer is the square wave, the only LEDs that will blink will be the ones at the output of the 5,15, and 25hz bandpass filters.

When the output of the multiplaxer is the sawtooth wave, all the LEDs should blink at there respective frequencys.

What do yall think? Got any thoughts/suggestions? I'd love to hear anything.

Any suggestions on a better output indicator than an LED?

P.S. Dam, my spelling sucks!

2. ### Papabravo Expert

Feb 24, 2006
9,905
1,723
I think you are going to spend a great deal of time fabricating this project for very little payoff. The theoretical idea that square waves are made up of sine(not sign) waves requires an infinite number of them and the square wave in question has edges with infinite slope. It is interesting theoretically, but of little practical value.

The usual method of producing square waves, as you already know, has nothing to do with summing an infinite number of sine waves. Triangle waves are produced by integrating square waves. Ho-Hum.

If I were you, I would try for something easy to fabricate. You might try something with a PIC eval board or a BASIC Stamp. The idea would be to try changing some component or some program to demonstrate a result. If you haven't reached microprocessors yet, then your options appear to be more limited.

Along the lines of bandpass filtering is the DTMF system used by touch tone telephones. There are now single chips which do the encodeing and decoding but you could fabricate a simplified version. If you do the research it would certainly prove that you had learned something.

Good Luck

3. ### thingmaker3 Retired Moderator

May 16, 2005
5,072
6
Another option would be to make a good quality tunable filter. Put your square wave (or whatever) in and hook the o/p to an O-scope. Turn the knob and watch the components come up.

Sort of a "manually operated" version of the spectrum anyliser.