Physical interaction design DH2400

Piezoelectricity is the ability of some materials to generate electricity in response to a mechanical constraint. It's called the direct piezoelectric effect, and the reverse piezoeletric effect is a strain of the material when an electric field is applied to it. They are many applications of this effect, and two very famous one are the lighter (or push-start for propane installations) and the quartz cristal in our watches (to generate the clock impulses).
So, the piezo electric sensors we use can detect both vibrations and direct taps by generating a proporitonal electric current. That's why there main application is around electronic drums and "tapping systems" in a broad sense but as we discovered here for our FluffyTable, they can quite easily detect also strokes (given with enought pressure).


One of their main advantage is to be very cheap (around 10kr each), and they exist in different sizes (from around Ø10mm to Ø35mm on elfa). They are quite reliable even if some sensors can be more sensitive than others from the same size (the way they are fixed is also important). It was ok for us because we just needed an activation value. Connected with a basic 220kΩ they return values between 0 and 400 that is completely enough to compare inputs.


Here is a basic drum application done with an Arduino and four piezo sensors: