madlabs.info

Simple Scope

Technically, this isn't an oscilloscope at all. In a real oscilloscope, a cathode ray tube like in a TV or computer monitor is used. Note that this device will not give you a true wave form. However, this experiment still is cool to look at music.

Materials Required: An old speaker that no-one loves, a laser pointer, small mirror, a sound source.

Construction is very simple. Take the mirror and glue it to the speaker cone. As you can see in the picture above, I tried several mirrors in several places. The big mirror in the middle is one of those "back up" mirrors you can get at auto part stores. Don't buy one! These mirrors magnify the laser pointer, and make it too big to show wave forms very well. It seemed like a good idea at the time...

Another note on mirrors: I cut mine myself from a broken mirror I had saved, but cutting glass is VERY dangerous unless you have the right tools and know how. If you go to a glass shop, more than likely you can beg a scrap or two for free. Dental mirrors that you can buy at drug stores would work well.

Once the mirrors are in place, experiment with the placement of the laser pointer. Remember that even the cheapest little laser pointer can permanently damage your vision! Do NOT look into the laser or the reflection from the mirror! Be careful when aiming and adjusting the laser, unless the idea of being called "Old One-Eye" appeals to you.

As you can see, my laser is mounted with a high tech system: a piece of solid copper wire around 16 gauge. I used the mounting holes of the speaker to attach it. The switch is activated by the tie-wrap. Tape wasn't working very well. This mounting system allows the laser to vibrate along with the speaker, which kind of distorts the waveform, but actually makes it look cooler, in my opinion. The whole montage is glued down with hot glue on a wooden block, with a small piece underneath the speaker top angle it up. Play around with your adjustment before you glue!

These pictures don't really look all that much like it does in real life, but they will serve to give you an idea. Compare some heavy duty rock and roll to some easy listening tunes. Try it at different volumes. I like loud music! I have found a good distance to aim the unit is about ten feet at medium volume for really looking at the wave forms. It's extremely cool to point it far away at night too! And as an added bonus, you can drive your cat insane with it!

If you play with a cat, be as careful of its eyes as you would your own!

The speaker can be hooked up to a stereo or just about anything else. One slick ticket might be to get an old AM/FM radio or cassette deck and pull the grill off the speaker and mount your mirror. This would give you a built in sound source. Otherwise, pretty much any old speaker will work. The one I used was salvaged from an old PA system, which is why it has the paper patch glued on it.

How does it work? The laser beam is reflected by the mirror onto the wall or wherever you are aiming it. The mirror vibrates along with the speaker, since it is glued to it. The movement of the mirror changes the aiming point of the laser in time with the music. For more information on how a speaker works, click HERE.