68 Nicolas Collins
Similarly, if you wire a pot in series with a photocell, you can use the pot to set
the upper pitch limit of a light-control instrument, combining the best of two
worlds: the accurate control of the pot and gestural freedom and expressiveness
of the photocell.
- You can also use bare wires (with or without dimes soldered to the ends) to
make a “laying of hands” oscillator , like our radio and toy experiments, or the
infamous STEIM “Kracklebox.” Substitute the electrodes for the resistor or pot by
connecting one to the inverter’s input and one to its output; if you connect the
electrodes in parallel to a pot (as discussed in Chapter 15) you can use both
elements to control the pitch. Experiment with alternate types of resistors.
Why? (If you care.)
In case you wonder, this circuit oscillates because of the principle of
argumentation. Each inverter stage, represented by the small triangle in the
schematic, puts out the opposite of whatever signal appears at the input: if a
binary “1”, represented by 9 volts, is applied to the input, then a “0” (0 volts) is
sent to the output. That 0 flows through the resistor back to the input. When the
0 appears at the input the output goes to 1, which flows back to the input and the
whole process begins again, causing the circuit to flip back and forth between
two states, generating a square wave. The speed of the flip-flopping (the pitch
we hear) depends on the values of the resistor and capacitor -- just like in our
earlier clock experiments, the smaller the values the higher the pitch. It’s like the
Monty Python argument sketch: I disagree with everything you say, so our
output keeps flipping between yes and no according to how fast each of us can
reply. The resistor and capacitor act like booze – the more you add the slower
the argument goes, ergo the lower the pitch.
Polyphony
As you might be able to tell from the schematic, the Hex Inverter has six identical
sections. You can make an oscillator circuit with any stage -- just duplicate the
connections we made for our first oscillator with another set of components,
attached to another set of pins: capacitor between any input and ground; resistor,
pot, or photocell between that input and its appropriate output; connect the