PROJECTS: Squishy Tech
quite a bit (Figures
B
and
C
). For our purposes,
we’re looking for items with a range between 500
kilohms (kΩ) and 1 megohm (MΩ).
What’s fun about using food or plant matter, is
that as time progresses you’ll notice the values
change. If you leave your circuit connected, or
try it again every few days, you’ll see the values
usually decrease as the living matter decays.
A 555 AND ATARI PUNK
The 555 timer is an infamous chip, used to make
so many different circuits. One of my favorites is
the Atari Punk circuit, which is basically a really
simple synthesizer made from an oscillator. It's
made from either two individual 555s, or a 556,
which is just two 555s jammed into one neat
package. The first Atari Punk circuit was designed
in 1980 by Forrest Mims who called it a Sound
Synthesizer and later the Stepped Tone Generator
(Figure
D
). It was eventually renamedthe Atari
Punk Console by Kaustic Machines (Figure
E
),
but this circuit has captured the heart of artful
circuit makers everywhere.
How does this clever circuit produce sounds?
We have to understand a few things about
integrated circuits (ICs). ICs have numbered
pins that perform different functions that
allow us to configure the chip, for example this
circuit configures the 555 chip in monostable
multivibrator mode. When we trigger pin 2, pin
7 begins to charge a capacitor. This charging
process sets off a high pulse on pin 3, causing
the capacitor to recharge through an external
resistor. The resistor limits the speed that the
Forrest Mims, Kaustic Machines
B C
D
E
capacitor can recharge, and thus determines
the length of the pulse. The repeating pulse
creates an audible sound through the capacitor
connected to the speaker. By combining two 555
circuits we can create a more complex sound.
In our circuit, the resistor that limits the charge
speed can be replaced by anything we want that
has a resistance within the range we’re looking
for. So why not fruit? Let’s get started!
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