Piezoelectric Sensor
From Physical Programming
Contents |
Piezoelectric Sensors
The piezoelectric effect can be used to sense when there is a change in stress upon a surface or within a material. It can therefor be used to detect a wide variety of inputs.
Applications
Piezoelectric disks are extremely versatile sensors in that they can be used to detect human interaction (through squeezing, pressing, tapping and so on) or to detect a frequency resonating on a surface (such as the body of a guitar, a snare head, or a metal girder in a bridge). The piezoelectric effect is also reversible, meaning that it can input and output fluctuations, for example it can function as a recording device [1] or a playback device [2]. There is also research being done into anti-vibration technology whereby the piezoelectric effect is used to detect vibrations in a material and then create a counter-vibration that cancels out the original vibration. This would have interesting applications in power tools, computers, vehicles and other machinery. Perhaps a tray in the interior of a tractor that you can rest a beer on without it foaming up.
How They Work
The piezoelectric effect is observed within certain crystals, ceramics, bones and other materials. When pressure is applied to a piezoelectric material it generates a (potentially very high) voltage.
Everyone would have witnessed this using a gas stove, or BBQ lighter. The "click" that is heard when using a BBQ lighter is a spring-loaded hammer hitting a piezoelectric surface, creating a voltage which jumps between two wires in the form of a spark, igniting the gas so that we can cook food [3].
Arduino Interaction
An existing project (found at hackedgadgets.com) is a Laser Cut Piezo Drum Kit [4], which uses piezoelectric disks to act as triggers which the Arduino interprets into MIDI values (with the help of another board [5]). This means that you could record and play a beat once - and because it is in MIDI format - play it back using different drum sounds, or remove or add notes to the beat. The beauty of this project is that an average electronic drum kit is well over $1,000 to purchase.
Using an Arduino to interpret the voltages (signal) that a piezoelectric disk creates offers up a wide variety of applications. Having a piezoelectric disk on the body of an acoustic guitar for instance you could then use a program to track the frequency (pitch) of the melody being played. Then by outputting that frequency using an oscillator you could create a rudimentary harmoniser.
A harmoniser could be interesting in the form of a Singing Bowl (or Tibetan bowl), which is basically a musical instrument in that it vibrates to produce sound. Singing bowls are used for meditation, trance induction and prayer. I'm not sure if it would be possible for me to track the frequency of the bowl because the Singing Bowl is a multi-phonic instrument, which creates complex overtones. However I could possibly reinterpret the sound visually, through LED's.
