Piezo Elements for Percussive Input

Harry Partch and Piezo Instruments

Lauren Hirsh, a WSU percussion student, WSU Internet radio goddess, and all-’round CRATEL regular, is involved in a performance of Harry Partch compositions this spring. Partch composed for new instruments he created, and the percussion department is attempting to build at least one or two of them for the concert. Lauren is taking on the task of building one, I believe the boo.

The boo is a marimba-like instrument made from tuned bamboo tubes arranged in six ranks. Rather than try to reproduce the tonal qualities of the original instrument through physical means, consideration is being given to building an input interface and using electronic reproduction of the boo sounds. In other words, Lauren wants to build a synthesizer keyboard shaped like a marimba. And several of us involved in CRATEL are intrigued by the challenge.

Tom McGuire has done all the work so far. He got a piezo element and hooked it up to the LogoChip. When you strike it, it generates a voltage; he’s working on capturing the voltage in a capacitor until the LogoChip can come along and poll it. The capacitor doesn’t have a drain resistor; he’ll turn the LogoChip port into an output at 0V after he’s read it, to drain it manually. In other words, he’s making a piezoacoustic version of the CCD camera. Brilliant!

Here’s a picture Tom sent of the element attached to a PVC faux bamboo tube:

Tom McGuire's piezo element interfacing


Tom has a few piezo elements, but maybe not enough for the whole instrument (even though Lauren only wants to construct a couple of ranks). But tonight, I mentioned the situation to my friend Joel, and he rooted around to bring out four boards with a dozen piezo elements each, which he’d be happy to donate as long as they don’t all get used up.

Piezo board, back

Each piezo has a rubber-covered button stuck onto the front–Joel thinks they may have come from an ATM or some other heavy-duty input system. It doesn’t feel like they can be removed easily, and I don’t know whether that will prevent them from being useful.

Piezo element, knob on front

Worse, they’re a bit corroded, and trying to remove the silicone that holds down the wire tends to rip the foil right off the back. I don’t know if there’s enough salvageable here or not, but I wanted to post the pictures to let Tom have a look.

Piezo element, back, torn

One I haven’t torn yet:

Piezo element, back

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