by Forrest M. Mims III


The Mystery Component is a piece of black conductive foam plastic like that used to store CMOS and other components that are sensitive to electrostatic discharge.


How It Works

Figure 2 shows the circuit with the two input leads inserted into a piece of conductive foam plastic. For test purposes, insert the two wires directly into opposite sides of conductive plastic. Pressing down on the foam plastic reduces its resistance and increases the frequency of the tone emitted by the speaker.



Figure 2. The mystery component in Figure 1 is conductive foam plastic.


Background

Many different resistive sensors can be used to alter the frequency of a tone emitted by a 555 pulse generator. This method is certainly one of the simplest--and it allows electronic musician Joe Rhythm to control the tone frequency with a spare finger or even an elbow.

Going Further

For practical use, build a sturdy version of the sensor by sandwiching the conductive foam between two pieces of copper-clad PC board or other conductive surface to which wires can be soldered or attached. Hold the sandwich together with nylon 2-56 screws and nuts.

About the Author

Forrest M. Mims III has been an electronics and science writer and photographer since 1969. He received an IR 100 Award from Industrial Research Magazine for developing an eyeglass-mounted infrared travel aid for the blind. He received a Rolex Award in 1993 for developing a handheld instrument that measured the ozone layer accurately enough to find an error in a NASA ozone satellite. He was named by Discover Magazine (December 2008) as one of the "50 Best Brains in Science." See his home page and publications here and follow him on Twitter.