Hardware Hacking 21Chapter 7: How to Make a Contact Mike
You will need:
- A battery-powered mini amplifier.
- A Piezo-electric disk (see text below.)
- 8’ lightweight shielded cable.
- Some plugs to match the jacks on the amp.
- Plastic insulating electrical tape.
- A can of “Plasti-Dip” (sold in hardware stores for dipping tool
handles.) - Small spring clamps.
- Molex-style terminal block.
- Hand tools, soldering iron and electrical tape.
- Optional: sparklers, small blowtorch, guitar strings, metal scrap,
Slinky, springs, condoms.
The Piezo-electric Effect
Another common principle of reversible sound translation is the “Piezo-electric
effect,” which depends on the electrical properties of crystals, rather than
electromagnetism: bang a crystal with a hammer and it will generate a pretty
sizeable electrical signal (enough to light a flashlight bulb); send an electrical
current into a crystal and it will twitch. Piezo-electric disks, made by bonding a
thin layer of crystal to thin, flexible sheet of brass, are everywhere today, inside
almost everything that beeps: appliances, phones, toys, computers, etc. Because
they are manufactured in huge quantities they are incredibly cheap, and they
happen to make even better contact microphones than they make speakers.
Drum trigger and commercial contact mikes are often made from Piezo disks and
sold at absurdly marked-up prices.
How to make a Piezo-disk contact mike
Try to find a Piezo-disk that already has wires attached, since soldering
directly to the disc’s surface is infuriatingly difficult. Better yet, get a few disks
in case you break them. You can salvage them from all sorts of trashed electronic
devices, from toys and alarm clocks to cell phones and computers, or buy them
from Radio Shack or any number of web-based “electronic surplus” outlets.
The disk may be encased in a kind of plastic lollipop. If so, carefully pry open
the case and remove the disk. Try not impale yourself, but DO NOT BEND OR
SCRATCH THE DISK!
The disk may have a tiny circuit board attached, Snip off the connecting wires
close to the circuit board, so that the wires attached to the disk are as long as
possible. Remove the board.