After reviewing in class this past Thursday, I learned that capacitive-touch and piezo-based-touch were two completely different things. Oops.. So, I did more research on piezoelectricity and piezo discs (because I already have a few in hand) by researching through a few different websites and YouTube videos. I tried to look in the Art of Electronics to see if I could find anything, but there wasn’t much. I did, however, find the dictionary meaning of piezo. The word is derived from the Greek language to mean “to press” or “to squeeze.”
In general, a bare piezo disc (also called a piezo transducer) is made up of quartz crystals or ceramic material and it is polarized with positve and negative poles. When pressure is applied to the disc, that mechanical energy displaces the quartz or ceramic material, which in turn produces a voltage. In other words, vibrations placed on a piezo will be converted into electrical signals. If more pressure is placed on the piezo, then it will provide higher levels of voltage. There are also two basic types of piezos. One type is to make buzzers or tiny speakers (like the ones that can be heard in some kiddy toys). The other type is to act as a pickup. For example, vibrations from guitar or violin strings (or in my project case, a drum kit or piano keys) will convert into the electrical signals, which then can be wired as an input to produce a MIDI output signal that makes noise (which is another case of my project).
As an introduction to my testing, I ended up buying two piezos (which were both encased at the time of purchase). For one of the discs, I removed all of the black plastic casing (as seen in the picture below). I learned that the plastic acts a mount and cushion to protect the actual piezo because it can be extremely fragile (as seen with my not-so careful, tiny dents). I also found out in one post at this music site that if the casing is preserved, then there will be major feedback in the pickup. I ended up testing both pieces, so it was good thing I had the two.
In a simple test, I took the bare disc and hooked it up to a handheld multimeter to test the voltage. I squeezed on the disc with my bare fingers and although the voltage change looked very minimal, I did see a slight rise in the voltage (from about 510 mV to 0.789 V to 0.924 V). I tried to take a picture of the event, but sadly, I ran out of free hands (and the changes were too quick for me to catch on camera). I tried to do the same on the encased piezo, but it was a little difficult squeezing the black plastic, as well as doing a reading. To actually see a change in voltage (198 mV to 0.276 V to 0.343 V), I ended up tapping and flicking the disc with my fingers. I only remembered after that plastic doesn’t conduct electricity, so I realized how silly this test was. Still, at least I got something out of it…
For the rest of my research, I found a helpful YouTube video on an Arduino xylophone at this site. So far the basic components that I already have are an Arduino Uno, 220 Ω and 100 MΩ resistors, wires, and piezo elements. I still need to get and test inputs and outputs on a female MIDI connector. I also need a 4051 multiplexer IC chip. This will help expand the inputs and outputs on my Arduino Uno, although I could invest in an Arduino Mega in the near future.
As of right now, I’m in the “waiting for parts to arrive so I can test them and I hope I stay positive through all of this” stage. In the meanwhile, I hope I’ll survive inventory time at the BFC because it’s coming up soon. Bead strands mixed with school work have never felt so overwhelming… :[