If You Build It, Santa Will Come

Kits for building musical pencils, Theremins, crystal radios, and shortwave radios

Photo: Randi Silberman Klett

This is part of IEEE Spectrum's Special Report on IEEE SPECTRUM'S 2009 Holiday Gift Guide

What better way to introduce a young person to the joys of engineering than by giving a gift that you construct together? I tested four suitable kits. Two are for unusual electronic musical instruments, and two are for dabbling in radio.

The Drawdio turns a pencil—or a pencil sketch—into a musical instrument that sounds something like a kazoo. The kit, available from Adafruit Industries, costs just US $17.50, takes only an hour or so to assemble, and includes everything you need but the AAA battery. If you have any experience soldering components to a printed-circuit board, assembly will be a snap. The hardest step is pushing a thumbtack (included) into the end of a pencil (also included) to make electrical contact with the graphite that runs down its center.

Drawdio is simply an oscillator whose frequency is controlled by the resistance of the circuit path connecting the part of the pencil you grip with the attached thumbtack. You can make sounds by grabbing the pencil in one hand and touching the tack with the other, but that's not the fun way to use it. Instead, draw a heavy line, laying down a lot of conductive graphite as you go. Then press on one end of the line with the forefinger of your free hand while holding the tip of the pencil on the other end of the pencil line. Apply adequate pressure, and Drawdio will emit a low buzz. Moving the tip of the pencil closer to your finger reduces the resistance of the frequency-control path, shifting the sound to a higher pitch. So it's not hard at all to generate a simple tune. If you have trouble hitting the right notes consistently, just mark their positions on the line.

If you really want to impress a musical protégé, splurge on a kit for a theremin, the granddaddy of all electronic musical instruments, whose eerie, melancholy sound is a hallmark of old science-fiction movies.

Photo: Randi Silberman Klett

Thanks to the late Robert Moog, a pioneer of electronic music, you can buy the Etherwave Theremin kit, available from Moog Music for $359; many online distributors sell it for less. The kit includes a fully assembled printed-circuit board, so all you have to do is wire up the front panel and two antennas, which sense the position of the player's hands, thus controlling pitch (right hand) and volume (left).

The Etherwave kit comes with a handsome oak cabinet, but I was disappointed by the sloppy fit between the top and bottom pieces. Most of my effort went into rebuilding the cabinet. Check your kit and send it back if the woodwork is botched.

That shortcoming aside, this kit is a joy. The theremin, unlike most instruments, has no keys or frets for your fingers to land on. Hitting the right note is quite tricky because you have nothing but your ear and an eyeball estimate of the distance to the pitch antenna to guide you. Like chess or Go, it takes minutes to learn and a lifetime to master. I quickly rendered a recognizable "Mary Had a Little Lamb," all the while chuckling at the notion of playing music without having to touch the instrument. My goal is to master "Over the Rainbow," which should keep me busy for some time yet. Fortunately, the kit's copious documentation includes a video on theremin-playing technique.

 

Those less musically inclined might prefer kits for radios. You could, for example, put together a classic crystal set, which in a bygone era would have involved an actual crystal, probably a lump of pyrite or galena. In most of today's inexpensive kits, a diode serves as the detector, and a few other components complete the bare-bones radio circuitry, which drives a high-impedance earphone with nothing other than the energy picked up by the antenna.

Photo: Randi Silberman Klett
Little Wonder Crystal Radio Kit

To explore such a simple project, I purchased The Little Wonder Crystal Radio Kit from the Xtal Set Society for $16.95. It took only minutes to assemble, and it worked right off the bat. But its performance is so underwhelming—mine could pick up only one local station—that I worry a young person would be turned off by the experience.

Photo: Randi Silberman Klett
Model 1253 Nine-Band Regenerative Shortwave Receiver Kit
Ten-Tec; $89;
http://store.tentec.com/kits/receivers/#1253

I recommend instead Ten-Tec's model 1253 nine-band receiver kit, which you can order directly from the manufacturer for $89. It spans from 1.8 to 22 megahertz and thus picks up both shortwave and ham bands. What's more, because it has a regenerative detector, it has excellent selectivity and can receive AM, single-sideband, and continuous-waveform broadcasts. The front-panel controls include frequency, RF gain, and audio volume, as well as a somewhat mysterious regeneration adjustment. You can have hours of fun tuning in to the world by twiddling these dials. It's not often you can share in an experience that pretty much went out of fashion decades ago.

This kit is very well designed and has an excellent set of instructions, though most people will require a good weekend of work to get it all put together. The hardest part for me was learning to use the regeneration control after I finished assembly. Initially, I was disappointed with how few stations I could pull in. Then I got the hang of delicately adjusting the amount of feedback used in the detector—something you don't do on modern radios—and the world opened up with nothing but a 5-meter wire antenna draped over some furniture in my living room.

The radio is housed in an attractive enclosure, and it has a built-in speaker as well as an earphone jack. It can run off batteries or a wall wart (neither is included). All in all, it's much more than a demonstration project—you end up with a very practical radio set.

If none of these kits tickle your fancy, search the Net for others that do. Exposing a young person to the feeling of having built a piece of electronic gadgetry is well worth the occasional dud. Hopefully, it'll spark wonder yet demystify electronic technology. And that would be the best gift of all.

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