PHYS341/2024/Project15
Atari Punk Console
The Atari Punk Console (APC) is a simple analogue music synthesizer that can be built using basic electronic circuit materials. Its popularity stems from its ease of building and simplistic schematic, making it a great starting point for beginners to learn about analogue synthesizers. This article delves into the background of the synthesizer and its physics, highlighting the parallels between music and electronics.
Background
The Atari Punk Console was created by Forrest Nims and published in his 1984 book, Engineer's Mini-Notebook: 555 Circuits. It was later retitled as the "Atari Punk Console" due to its video game-like sounds. The synthesizer creates its sound by using electrical oscillation, which is later converted to sound through a small speaker. The electrical oscillation produced within the synthesizer is a change of voltage, otherwise known as the difference in electric potential. This difference in electric potential is what allows electricity to flow through the synthesizer. Thus, this alternating voltage also produces an alternating electric current that is proportional to the voltage controlling it. In the electronics circle, the APC is accordingly categorized as a voltage-controlled oscillator, or VCO. As a VCO, the APC produces a square/pulse wave. This wave is a representative of repeated instantaneous changes in voltage over time.
Components
The synthesizer is made up of many basic electronic materials. This section introduces these materials and the physics of their electronic components. The materials for an Atari Punk Synthesizer are as follows:
Breadboard
A breadboard is the base for basic/temporary circuits. It is the medium that connects the individual components of a circuit. On the surface, breadboards appear to only be made of plastic. This plastic has several holes on the top surface, where equipment can be connected to make a circuit.
The columns marked as power rails and rows marked as terminal rails are where the power supply is connected. Connecting the power supply to a positive and negative rail creates a difference in potential that allows electricity to move through the circuit. The metal strips hidden under the plastic of the breadboard conduct electricity and allow an electric current to run through the terminal rails where you build your circuit. Without them, the circuit won't work.
Note that the APC can be made via other methods, but for this project we will stick to using a breadboard.
Battery
A battery provides voltage to a circuit. It does this through two terminals, the positive terminal and the negative terminal. The positive terminal has a higher potential, while the negative terminal has a lower potential. For clarification, the difference in potential between these two terminals is the voltage. This voltage causes electric charge to flow throughout the circuit.
Resistor
A resistor decreases voltage, which can decrease the electric current that will flow. As an analogy, it is useful to think of a resistor similar to how a thin water pipe will slow the flow of water current. In terms of our APC, we can use resistors to slow down voltage and current, which thus slows down the oscillations produced.
Potentiometer
A potentiometer is a kind of variable resistor, meaning that it can change its resistance value. Potentiometers do this with a knob, three terminals and an internal resistive material. Inside the potentiometer, the two outer terminals are connected to the resistive material, while the middle terminal is connected to the adjustable knob. Externally, one outer terminal and the middle terminal are connected to the circuit, meaning that there is a voltage drop across these two terminals. As the knob is turned, the amount of resistance material between the wired middle terminal and outer terminal is increased/decreased accordingly.
Capacitor
A capacitor is made of two conducting plates that are isolated from each other. When connected to a voltage, current builds on one of these plates, repelling the like charges on the opposite plate. After a long time. both plates end up being charged with a maximum equal and opposite charge. However, when removed from voltage, the plates begin to discharge. Essentially, a capacitor acts like a balloon that fills up with electric charge and then releases it all when there’s no more charge being supplied. How much charge it can hold depends on the geometry and material of the capacitor.
555 Timer
Overall, the 555 timer serves to produce a "pulse." The timer is an integrated circuit (IC) chip with 8 separate pins, with each pin serving a different purpose. Pins 1 and 8 connect the timer to the voltage. Pin 1 is connected to "GND", or ground, which refers to the negative power rail of the breadboard. Pin 8 is connected to "VCC", or common collector voltage, which refers to the positive power rail of the breadboard. Pin 2 acts as the trigger, activating the pulse when it receives a voltage greater than 1/3 of VCC, and the output is on pin 3. Pin 5 controls the timing of the pulse, pin 6 sets the threshold to turn off the output when the voltage exceeds 2/3 of VCC, and pin 7 assists in discharging any capacitor used in timing to GND. It is important to note here that once a 555 is triggered, it will ignore all other triggers until it completes its output.
How the circuit works
The Atari Punk Console is A VCO that produces a square wave or pulse wave. This wave is a change of voltage over time, which is produced from the two 555 timer pins.
Both of the 555 timers are wired in a different setting, or state. The first timer is wired in an “astable” state, while the other is wired in a “monostable” state. Both timers work in conjunction with a capacitor and potentiometer.
In the astable state, the first 555 timer goes switches between an "on" and "off' state. Both of these states are considered unstable, as the switches are abrupt and not from an external signal. The astable 555 timer pulses from on and off at a rate controlled by a potentiometer. In other words, by changing the resistance of the potentiometer, you can change the pulse frequency produced by the first timer. The resulting wave is not the final product and must go through the second 555 timer to produce the well-known sound from the APC.
The monostable timer receives the first pulse and then outputs another at a duration that is controlled by another potentiometer. The timer switches from on and off, however the nature of these switches comes from two sources: the output of the first timer (stable) and the potentiometer/capacitor it is wired to (unstable.) It is important to note here that this output has the same frequency as the first, as the monostable has no control over the frequency of its pulse. In terms of the waveform, this state controls the duty cycle - this is the ratio of the length of the on state versus the length of the off state. (Fun fact: a square wave is just a pulse wave with a 1:1 duty cycle.) By controlling the duty cycle, you can adjust the width of the pulse.
The output from the second timer is then sent to a speaker, where the electrical signal is converted into a sound wave.
Effect of potentiometers on sound wave
The APC has two potentiometers that control the pulse width and duty cycle of the pulse wave produced. We'll examine their effect on the sound wave by looking at waveform screenshots from an oscilloscope [1], as square waves are easily distorted/ignored by microphones.
When changing the resistance of the first potentiometer, the frequency of pulses shifts. This affects the pitch of the final APC output. Electronically, this is because the first timer then sends a trigger to the second at a higher/slower rate, affecting the number of pulses the second timer emits per second.
When altering the resistance of the second potentiometer, the duty cycle shifts. This affects the overall timbre produced. For example, with a low-duty cycle, the final output of the APC sounds much more tinny. As you begin increasing resistance and the duty cycle, the square wave begins to sound more rich. This is because, as a waveform, a smaller pulse width includes less of the lower and bassier harmonics, which leaves the higher harmonics untouched.
By adjusting the potentiometers, you can create retro "Atari"-like sounds. Interestingly, due to the nature of the 555 timer chip, increasing the frequency while maintaining a high-duty cycle can cause the pitch to drop unexpectedly and then increase again. This is because the chip ignores all other triggers until it completes its output. As the second timer chip receives more pulses per second while maintaining its high-duty cycle, it will eventually ignore the increase of trigger pulses. This causes the pitch to drop significantly before starting to increase again.
References
- BrownDogGadgets, & Instructables. (2017, October 30). Build an Atari punk circuit on a Breadboard. Instructables. https://www.instructables.com/Build-an-Atari-Punk-circuit-on-a-breadboard/
- Dave. (2011, December 21). Atari punk console - how it works. Notes and Volts. https://www.notesandvolts.com/2011/12/atari-punk-console-how-it-works.html
- Halliday, & Resnick. (2021). 25, 26, 27. In Fundamentals of Physics 12th edition. Wiley Plus.
- Hewes, J. (2008). 555 and 556 Timer Circuits. The Electronics Club. https://k1.spdns.de/Develop/Hardware/Circuits/555%20Timer%20Circuits/
- Lewis, K. (2019, March 2). How to wire a variable resistor. https://sciencing.com/how-to-wire-a-variable-resistor-12176736.html
- Orchard, L. (2020, August 17). Atari punk console on an oscilloscope. YouTube. https://www.youtube.com/watch?v=hEpF10zIDUY
- Randofo, & Instructables. (2022, November 15). Atari punk console synthesizer. Instructables. https://www.instructables.com/Atari-Punk-Console-Synthesizer/
- Storr, W. (2022, August 3). Multivibrators including monostable, Astable and bistable. Basic Electronics Tutorials. https://www.electronics-tutorials.ws/sequential/seq_3.html
In-text citations:
- ↑ Orchard, Les (August 16, 2020). "Atari punk console on an oscilloscope".