Circuitry-Based Sound

Group live performance at the ZKM

"Circuitry-Based Sound" is an artistic workshop at the intersection of electronic music, sound art, and performance, exploring the low-threshold use of analog sound technologies in structured improvisation, experimental music, and live electronics. The course provides hands-on skills for building custom musical circuits and modifying existing audio hardware, offering practical knowledge of electronics for sound creation and DIY instrument design.

The workshop covers basic electronics, soldering, and assembling circuits on breadboards and perfboards, as well as their applications in audio composition and installation art. A major focus is on hardware prototyping, including testing, fault finding, and designing electronic instruments, with an emphasis on musical interaction through experimental interfaces and haptic controllers.

Beyond the technical aspects, the project explores the performative and aesthetic potential of self-built audio circuits, enabling collaborative music-making in concert settings.

Below is a documentation of the workshop’s study materials and findings.

TABLE OF CONTENTS

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INTRODUCTION

• Unconventional Electronic Sound
• CMOS Chips for Sound Creation
• Basic Example
• Logic Control
• Building Circuits with Breadboards
• Identifying IC Pins

ELECTRONIC COMPONENTS

• Numerical Index

BASIC PRINCIPLES AND APPLICATIONS

• Signal Mixing
• Passive Filters
• Potentiometers
• LDRs (light-dependent resistors)
• Pull-up and Pull-down Resistors

EXPLORATORY SOUND CIRCUITS

• Linear Feedback Shift Register
• Step Sequencer
• Melody Generator
• Voltage Starve

MATERIALS

• Requirements
• Bill of Materials
• Artists
• Acknowledgment
• Literature
• Links
• License

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Disclaimer

The authors accept no responsibility for any damages arising from or in connection with the use of the information provided on this website. While we strive to ensure that all content is accurate and complete, unintended errors may occur. Users are encouraged to cross-check and verify the information before applying it.

Introduction

Photo: Yunfei Zhang

Aside from the conventional use of electronics in analog synthesizers to generate and process sound, there are also unconventional applications for creating experimental music and sound, which will be introduced below. Analog synthesizers typically employ techniques like subtractive synthesis, where an oscillator’s output is filtered and dynamically shaped in volume. Variations of this concept are found in most synthesizers, both analog and digital. Hardware-based analog modular synthesizers are highly valued for their distinctive sound and, in particular, for their voltage-controlled compositional flexibility and immediate, tactile sound manipulation. However, achieving these functionalities, especially when building analog circuits for modular synthesizers, requires relatively complex circuits, a high component count, and precision parts.

Unconventional Electronic Sound

Another approach to electronic sound creation emerges from hardware hacking and circuit bending techniques. In particular, the use of logic circuits beyond their conventional applications presents a compelling method for building customized instruments for artistic sound production and interactive music. These components are inexpensive, widely available, and require minimal external circuitry, making them highly accessible for DIY experimentation. Their ability to generate and process sound with minimal wiring and low cost makes them a powerful tool for unconventional electronic music.

CMOS Chips for Sound Creation

Various CMOS chips

CMOS chips are designed to execute Boolean functions. The development of electronic circuits capable of performing logical functions was a major milestone in the history of computers. Complementary metal–oxide–semiconductor (CMOS) technology utilizes p-type and n-type MOSFETs to construct logic gates, where voltage levels represent binary states (0 and 1). A Boolean function is a logical expression that maps one or more binary inputs (0 and 1) to a single binary output. Produced as integrated circuits, individual CMOS components implement basic logic functions such as NOT, AND, OR, NAND, XOR, XNOR. More complex chips provide functions like multiplexers, counters, dividers, flip-flops and registers.

A binary logic signal, which encodes 0 and 1 as two distinct voltage levels, can be represented as a square wave. A logic signal that continuously switches between these two voltage states can therefore be interpreted as a square wave—and thus as sound.

The following diagram illustrates the waveform of a square wave and assigns the values 0 and 1 to its two voltage states.

When the relationship between logic operations, voltage, and sound is understood, CMOS logic chips become an inexhaustible resource for unconventional electronic sound. These chips generate square waves that can be modified, shaped, gated, sequenced, and layered. By combining different logic functions, they enable the creation of a vast range of unique sounds and temporal musical structures, while still retaining the richness of analog sound. Additionally, these circuits often exhibit unpredictable behavior, producing rhythmic glitches, digital noise, and evolving textures, making them an essential tool for experimental sound design.

Logical operations can be implemented as switching circuits, where single-pole single-throw (SPST) switches represent inputs, and an LED indicates the output result. Both the switch and the LED have two distinct states: on and off.

• An open switch corresponds to logical 0, while a closed switch represents logical 1.
• A lit LED indicates 1, whereas an unlit LED represents 0.

A truth table is used in Boolean algebra to display all possible input and output values of a logical expression.

Output comparison of 2-input logic gates:

INPUT A	INPUT B	AND	NAND	OR	NOR	XOR	XNOR
0	0	0	1	0	1	0	1
0	1	0	1	1	0	1	0
1	0	0	1	1	0	1	0
1	1	1	0	1	0	0	1

Due to their simplicity and accessibility, CMOS chips are widely used for artistic and educational purposes, as their technical operations are easy to understand and closely related to basic electronics concepts. This topic has been explored in various publications, most notably in Nicolas Collins' Handmade Electronic Music: The Art of Hardware Hacking (2006). American composer David Tudor (1926–1996) is regarded as a pioneer of self-built electronic circuits and instruments, which he integrated into his compositions. Similarly, avant-garde composer and artist Stanley Lunetta (1937–2016) began incorporating digital electronics into his compositions and sound art sculptures in the 1970s, sharing his techniques with fellow artists. As a result, in the experimental music community, CMOS-based synthesizers are often referred to as “Lunettas”, honoring Lunetta’s contributions to DIY electronic music.

Basic Example

The “Hello World” of CMOS synthesizers, illustrating how easily sound can be generated, is shown in the diagram above. It depicts a square wave sound generator that requires only three components, jumper wires, and a power supply:

• An inverting Schmitt trigger IC (e.g., CD40106)
• A capacitor (C)
• A resistor (R)

An inverting Schmitt trigger is an active electronic component whose output state toggles complementarily in response to an input signal, with distinct positive and negative trigger thresholds—a property known as hysteresis. By feeding the output back to the input via a resistor (R) and connecting a capacitor (C) between the input and ground, a circuit known as an RC oscillator is formed. This configuration, commonly referred to as a relaxation oscillator or astable multivibrator, generates a continuous square wave signal. The resistor limits the charging current, while the capacitor and resistor together determine the RC time constant, which sets the oscillator's frequency.

The frequency can be roughly calculated with this formula

$$f=\dfrac{1}{T}=\dfrac{1}{RC ln [(\dfrac{V_P}{V_N})(\dfrac{V_{DD}-V_N}{V_{DD}-V_P})]}$$

where V_P is the positive trigger threshold voltage and V_N the negative trigger threshold voltage.

However, manufacturing tolerances of all involved parts make it difficult to achieve exact results based on the formula. Since the field of application is artistic sound production, circuits should be evaluated by ear. But the formula shows that bigger RC values produce lower frequencies and vice versa. The frequency is determined through the capacitor C and the resistor R. Therefore, a potentiometer instead of the latter enables pitch control. Other ways of controlling the frequency may be inserting photoresistors, force-sensitive resistors (FSR) or flex sensors. Adding circuit points to alter the sound through interaction allows building customized and versatile instruments.

Logic Control

In digital electronics, binary code is represented by two defined voltage levels that are specified by the used technology and circuit. Everything below a certain voltage threshold level is recognized as 0 and everything above a certain threshold level is recognized as 1. A voltage level in between the two thresholds is not defined or forbidden and will produce false output triggers. CMOS digital inputs have a high impedance and pick up thermal noise voltages if left floating. Unused inputs should be tied to a defined voltage. Other input configurations (e.g. taster, toggle switches,) require pull-up or pull-down resistors. The two states "0" and "1" are also often referred to as "(logical) high" and "(logical) low", "true" and "false" or "ON" and "OFF".

V_IH is the minimum input voltage that will be interpreted as a logical high, while V_IL is the maximum input voltage that will be interpreted as a logical low. The region in between is undefined and may trigger unpredictable highs or lows (chattering). This problem is solved by implementing a Schmitt trigger with different thresholds for negative-going and positive-going input voltages, depending on whether the input signal is changing from high to low (V_N) or low to high (V_P). When the input is between the two thresholds the output retains its value.

A logic gate is a single input - output device, designed to carry out a specific Boolean operation, mapped to two voltage levels. Over time, the two alternating voltage levels may form a periodic rectangular waveform and the speed of switching between the two levels is perceived as pitch. Certain logic gates can be repurposed as oscillators in this way. In digital systems, this principle is used to generate clock signals, which are essential for synchronizing processes. Logic gates with two inputs compare the signals at their inputs and generate an output based on the corresponding logic function, enabling signal processing and modification. Other logic gates can count sequential square wave pulses, outputting a single pulse per cycle. Some function as frequency dividers, halving the input signal’s frequency. Additionally, various CMOS chips can act as binary-controlled switches. These and many other functions can be considered as modulation effects, which transform or modify the incoming audio signal.

Aperiodic switching will produce other sonic qualities such as noise or all kinds of texturized sounds. The ratio between the on- and off-states is by default close to 1:1, a 50% duty cycle. Further circuitry is needed to change this ratio, which alters the ratio of the amplitudes of the harmonic components to the fundamental. The square wave contains only overtones with odd numbered harmonics (⅓, ⅕, ⅐, etc). The relative amplitudes of the harmonics are equal to 1/harmonic number n.

Building Circuits with Breadboards

Since assembling an electronic circuit on a breadboard does not require soldering (unlike working with printed circuit boards) it allows for quick prototyping and easy modifications. This makes breadboards particularly useful for testing and developing preliminary functional versions of circuit designs, which can then be used to verify circuit behavior and operating points. They serve as temporary platforms for functional verification and feasibility testing, while their flexibility and reusability make troubleshooting easier.

Typically, circuits built on breadboards are not suitable as permanent solutions, as the connections rely solely on spring contacts. These contacts can corrode over time or become loose, leading to unreliable connections. This is especially problematic during transport, as components may detach.

Nevertheless, breadboards are highly effective for DIY electronic music projects, as they allow for rapid prototyping and easy circuit adjustments to match sonic preferences. They can also be expanded with control elements, enabling intuitive sound manipulation and music interaction.

Breadboards are made of plastic and feature a standardized hole grid with metal spring contacts. The grid spacing is 2.54 mm (0.1 inch), making it compatible with most standard electronic components and allowing for easy insertion and interconnection.

A typical breadboard consists of three main sections:

• Power Rails: Located along the outer edges, these two continuous strips are internally connected and typically used to distribute power across the board (usually indicated with the symbols + and - and/or the colors red and blue).
• DIP Support: A central gap that separates the two sides of the breadboard, designed to accommodate dual in-line package (DIP) components, such as integrated circuits (ICs).
• Terminal Strips: Arranged perpendicularly to the power rails, these rows of interconnected holes on either side of the centerline provide access to the pins of DIP components, enabling circuit connections.

In most circuits, the majority of connections go to ground or a supply voltage. For convenience, it’s best to connect the power rails on both sides of the breadboard so you can easily access ground or the supply at any point across the entire board.

Identifying IC Pins

Manufacturers provide documentation for integrated circuits (ICs) and other electronic components in so-called datasheets, which describe the components' characteristics and functions. In an IC datasheet, the pinout diagram explains the function of each pin (or terminal) while also providing important information about operating conditions and supply voltage. When using ICs, it is important and highly recommended to have the datasheet readily available to ensure proper implementation of the component.

Illustration of an integrated circuit (IC) and a detailed view of one functional block from its internal circuitry

For Dual In-Line Packages (DIL or DIP ICs), the pins are numbered sequentially. When looking at a DIP IC from above, there is typically a marking or notch on one of the shorter sides of the package, which serves as an orientation guide.

To correctly identify the pin numbering:

• Align the IC so that the notch or marking is at the top.
• Start counting from the first pin on the left side of the notch (Pin 1).
• Continue numbering counterclockwise around the IC.

This standard numbering convention helps ensure correct connections when integrating the IC into a circuit.

Most CMOS chips have 14 or 16 pins. With only few exceptions (e.g., CD4049UB and CD4050B), the bottom-left pin is typically connected to ground (GND or Vss), while the top-right pin (the last pin) is connected to the positive supply voltage (VDD).

Electronic Components

The following is a list of CMOS chips and other integrated circuits used for sound creation and processing. This list will be continuously expanded throughout the seminar. Each chip’s primary applications are outlined, along with a brief explanation. Pinouts, functional diagrams, truth tables, and basic example circuits are also provided. However, these examples do not represent a comprehensive guide. The main objective is to explore variations, modifications, and new creative combinations for experimental sound and music. For detailed specifications, please refer to the manufacturer’s datasheet.

Numerical Index

• CD40106
• CD4093
• CD4070
• CD4015
• CD4022
• CD4040
• CD4046
• CD405x
• CD4066
• CD4060
• CD4013
• CD4018
• 555 Timer
• LM386

CD40106

The inverter is a fundamental component in digital electronics, performing the logic operation of negation. When the input is connected to ground, the output is pulled to V_DD, and vice versa. The CD40106 Hex Schmitt Trigger Inverter contains six independent inverters in a single chip. Unlike standard inverters, its Schmitt trigger action provides hysteresis, allowing for unrestricted rise and fall times on the input, which makes it especially robust against noise. This chip can be externally wired to function as one or more square-wave oscillators (see illustration).

When using a potentiometer for frequency control, add a series resistor to avoid an excessively low-resistance path between the output and input, which can disrupt proper operation and force the oscillator to remain at high frequencies—even beyond the audible range.

Applications:

• Square Wave Generator
• Inverting Buffer

Truth table for NOT

Inputs	Outputs
0	1
1	0

"1" = High Level
"0" = Low Level

CD40106 Sheet

CD4093

The CD4093 contains four NAND Schmitt triggers, each with two inputs and one output. When configured as an inverter, it can function as a square wave oscillator. The last two rows of the truth table show that one input must be set to a logical high for the gate to act as an inverter, allowing the second input to control the output. By wiring one input like the CD40106 oscillator in the previous example and keeping the other input high, the CD4093 can also generate square waves.

Applications:

• Square Wave Generator
• Gated Oscillator

Oscillators built with 2-input NAND Schmitt triggers can be manually switched on and off using a push button. When the push button is not pressed (normally open), the logical low at the second input forces the output high, regardless of the state of the first input (see NAND truth table). The image above illustrates how to configure a normally open push button as an ON switch to control the sound. A pull down resistor ensures the input remains at a defined logic low when the push button is open. When the push button is closed, the power supply applies a logical high, allowing the NAND gate to oscillate. In this setup, the second input serves as a control input for gating the oscillator. Instead of a manually operated push button, a logic signal can be applied to the second input for automated control.

Truth table for NAND

A	B	J=A NAND B
0	0	1
0	1	1
1	0	1
1	1	0

CD4093 Data Sheet

CD4070

The CD4070 contains four Exclusive-OR (XOR) logic gates, each with two inputs and one output. The output is high (1) when only one of the inputs is high, and low (0) when both inputs are either high or low. When two square wave signals are applied to the inputs, the XOR gate acts as a frequency mixer, producing an output that represents the difference between the input signals. This creates a rich, harmonically altered waveform useful in sound synthesis. The CD4070 can also be used for frequency doubling by applying a single square wave directly to one input and feeding it to the second input through a resistor, with a capacitor to ground. In this configuration, the output is driven high on both the rising and falling edges of the input waveform, effectively doubling the frequency. The pulse width of the output depends on the resistor-capacitor (RC) time constant and is shorter than the original square wave cycle. However, when shifting a tone up by an octave using this method, the perceived effect may only be musically satisfying within a limited range of component values.

CD4077 is the Exclusive-NOR version.

Applications:

• Digital Frequency Mixer
• Frequency Doubler

Truth table for XOR (CD4070)

A	B	Y = A XOR B
0	0	0
0	1	1
1	0	1
1	1	0

CD4070 Data Sheet

CD4015

CD4015 IC consists of two four stage shift registers.

The CD4015 is an integrated circuit containing two independent 4-stage shift registers. A shift register is a series of interconnected flip-flops, which are bistable multivibrators capable of storing binary states (0 or 1). Each flip-flop stores one bit of data, and its state is controlled by a clock signal. On each clock pulse, the stored data shifts from one flip-flop to the next. In the CD4015, serial input data (D) is shifted through the register stages and appears at the parallel outputs (Qn), synchronized with the rising edge of the clock signal (CL). When a bit is stored in the first flip-flop, it moves sequentially through the register stages with each clock cycle. A logical high at the reset pin clears all stored values, setting the outputs to zero. To enable continuous operation, the reset pin should be kept low.

Applications:

• Sequencer
• Noise Generator
• Linear-feedback Shift Register (LFSR)

Truth table for four stage shift register

CL	D	R	Q1	Qn
/	0	0	0	Qn-1
/	1	0	1	Qn-1
⧹	X	0	Q1	Qn
X	X	1	0	0

X = Don't Care Case
/ = Rising Edge
⧹ = Falling Edge

CD4015 Data Sheet

CD4022

The CD4022 and CD4017 are counter/divider ICs, with the CD4022 providing 8 outputs and the CD4017 providing 10 outputs. These chips increment their output sequentially on the rising edge of an incoming clock signal. The "carry out" pin generates a pulse once every 8 clock cycles (CD4022) or 10 clock cycles (CD4017), making it useful for cascading multiple counters. A logical high at the "clock inhibit" pin pauses the counting process, preventing further increments. Similarly, a logical high at the "reset" pin resets the counter, setting it back to the first output stage.

Applications:

• Sequencer
• Staircase Wave Form Generator
• Wave Shaper

CD4022 Data Sheet

CD4040

The CD4040, CD4020, and CD4024 are binary counter/divider ICs that perform frequency division. The CD4040 and CD4020 provide 12 outputs, while the CD4024 has 7 outputs. The CD4020 is a 14-stage counter, but its divide-by-4 and divide-by-8 outputs (stages 2 and 3) are not accessible. The CD4024 also has three pins with no internal connection (pins 8, 10, and 13).

When a square wave clock signal is applied to the input, each output generates a square wave at half the frequency of the preceding stage. The first output (Q1) oscillates at half the input frequency, Q2 at one-quarter, Q3 at one-eighth, Q4 at one-sixteenth, and so on. This makes these ICs useful for octave division, subharmonic generation, and frequency scaling. Multiple counters can be cascaded for extended division.

The "reset" pin sets all outputs low (0) when activated. For continuous frequency division, it should be kept at a logical low state.

Applications:

• Frequency Divider
• Sub Octave Generator
• Representation of Binary Numbers

For sound generation with square waves, each output produces a frequency one octave lower than the previous stage, with the input serving as the highest frequency reference.

The timing diagram below illustrates the voltage relationships between all outputs of the CD4024, the 7-stage version of this counter/divider IC:

CD4040 Data Sheet

CD4046

Phase locked loop

Applications:

• Tone Distortion
• Pitch Tracking
• Frequency Multiplication
• Voltage Controlled Square Wave Generator

CD4046 Data Sheet

CD405x

The CD405x series consists of CMOS analog switches available in a 16-pin DIP package, commonly used for switching and routing both analog and digital signals.

The on-resistance (R_ON) of these switches depends on the input voltage, power supply voltage, and temperature. For CD405x devices, this resistance typically ranges from 120Ω to over 200Ω, which may cause some signal distortion in certain applications. However, for the purposes of this project, this resistance is generally low enough to be negligible.

Key Functional Notes:

• Unused control pins must be connected to either GND or V_DD to prevent floating inputs.
• Inhibit input (active low): When set high, all channels are switched off.
• V_EE (Pin 7) is used for dual-supply operation. In single-supply mode, it should be tied to ground.

Applications:

• Wave Shaper
• Digitally-controlled Analog Switching
• Signal Routing
• controlling LEDs

CD4051

The CD4051 is an analog switch configured as a single-pole, 8-throw (SP8T) multiplexer with three binary control inputs for selecting the active channel.

Truth table for the CD4051

INHIBIT	C	B	A	ON CHANNEL(S)
0	0	0	0	0
0	0	0	1	1
0	0	1	0	2
0	0	1	1	3
0	1	0	0	4
0	1	0	1	5
0	1	1	0	6
0	1	1	1	7
1	X	X	X	None

X = Don't Care

CD4052

The CD4052 is an analog switch configured as a double-pole, 4-throw (DP4T) multiplexer, allowing for the selection of one of four differential signal pairs. It has two binary control inputs for channel selection.

Truth table for the CD4052

INHIBIT	B	A	ON CHANNEL(S)
0	0	0	X0, Y0
0	0	1	X1, Y1
0	1	0	X2, Y2
0	1	1	X3, Y3
1	X	X	None

X = Don't Care

CD4053

The CD4053 is a triple single-pole, double-throw (SPDT) analog switch, with each of its three channels individually controlled by an independent binary input.

Truth table for the CD4053

INHIBIT	C	B	A	ON CHANNEL(S)
0	X	X	0	ax
0	X	X	1	ay
0	X	0	X	bx
0	X	1	X	by
0	0	X	X	cx
0	1	X	X	cy
1	X	X	X	None

X = Don't Care

CD405x Data Sheet

CD4066

Quad Bilateral Single Pole Single Throw Switch

The CD4066 is an integrated circuit containing four identical, independently controlled single-pole, single-throw (SPST) analog switches, suitable for both analog and digital signals.

• Inputs and outputs are interchangeable, similar to conventional mechanical switches.
• Each switch is controlled by a dedicated binary control input.
• On-state resistance (R_ON) ranges from a few hundred ohms to over one thousand ohms, depending on V_DD.
• The absolute maximum input current per pin is 10mA.

Control Logic:

• Logic 1 (High) → Switch ON
• Logic 0 (Low) → Switch OFF

Applications:

• Signal Gating
• Signal Routing
• Transmission Gate Inverter

CD4066 Data Sheet

CD4060

14 stage ripple-carry binary counter/divider and oscillator. Q1, Q2, Q3 and Q11 are not connected to the outside of the package. A high level on input pin 12 resets the counter and disables the oscillator.

Applications:

• Frequency Divider
• Square Wave Generator

CD4060 Data Sheet

CD4013

The CD4013 IC flip-flop is called a D flip-flop type to characterize its behavior, while D stands for "data" or "delay". It contains two identical D flip-flop arrangements. The device stores a digital state 0 or 1, which is accessible at the output Q. The second output /Q presents the inverse of Q. The control input Clock transfers the input state D to the output Q respectively /Q. The CD4013 is positive-edge-triggered, which means that the positive-going transition of a clock impulse triggers the device to hold the state that is present at the input and provides it at the output until the next positive-going clock signal. The additional control inputs Set and Reset have priority over the clock. With a high level on the Set input, the output follows its state and goes low with a high level on the Reset input, ignoring D and Clock.

Applications:

• Frequency Divider
• Counter
• Toggle Switch

D flip-flop truth table

C	D	R	S	Q	/Q
/	0	0	0	0	1
/	1	0	0	1	0
⧹	X	0	0	no change	no change
X	X	1	0	0	1
X	X	0	1	1	0
X	X	1	1	1	1

X = Don't Care
/ = Rising Edge
⧹ = Falling Edge

CD4013 Data Sheet

CD4018 (under construction)

Divide-By-'N' Counter

When the outputs are fed back to the input Data, divide by 10, 8, 6, 4, 2, is calculated. For odd numbers 9, 7, 5, 3, simply use CD4011 or CD4093 to NAND two corresponding output stages and feed the inverted result back into Data. By combining multiple devices, higher divide-by functions can be calculated. Preset enable will transfer Data on the input Jam to its corresponding /Q (inverted). A logical high on the reset input causes all /Q Outputs to high.

Divide by 9: /Q4 & /Q5 via 1/2 CD4011 connected to input Data
Divide by 7: /Q3 & /Q4 via 1/2 CD4011 connected to input Data
Divide by 5: /Q2 & /Q3 via 1/2 CD4011 connected to input Data
Divide by 3: /Q1 & /Q2 via 1/2 CD4011 connected to input Data

Divide by 10: /Q5 connected to input Data
Divide by 8: /Q4 connected to input Data
Divide by 6: /Q3 connected to input Data
Divide by 4: /Q2 connected to input Data
Divide by 2: /Q1 connected to input Data

Applications:

• Divide by 10, 8, 6, 4, 2
• Divide by 9, 7, 5, 3
• Rhythm/Chord Generator

FUNCTIONAL TRUTH TABLE FOR CD4018

Clock	Reset	Preset Enable	Jam Input	/Qn
⧹	0	0	X	/Qn
/	0	0	X	/Dn
X	0	1	0	1
X	0	1	1	0
X	1	X	X	1

/Dn = Data input for that stage
X = Don't Care
/ = Rising Edge
⧹ = Falling Edge

CD4018 Data Sheet

555 Timer

Note: The bipolar version (NE555) and the CMOS version (TLC555, LMC555) have the same pinout and are exchangeable. The CMOS version consumes significantly less power. Its name derives from the three 5kΩ resistors that form a voltage divider network. This IC generates output pulses for precision timing or works as an oscillator with adjustable duty cycle. The timing function can be configured with just a few external components.

Applications:

• Frequency Divider
• Timer
• Pulse Delay
• Square Wave Generator
• Pulse Width Modulator

Pin	Function
1	Ground.
2	Start of timing input. TRIG < ½ CONT sets output high and discharge open.
3	High current timer output signal.
4	Active low reset input forces output and discharge low.
5	Controls comparator thresholds, Outputs 2/3 VCC, allows bypass capacitor connection.
6	End of timing input. THRES > CONT sets output low and discharge low.
7	Open collector output to discharge timing capacitor.
8	Input supply voltage, 4.5 V to 16 V.

In the astable configuration or multivibrator mode, the circuit generates a string of pulses by retriggering itself. Different values for $R_A$ and $R_B$ allow for changing the ratio of the high time and the low time. A low at reset pin 4 stops the oscillation. The time to complete one cycle (high and low) can be calculated with $T= ln(2) \cdot (R_A + 2R_B)C$ and the frequency with $f=\frac{1}{T}$.

For mono stable operation, a negative going pulse at the trigger input causes the output to go high for a defined amount of time (one shot). A second pulse within that time period has no effect on the output pulse and will be ignored. This circuit can be used for debouncing switches. The time the output stays high is set through the RC circuit and can be calculated with $T_H = ln(3) \cdot R_1C_1 \approx 1.1 \cdot R_1 C_1$.

The stepped-tone generator is built using two 555 timer chips. By varying the resistor-capacitor (RC) values, this circuit can produce a wide range of interesting sounds.

Designator	Description	Value
VR1, VR2	Potentiometer	500k
U1, U2	555 Timer
R1	Resistor	1k
C1	Capacitor	0,01uF
C2	Capacitor	0,1uF

LMC555 Data Sheet
TLC555 Data Sheet

LM386 - Power Operational Amplifier (under construction)

Although not part of the CMOS logic family this ubiquitous power op amp is a very versatile component when it comes to amplification or driving small speakers.

LM386 Data Sheet

Pin	Function
1	Gain setting
2	Inverting input
3	Noninverting input
4	Ground reference
5	Output
6	Power supply voltage
7	Bypass decoupling path
8	Gain setting pin

	min Voltage	max Voltage
Supply Voltage	4V	12V
Analog input voltage	-0.4V	0.4V

Basic Principles and Applications

Electronic-hydraulic analogy

The electronic-hydraulic analogy compares the flow of electrical current to water moving through pipes. In this model, voltage corresponds to water pressure, while current is analogous to the rate of water flow. Resistance is similar to the narrowing of a pipe, limiting the flow. Capacitors can be thought of as storage tanks or buckets that temporarily hold and release water.

Mixing

There are various ways of mixing signals together. Using CMOS chips like the XOR CD4070 works for digital signals. If more than two signals should be mixed or merged, several logic gates can be chained together. Even though the resulting signal is not the sum of the source signals but some modulated result, the output signal is still compatible with digital electronics. This is not the case with active and passive mixing, which alters the amplitude of the output. Active mixing involves components, such as operational amplifiers, that need a power supply. Passive mixing works without an additional power supply, but introduces a voltage drop.

Passive Mixing

Passive mixing is a very simple method that can be accomplished by using resistors for each source. The mixing resistors work as a voltage divider network and lower the amplitude of each signal. Therefore, the passive mixer doesn't give the sum of all input signals but the average. Small resistance values will drain more current and create distortion. Good values are between 10kΩ - 50kΩ. The advantage of this method is its low part count. To avoid attenuation and interaction between the signals and to obtain individual gain control, active mixing using an operational amplifier is preferred.

Active Mixing

For most audio applications it is desired to control the portion of each input signal in the sum of the output mix. For this, another class of active electronic components can be used, the operational amplifier (op amp). The basic wiring is shown below.

By adding voltage dividers or potentiometers, it allows for gain control over every individual input. Besides its function as a mixer, it can also be used to achieve the desired output gain by modifying the feedback resistor R_F in relation to the input resistors R_IN of each input. The minus sign in the formula indicates that the output voltage is inverted. To undo inversion, a second stage following the shown circuit can be used.

$V_{OUT} = - [ \frac{R_F} {R_{IN1}} V_{IN1} + \frac{R_F} {R_{IN2}} V_{IN2} + \frac{R_F} {R_{IN3}} V_{IN3} + etc.]$
$- V_{OUT} = \frac{R_F} {R_{IN}} [V_{IN1} + V_{IN2} + V_{IN3} + etc.]$ if all $R_{IN}$ are the same.

It should be underlined that the example shown is a single supply based circuit, which is uncommon for audio mixing where usually symmetrical dual supply voltages are used. It is important therefore to create a reference voltage of 1/2 V_CC at the non-inverting input. When working with logic circuits, the signals are almost at the supply levels. Even with rail-to-rail op amps caution is required to keep the summed signals below the working range of the op amp.

Passive Filters

Tone control, modifying the frequency spectrum of a signal or creative equalization are very important processes when working with audio. A filter is frequency-selective and passes only a desired range of frequencies, which is called the pass band. Outside of this pass band, frequencies are attenuated or ideally completely reduced. The boundary between pass and stop band is called cutoff frequency. The simplest way to shape an electronic signal is the use of a combination of resistor and capacitor, an RC element. This forms a first order filter. The circuit can be considered as a frequency dependent potential divider. A band-pass filter can be built with two RC elements, as a combination of a high-pass and a low-pass configuration. Since no amplifying components are involved, the amplitude of the output is lower than the input amplitude. When a filter is designed with two passive components, the transition from pass to stop band is rather smooth. For instance, a first order low-pass filter will have a 6dB/octave roll-off with increasing frequency. Unfortunately, the properties of passive filters are not sufficient to achieve a higher steepness or musical effects like resonance, which requires active filter designs. However, the simplicity and the low part count make this method very attractive for subtle tone control.

Potentiometers

A potentiometer is a passive, mechanical component enclosed in a housing. It consists of a resistive track and a movable contact called the wiper. The wiper’s position along the resistive track can be adjusted using an actuator.

The three terminals of a potentiometer provide access to:

• The two ends of the resistive element (fixed resistance between them)
• The wiper, which moves along the resistive track to divide the total resistance into two separate resistance values

Potentiometer Structure

a) Housing, b) Terminals, c) Actuator, d) Resistive track, e) Wiper

Potentiometer as a Variable Resistor:
If only one end terminal and the wiper are used, the potentiometer functions as a variable resistor, where the resistance varies based on the wiper’s position.

Potentiometer as a Voltage Divider:
By connecting a voltage source (e.g., supply voltage or signal) to one of the outer terminals and ground (GND) to the other outer terminal, the potentiometer acts as a variable voltage divider. The output voltage can be tapped from the middle (wiper) terminal and adjusted by turning the actuator.

For example, as the wiper moves from one end to the other, the output voltage scales continuously from minimum to maximum—making this configuration ideal for applications such as volume control.

Simplified schematic illustrating how to use a potentiometer as both a variable resistor (left) and a voltage divider (right).

LDRs (light-dependent resistors)

A photoresistor (also known as a light-dependent resistor, LDR) is a two-terminal electronic component whose resistance varies based on the amount of light hitting it (photoconductivity). The brighter the light, the lower its resistance, and vice versa. This makes it an effective light sensor that can be used to control sound. For example, if you place a photoresistor in the feedback loop of a CMOS oscillator, moving your hand over it to cast a shadow changes its resistance, which in turn alters the oscillator’s frequency (pitch). In this scenario, lower light levels produce a deeper pitch, while brighter light raises the pitch.

Two circuits using an LDR: a voltage divider adjusting output voltage based on light levels (left) and a Schmitt-trigger oscillator where light controls the pitch (right).

Pull-up and Pull-down Resistors

When connecting external circuits or devices to a logic gate, it's important to ensure that the inputs remain in a defined state. Floating inputs (inputs that are left unconnected) can behave unpredictably due to their high impedance, making them highly susceptible to electromagnetic noise. For example, when a normally open push button is in its default position (not pressed), it effectively disconnects the input. In this state, the logic input may pick up random interference, causing the circuit to behave erratically by generating unintended high or low signals. This phenomenon is known as "floating", leading to unreliable circuit operation.

To prevent unpredictable behavior, a pull-up or pull-down resistor should be connected to either V_CC (high voltage) or GND (ground). This ensures that the input remains in a defined state even when no active signal is applied, such as when a switch is open. When the switch is closed, the input can still receive a valid signal.

• A connection to V_CC is called a pull-up resistor, keeping the input high (logic 1) by default.
• A connection to GND is called a pull-down resistor, keeping the input low (logic 0) by default.
• For CMOS logic, typical resistor values range from several kilo-ohms (e.g., 10kΩ – 100kΩ).

Even unused logic gates can cause issues, as they may pick up interference, leading to false triggering or increased power consumption. To ensure stable operation, all unused inputs should be tied to either GND or V_CC instead of being left floating.

Exploratory Sound Circuits

This section features a selection of DIY sound circuits that explore the creative possibilities of CMOS chips. They serve as a starting point for hands-on experimentation and modification. These circuits can be combined with the basic circuitry examples above or extended using them, allowing for even more complex and dynamic sound generation

Linear Feedback Shift Register

A linear feedback shift register (LFSR) can be used for generating deterministic pseudorandomness. In terms of electronic sound production it can be used to build a noise source. An LFSR consists of n numbers of flip-flops which are connected in series to form a shift register as described for the CD4015. This shift register is controlled by a clock that triggers the shift process. Two junctions at a specific position within that chain of flip-flops are directed into an XOR logic gate. The resulting value is fed back into the first register. The number of stages can be extended by connecting multiple devices. The produced values are determined by the shift register's current states and total length. Since the states are finite it will repeat after a certain number of steps. The goal is to choose those taps that form the longest possible sequence of zeros and ones before they repeat. Other implementations of an LFSR exist and work similarly. To activate an LFSR each stage needs to be loaded with an initial value. This is called the seed. By using an XOR function for the feedback, having the value 0 in all flip-flops is forbidden. By using an XNOR function it is forbidden to set all flip-flops to 1. A maximum-length sequence is therefore 2ⁿ - 1. No matter if XOR or XNOR functions are used, the sequences will have the same length. The duration of one cycle is determined by the clock frequency. When looked at a shift register from the viewpoint of a musician, the long LFSR arrangements will create white and pink noise when controlled with a high frequency (several ten thousands of hertz). Shorter cycles produce grainy tones, stuttering textures or short noise loops.

The Xilinx application note XAPP210 (V1.3) and the Maxim Integrated (now Analog Devices) application note APP4400 (Jun 30, 2010) show tables for maximum length sequences, which are presented here for up to 32 bits:

n	taps from	length		n	taps from	length		n	taps from	length
3	3,2	7		13	13,4,3,1	8,191		23	23,18	8,388,607
4	4,3	15		14	14,5,3,1	16,383		24	24,23,22,17	16,777,215
5	5,3	31		15	15,14	32,767		25	25,22	33,554,431
6	6,5	63		16	16,15,13,4	65,535		26	26,6,2,1	67,108,863
7	7,6	127		17	17,14	131,071		27	27,5,2,1	134,217,727
8	8,6,5,4	255		18	18,11	262,143		28	28,25	268,435,455
9	9,5	511		19	19,6,2,1	524,287		29	29,27	536,870,911
10	10,7	1,023		20	20,17	1,048,575		30	30,6,4,1	1,073,741,823
11	11,9	2,047		21	21,19	2,097,151		31	31,28	2,147,483,647
12	12,6,4,1	4,095		22	22,21	4,194,303		32	32,22,2,1	4,294,967,295

Depending on the desired operation, other applicable devices may be CD4094, CD4014, CD4021 which are all 8-stage shift registers.

This video displays an excerpt of a maximum sequence length of 2147483647 bits, generated with a 31 bit long shift register and the 28th tap. The clock rate is 5 Hz.

Pseudo-random_sequence_V2.mp4

Step Sequencer (under construction)

This circuit for a step sequencer is shown in N. Collins book 'Handmade Electronic Music'. It makes use of the built-in voltage controlled oscillator (VCO) of the CD4046 Phase-Locked Loop. The voltage levels of the output pulses of the CD4022 counter can be scaled down by the potentiometer voltage dividers and are mixed together via the diodes D1-D8 (1N4148). The CD4046’s voltage controlled oscillator is then generating a frequency according to the input voltage level. Therefore, each step Q0-Q7 of the CD4022 can be used to produce a single tone.

Input voltage (blue graph) and VCO frequency (yellow graph) of the CD4046.

A logical high on the 'Clock Inhibit' of the CD4022 stops the counter advancement and hence the sequence. A manual push button switch with a pull down resistor to GND or a control logic circuit can be used to pause the sequence for rhythmic effects. A logical high on the 'Reset' input restarts the counter. Connecting one of the outputs of the counter to the 'Reset' pin shortens the length of the sequence by one in regard to the number of the used output. (Step length = Qx-1, if Qx is connected to 'Reset'). More complex patterns can be created when the reset and the inhibit functionality is dynamically controlled by logic circuits.

A clock source is needed for triggering the CD4022. When the clock is set to an audio frequency, the step sequencer works as a wave shaper. Pin 5 (Inhibit) of the CD4046 must be set to a logical low for operation. The frequency range of the CD4046 VCO can be set via the two resistors connected between pin 12 and ground and pin 11 and ground. According to the schematic below, a rough approximation can be calculated with the following formula:

$f_{min} = \frac{1} {{R_5}(C_1 + 32 pF)}$
$f_{max} = \frac{1} {({R_4}+VR)(C_1 + 32 pF)} + f_{min}$

The output of the VCO can be gated with the clock source through a CMOS switch, e.g. CD4066.

Bill of Material:

Designator	Description	Value
D1, D2, ... (for each step)	Diode	1N4148
VR	Potentiometer $f_{max}$	100K
VR1, VR2, ... (for each step)	Potentiometer	100K
R1*, R2*	Resistor	1K - 10K
R3	Resistor	100K
R4	Resistor $f_{max}$	10K
R5	Resistor $f_{min}$
C1	Capacitor	100nF
SW1, SW2 (optional)	push button or toggle switch	on - off
CD4022	Counter
CD4046	PLL
Clock	Clock Generator (eg. CD40106)

Melody Generator

Schematic of Slacker's Melody Generator—a CMOS sound generator using a CD4017 counter and a CD4051 multiplexer to produce evolving, semi-random melodic sequences.

Voltage Starve

“Voltage starve” or “voltage sag” can be used as an unconventional modulation technique in experimental music, describing the effect of a low supply voltage and limited current on a circuit’s behavior. In particular, battery-powered guitar pedals can exhibit unique dynamic distortion when the battery’s voltage and current delivery capacity deteriorates over time.

Changing the supply voltage has different effects depending on the circuit topology and component choices. Bypass capacitors help stabilize the power rail, but for instance, the hysteresis thresholds in Schmitt trigger elements vary with supply voltage. Consequently, lowering the supply voltage alters both the frequency and amplitude of Schmitt trigger oscillators.

When using an adjustable power supply or a custom-built circuit, you can explore how limited current and reduced voltage—especially near or below an IC’s minimum requirements—impact performance. A similar effect can be reproduced simply by placing a series resistor in the power rail. Experimenting with potentiometers ranging from 500 Ω to 10 kΩ can yield a variety of unusual modulation effects.

Materials

Instructions, parts, tools, shopping lists, components, assemblies, and other materials required to create electronic projects in this field.

Requirements

Helpful tools and useful materials:

• Small mixing desk.
• Active loudspeakers.
• Worktables.
• Pen and paper for drawing schematics.
• Screw drivers.
• ESD electronic diagonal cutter.
• Precision cutter.
• Stranded wires.
• Crocodile clips.
• Laboratory power supply & connectors (preferable 4mm banana laboratory connectors).
• Jumper cables and jumper wires.
• Digital multimeter (DVM).
• Digital storage oscilloscope (DSO).
• Temperature-controlled soldering station.
• Breadboards.
• 9V Batteries.
• Battery clips.
• Good light conditions.

Bill of Materials (BoM)

This BOM helps to source necessary components for electronic art projects and self-built instruments.

Artists

Circuitry-Based Sound are:

Marc Bendt
Bent van den Berg
Fangchao Bi
Zhen Bian
Yinxuan Chen
Hangyan Chen
Siting Chen
Haram Choi
Mark Damian
Thabisa Dinga
Kurt Diedericks
Tobias Ehrhardt
Jung Eun Lee
Damiana Facen
Bi Fangchao
Qianqian Feng
Zufilkar Filandra
Hongyu Guo
Jeongmin Han
Juhee Han
Anna-Lina Helsen
Keita Hori
Jihye Jang
Hoin Ji
Minsu Kim
Florian Knöbl
László Kőrösi
Sangyi Lee
Xingchen Liu
Su Lu
Daniel Lythgoe
Ziyang Ma
Mqhorhana Magqaza
Simphiwe Matole
Jason Mendiola
Victoria Mikhaylova
Lakheni Ntsodo
Jiun-You Ou
Isabella Panigada
Azile Plaatjies
Ukwanda Plaatjies
Pavel Polenz
Max Pospiech
Ruoyi Qiu
Bob Reinert
Vivian Reuter
Arno Schlipf
Dario Schmid
Florian Schwarz
Yifan Su
Anna Szilágyi
Eveline Vervliet
Christina Vinke
Julian Vollmert
Aaron Wagner
Niklas Wallbaum
Dakang Wang
Yudong Wang
Lutz Ben Wesch
Eunchae Won
Le Yang
Sayuki Yoneda 
Jiahui Yong
Huiyeon Yun
Rui Zhang
Yunfei Zhang
Xinyi Zhao
Yange Zheng
Pei Zhou

Lorenz Schwarz - lecturer

Acknowledgment

Thanks to Dr. Paul Modler, Dizu Plaatjies, Dr. John Richards, Theo Herbst, Dr. Paul Rommelaere, and Holger Förterer.

Literature

Anderton, Craig. Electronic Projects for Musicians. Amsco, 1980.

Barlow, Klarenz. On Musiquantics. Bereich Musikinformatik, Musikwissenschaftliches Institut, Johannes Gutenberg-Universität Mainz, 2012.

Brindley, Keith. Starting Electronics. Newnes, 2011.

Collins, Nicolas. Handmade Electronic Music: The Art of Hardware Hacking. Taylor & Francis, 2009.

Horowitz, Paul and Winfield Hill. The art of electronics. Cambridge University Press, 2021.

Lancaster, Don. Das CMOS-Kochbuch. IWT-Verlag, 1980.

Maxfield, Clive. Bebop to the Boolean Boogie: An Unconventional Guide to Electronics. Newnes, 2003.

Roads, Curtis. Computer Music Tutorial. The MIT Press, 1996.

Self, Douglas. Small Signal Audio Design. Focal Press, 2020.

Tate, Timothy, et al. „Hand Turned Synthesis: A One Chip Exploration of CMOS Electronics“. Proceedings of the International Conference on New Interfaces for Musical Expression, Zenodo, 2024, S. 612--621, doi:10.5281/zenodo.13904971.

Links

Below are links to various online resources related to audio electronics and Synth DIY, as well as inspiring websites from artists and researchers:

Nicolas Collins - Sound artist, composer and performer of electronic music.
https://www.nicolascollins.com

John Richards - British musician and artist. Self-made instruments, installations and sound projects with electronics.
https://www.dirtyelectronics.org/about.html

Handmade Electronic Music - Hands-on guide to DIY electronic instruments by Nicolas Collins.
www.HandmadeElectronicMusic.com

Klarenz Barlow - Pioneer and celebrated composer in the field of computer music and influential teacher.
http://clarlow.org/texts

Eberhard Sengpiel - Sound engineer, musician, lecturer. Sound studio and audio calculations, audio and acoustics conversions.
http://www.sengpielaudio.com

audiodiwhy - DIY music technology, programming.
https://audiodiwhy.blogspot.com

Electric Druid - About audio electronics and analogue synthesizers.
https://electricdruid.net

Synthesizer DIY website of René Schmitz
https://www.schmitzbits.de

Elliott Sound Products - Professional results for the Do-It-Yourself enthusiast.
https://sound-au.com

The Institute of Sonology - Informational website from the Royal Conservatoire in Den Haag about electronics for art and education.
https://electronics.koncon.nl

Adrian Freed - Former Research Director of UC Berkeley's Center for New Music and Audio Technologies (CNMAT).
Ideas, projects, examples regarding creative and artistic use of electronics in sound and music.
http://www.adrianfreed.com

diyaudio forum - DIY audio community forum for learning and sharing knowledge about music technology and audio electronics.
https://www.diyaudio.com

electro-music forum - Dedicated to experimental electro-acoustic and electronic music.
https://electro-music.com

modwiggler forum - Source of information about modular synthesizers and DIY analog circuits.
https://www.modwiggler.com

License

The content of this documentation is licensed under the Creative Commons Attribution 3.0 Unported license, software is licensed under the MIT License - see the LICENSE.md file for details. Copyright remains with the author(s)