We thought that making things levitate in mid-air by the power of sound was a little bit more like magic, or at least required fancy equipment. It turns out that you can do it yourself easily enough with parts that any decent hacker’s closet should have in abundance: a motor-driver IC, two ultrasonic distance pingers, and a microcontroller. This article shows you how (translated here, scroll down).
But aside from a few clever tricks, there’s not that much to show. The two HC-SR04 ultrasonic distance sensors are standard fare, and are just being used as a cheap source of 40 kHz transducers. The circuit uses a microcontroller, but any source of 40 kHz square waves should suffice. Those of you who could do that with a 555 (or a Raspberry Pi), this one’s for you! A stepper motor driver bumps up the voltage applied to the transducers, but you could use plain-vanilla transistors as well.
It’s all the little details that count, however. You need to position the two ultrasonic drivers fairly precisely to create a standing wave, and while you can start at 8.25 mm and trial-and-error it, the article demonstrates using an oscilloscope to align the capsules by driving one and reading the signal out of the other and tweaking them until they’re in phase. Clever!
The author also takes the ultrasonic-transparent grille from one of the unused receivers and uses it as a spoon to help position the styrofoam bits in the sound waves. We always wondered how you’d do that!
It turns out that it’s easy to make a DIY ultrasonic levitation desk toy, and none of the parts are expensive or critical. The missing ingredient is just the gumption to try it, and now we have that, too.
As cool as they are, the HC-SR04 modules aren’t perfect for all distance sensing applications. Here’s everything you need to know about them, including hacks to make them work up-close. And since HC-SR04 sensors come cheapest in ten-packs, you’ll be wondering what you’re going to do with the other eight. That problem has apparently also been solved.