The Art of the Creative Short Circuit

Jan 1, 2003 12:00 AM, By Qubais Reed Ghazala

A Beginner's Guide to Circuit Bending

GENERAL BENDING

Begin by finding some good-sounding battery-powered musical toys, such as keyboards or talking games. You'll find these clogging the isles of many second-hand stores, as well as at flea markets and garage sales. Bring a supply of batteries when you shop—four each of AA, C, and D sizes— so you can try the devices before you buy them.

Open the toy you've selected in order to expose its circuit, but keep the batteries in place. At each end of an alligator-clip test lead, clip a small metal jeweler's screwdriver (see the sidebar “Circuit-Bending Toolkit”). While the circuit is making a noise, and with your safety glasses on, press one of the screwdriver tips to a circuit trace (see the sidebar “Circuit Precautions”). With the other screwdriver tip, touch the various traces while listening for interesting changes in sound. Every time you find an interesting sound, use a marker to note the connections on the board.

Search the board in this way until all possible connections have been tried. Once you're finished, move the stationary tip to another trace and start again. Repeat this procedure until you have searched the entire circuit. Once you have fully explored the circuit and marked the board, you can implement your newly discovered connections using any of the following parts.

Direct wiring/switches. Between each pair of points, solder a wire with a toggle switch in the middle. Next, mount the switch on the case somewhere. Use the simple mini toggle switch known as Single Pole, Single Throw (SPST).

Potentiometer. Add a potentiometer (variable resistor) to the new circuit. That will allow you to adjust the effect in interesting ways. Potentiometers, like nonadjustable common resistors, come in a variety of values and are measured in ohms of resistance. Experiment with different values to learn about their effects.

Potentiometers usually have three soldering points or lugs. Solder your two wires so that one connects to the middle lug and the other to one of the outside lugs. (Which outside lug you choose determines whether you turn the dial clockwise or counterclockwise to initiate the effect. You may need to experiment.)

Capacitors. Try adding capacitors to obtain timbre changes and pulsing effects. But be aware that larger electrolytic capacitors can hold a charge and zap you. Even though you will rarely see these capacitors in the typical instruments you'll bend, you should read up on the subject of capacitors if you're not familiar with them.

Photo resistors. These are light-sensitive cells that have two wire leads. They convert light into electrical resistance and have the same effect on a circuit as a potentiometer. But instead of turning a dial to vary the resistance, you vary the amount of light reaching the photo resistor.

LEDs. In circuit bending, light-emitting diodes (LEDs) are usually used as low-voltage light sources. You may find that an LED will glow or pulse when placed between circuit points. This can serve as a function indicator. For example, an LED wired to the speaker leads may indicate the envelope of the sound by flashing with the intensity of the sound waves. LEDs may also affect the sound of the circuit, depending on where they are connected.

LEDs are “polarized” components; if they don't glow when connected between promising points on a circuit, try reversing the leads. If they still don't glow, there is not enough power available to activate them.

CAUTION: with your goggles on, test an LED's connections very briefly at first. Overpowered LEDs will glow too bright or off-color at first, and may then finally shatter.

Body contacts. Body contact is an interesting part of circuit bending but by no means crucial. Among the countless designers who have used body contact with electronic circuitry are Michel Waisvisz with his Crackle Boxes and Donald Buchla with his capacitance keyboards.

Although I've used the body-contact system on these low-voltage circuits for 35 years without noticeable harm, I'm not about to tell you that it is without risk. (I have been assured by experts that the voltage levels involved are nothing to be concerned about; the flow is minimal and external/dermal.) If, however, the body-contact system scares you, don't do it.

Body contacts are simply metal contacts, such as drawer knobs or finials (threaded brass balls that attach to light fixtures), that are wired to the pair of circuit-bending points. Each of the two circuit points goes to its own body contact. Nothing is wired between them: no switches, no potentiometers, and no sensors. These contacts, when mounted on the instrument's case, are meant to be bridged by the player's body, making him or her a variable human resistor. Vibrato and tremolo are easy to achieve using body contacts, but you might also find contacts that will affect tone and sound and/or sequence triggering.

Before you begin, search the entire circuit with a volt-ohm meter. If you find areas that are more than 6V, avoid them in your body-contact searches. If you ever feel the electricity of a body contact, abandon it or find an alternative.

After verifying a low-voltage board with your volt-ohm meter, search the circuit as before. This time, however, hold a screwdriver in each hand instead of using the alligator-clip test lead (see Fig. 1). While listening for changes in the sound, mark the responsive connections for body contacts. Next, wire a metal object to each point and attach them to the case. By touching these contacts, the player changes the sound and becomes an integral part of the circuit.

Again, it must be stressed that you should attempt the body-contact method only with battery-operated audio devices that use 6V or less. Never attempt this procedure using a device that is plugged in to an AC wall outlet.