Music may be an art, but making it sound its best is a science. There are many ways to produce music using both analog and digital methods, and the capacitor is one of the most critical components involved in electronic audio. Capacitors can filter out specific frequencies, they can tune a radio, and when combined with a 556 dual timer chip (or two 555s), they can create a very simple and versatile instrument.
Fig 1: Simplified Stepped Tone Generator
This instrument, called a “Stepped Tone Generator,” was designed by Forrest M. Mims III and published in the 1980s. Mims’ design outputs sound signals directly to a speaker, and engineers have tweaked this simple design in countless ways, including the line-level “Atari Punk Console,” commonly used with powered speakers.
The name Atari Punk Console references the results of this build, which sound like a 1980s arcade game with their distinct bloops, bleeps, and hums. Controls consist of two potentiometer knobs: one varies the sound frequency and the other controls the width of each generated square wave.
Build your own Stepped Tone Generator using the parts list and instructions below.
We’ve outlined a simplified version of Mims’ circuit, omitting the volume potentiometer and using a pair of CR2032 coin cell batteries to save space. We subbed 200k potentiometers for the 1M pots originally used. The parts list for this build is fairly simple, with components that are easy to find in a well-stocked shop:
(1) 556 timer chip (or 2 555 timers)
(2) .1μF capacitors
(1) 10μF capacitor
(2) 200 kOhm potentiometers
(1) 1K resistor
(1) 8 Ohm speaker
(2) CR2032 coin cell batteries and (1) holder
Hookup Wires (single strand 22 gauge recommended)
With those parts in hand, all that’s left to do is connect the circuit as diagrammed in the image below. We recommend single-strand wire that you connect and clip to the correct length. Without clipping the wire, you’ll have a barely-visible 556 timer surrounded by a forest—pardon the pun—of unintelligible hookup wires.
Fig 2: Simplified Stepped Tone Generator Layout. Capacitor connected to speaker is 10μF, others are .1μF.
This modified version shows how versatile Mims’ circuit is, and you can experiment further with different capacitor and potentiometer values. Add on to the circuit by chaining more components to its output, or by interfacing a microcontroller to change things further. You can even hook an oscilloscope to the output to see how the waveform varies as you twist the knobs.
Fig 3: An oscilloscope can help visualize what is going on with your new instrument.
Building a Stepped Tone Generator is a fun experiment. Hearing the funky retro sounds of arcades of old is a great payoff to a correctly built circuit. While you could use a microcontroller to obtain a similar effect, this circuit is an approachable, useful introduction to both capacitors and the incredibly popular 555 and 556 integrated circuit.