After applying the 24V power supply to the circuit, the signal splits into two directions. The first one goes directly to the Solenoids that are driven with PWM signals through the microcontroller:
PWM stands for Pulse Width Modulation. It is a technique used to control the amount of power delivered to a load by controlling the duration of a series of pulses. The duty cycle of a PWM signal is the proportion of time that the signal is in the “on” state (high) compared to the total period of the signal. It is typically expressed as a percentage. For example, if a PWM signal has a duty cycle of 50%, it means that the signal is in the “on” state 50% of the time and in the “off” state 50% of the time. The relation between the duty cycle and the power delivered to the load is that a higher duty cycle corresponds to more power delivered to the load. To avoid burning the magnet,
The second goes across the DC/DC Stepdown converter that transforms the power into 5V since the ESP32 microcontroller produces only 3.3V (not enough to drive efficiently the motors).
Besides this project, I had already some experiences this semester to explore the possibilities in the field of music machines. For the final presentation in “ESC medien kunst labor” I presented a plastic “Hackbrett” played by one DC Motor. The generated sound was then recorded and processed in real-time via PureData.
The interaction with the instrument occurred using a 3D-printed cylinder mounted on the motor. The different slices on the sides were positioned at equal distances to insert guitar picks. The goal was to emulate an analog score capable to play different patterns according to the distances between the picks.
Even though this process seemed to be satisfying, due to the distance to the strings and the movement of the motor, it was difficult to manage a continuous pattern or intensity. For this reason, after discussing the idea with professor Ritsch, we obtain for the solenoids to play the instrument.
Next, I designed a prototype with only one string and a hammer with additionally a lever to be able to change the pitch of the string and obtain further nuances in the timbre. The idea is to build a simplified version of the final machine to analyze the possibilities, limitations, and different technical challenges of this instrument. Although the construction is very rudimentary, through this process, I would learn useful information to better set the technical components and then decide how to play it from the artistic point of view.
The system works mechanically through two core elements: the hammer that reproduces the percussive sounds (solenoid) and the lever (servo motor) that contributes to shifting the pitch. With the first one I reproduce different rhythmical patterns that can be modified in real-time by means of pre-programmed sequences and with the lever, like for an electric guitar, I produce timbral variations in the frequency domain.
The image below represents the first sketch of the prototype:
Regarding the electronic part of the development process, I took inspiration from a project made by Professor Ritsch during my second semester at IEM, the “Coeus”:
“previous “autodrummer” and later percussion robot aka “Doppelschlagwerke”, now robot musician is targeted building robotic instrument player with microcontrollers in the IoT generation, which are designed to play all kind of drums, gongs, pipes, strings … or other similar new created instruments or sounding objects very accurate and dynamically as quickly as possible or slow with optional dampers – making up a automata as instrument player, a robotic musician controllable over a network via OSC (Open Sound Control Syntax).”[1]
Analyzing his concept, I reorganized the electronic parts I needed to design a robot that would meet my technical requirements. Here the list of electronic components that I used:
[2] Servomotor – CDN-Reichelt.de (no date). Available at: https://cdn-reichelt.de/documents/datenblatt/A300/COM-MOTOR02-DATENBLATT.pdf (Accessed: January 26, 2023).
[3] DC-DC Stepdown Modul LM2596S (no date) 3DJake Österreich. Available at: https://www.3djake.at/bigtreetech/dc-dc-stepdown-modul?gclid=CjwKCAiA5sieBhBnEiwAR9oh2v_YBqQJkIaTMVZ3Pr1sqGGeMtlf2k7Fa4m72bm-v9hGE5iRAfGhzxoCTWoQAvD_BwE (Accessed: January 26, 2023).
The “Hackbrett”, also known as a hammered dulcimer, is a stringed musical instrument that is played by striking the strings with small hammers. The strings are stretched over a trapezoidal-shaped soundboard and are divided into two sections: the treble, and the bass. The treble section typically has more strings and is played with the right hand, while the bass section has fewer strings and is played with the left hand.
It is a diatonic instrument, meaning that the notes it produces are based on a specific diatonic scale and not chromatic like piano for instance.
The hammers or beaters have padded heads, which allow the player to produce a variety of different tones and dynamics depending on the amount of force used to strike the strings.
The “Hackbrett” is a versatile instrument that can be used to play a wide range of musical styles, including folk, classical, and popular music. It has a unique and distinctive sound that is often used to add a touch of character and interest to a musical arrangement.
The way it works is by using the hammers to strike the strings, the hammers will make the strings vibrate and produce sound waves. These sound waves will then travel through the soundboard and out of the instrument, which is how the sound is projected. The hammers can be used to strike the strings at different points along their length, which produces different pitches.
The “Hackbrett” has a long and rich history in Austria, where it has been played for centuries. The earliest known reference to the instrument in Austria dates back to the 15th century. The instrument was brought to Austria by German and Italian traders, and it quickly became popular among the peasant population.
In the 16th and 17th centuries, was primarily used as an accompaniment instrument for folk music and dances. It was also commonly used in religious music and in the courts of noblemen and aristocrats. The instrument’s unique sound and versatility made it a popular choice for both solo and ensemble performances.
During the 18th and 19th centuries, the “Hackbrett” experienced a decline in popularity, as it was replaced by the piano in many musical settings. However, the instrument continued to be played in rural areas and among folk musicians, who kept the tradition alive.
The “Hackbrett” is essentially a resonance box with strings strung above it that are played with wooden sticks, “Ruten” or “Schlägerli” in German. One note can be played onE up to five strings. Choruses are the name given to such chords.
A middle bridge that divides the strings in a specific ratio is frequently found on these choirs. Pure fifth results, for instance, from dividing a string in the ratio 2:3. This could mean, for instance, that a C is located on the bridge’s right side and a G is located on its left, or the opposite. For the best results, you should hit the strings three to four centimeters from the bridges.
After concluding my studies at the Institute for electronic music (IEM), where I wrote my bachelor thesis about a possible application of a glove as a musical interface, I decided to continue my research in the field of music machines and their capabilities.
Since the Sound Design department of the “FH Joanneum” has been invited to participate to the event “Salzkammergut 2024” to produce a physical music machine employing the traditional instruments from that region, I focused my work on the analysis and research of the “Hackbrett” as a topic of this semester. I aim to discover the peculiarities of this percussive-melodic instrument to produce a prototype able to reproduce human behavior while playing it.
Using small electronic components such as DC motors and solenoids, this project attempts to reproduce the technique and aesthetics of this instrument. The final product will be a music machine equipped with different servo motors and two solenoids for each string.
Under the supervision of Professor Winfried Ritsch, I conducted some research regarding its tradition and its role in the Austrian culture, to propose a simplified system that should represent the core of the instrument that I’m going to build next semester: the “One Wire Hackbrett”.
During this semester, I was able to learn countless notions that led me to the realization of the first prototype of this instrument.
Despite the difficulties, I was able to narrow down the field of variables and question marks that stand between me and the realization of the final product. Through research and experimentation, I acquired the skills to be able to plan the following steps that separate me from the final goal: the realization of a fully automated Hackbrett.
About the physical construction of the instrument. The next step is to build a support capable of holding the hammers for each string of the instrument. As already demonstrated with the prototype, the aim is to obtain a modular structure that can be customized according to technical and artistic requirements.
From the software point of view, the next step is to create a GUI in Pure Data to control the instrument via OSC (Open Sound Control). As a starting point, I will use the library written by Professor Ritsch, LEMiot[1]:
“Making Computermusic Devices using ESP32x with various sensors and actors is the overall goal for the LEMiot project. Using IoT (Internet of Things) technology to interact in Music Performances and Theatre projects or as sound installations. This library is a firmware framework for controlling LEMiot boards using the library ‘OSC_networking’ as device and WiFi management, parameter storage and additionally a simple user interface with LEDs and buttons. Each board as an incarnation extends these functionalities by integrating additional sensors or actuators. The device can be controlled wirelessly using a special ‘OSC’ protocol. A Configuration Tool with Puredata as also a corresponding Puredata library”
This step will enable me to learn the different techniques for interacting with the instrument and the parameters to be mapped. Moreover, the skills to program my own Networking environment.
Another important step to be taken, is the realization of a functional algorithm for the pitch detection. As discussed in previous chapters, my initial approach involves utilizing zero crossing analysis on each individual set of strings. To accomplish this, I will divide my tasks into two sub-levels: software and hardware:
– regarding the software aspect, I will employ the “~zexy”[2] extension for Pure Data, developed by Professor Johannes Zmölnig. This extension provides valuable examples and resources for pitch detection using zero crossing techniques. By studying these principles, I will gain a solid foundation and understanding. Eventually, I aspire to write my own pitch detection algorithm directly on the microcontroller, allowing for a more streamlined and integrated solution.
– regarding the hardware part, I will use the Calliope-board[3] for the further developments. This board offers several advantageous features, including six microphone inputs and an integrated Mosfet system designed for solenoids. These components encompass all the necessary elements to realize the final product effectively.
The final element that remains is the development and integration of a servo motor system for tuning the instrument. However, I have not yet discovered a suitable approach for this specific purpose. The Hackbrett’s strings are closely spaced, which presents a challenge in independently controlling them. Therefore, our initial step will involve designing a system similar to the one depicted in the provided image /Fig. 1).
[1] Ritsch, Winfried UC / LEMiot library · gitlab, GitLab. Available at: https://git.iem.at/uC/LEMiotLib (Accessed: 16 June 2023).
[2] Pure Data Libraries / Zexy · GITLAB (no date) GitLab. Available at: https://git.iem.at/pd/zexy (Accessed: 16 June 2023).
[3] Ritsch, Winfried IEM development area, Sign in · GitLab. Available at: https://git.iem.at/ritsch/calliope (Accessed: 16 June 2023).
In the initial phase, I embarked on a series of experiments using PD (Pure Data) to analyze the input signal derived from my prototype. Here the aim was to understand how to get the parameters for the servos to tune the strings.
At first, I employed an FFT (Fast Fourier Transform) algorithm to determine the algorithm’s ability to track the pitch of the incoming signal and see how reactive and precise the analysis response while changing the tension of the strings.
To achieve that, once obtained the fundamental and the first three partials of the incoming signal, I divided the process into two steps:
convert the difference of the estimated pitch and the incoming signal (changing the tension) into semitones:
attribute the estimated difference in semitones as pitch parameter of a “pitchshifter”.
The limitation:
FFT analysis of complex signals and the latency introduced while processing the data:
the interference between the harmonics produced by different strings can create complex frequency interactions that are not easily captured by a simple conversion method. To improve the reliability of the analysis, it would be necessary to employ more sophisticated techniques that take into account the complex harmonic relationships occurring during simultaneous string play. This could involve employing advanced signal processing algorithms or considering the specific characteristics of each string, such as its tuning, tension, and resonance properties.
The second step consisted into the application of zero crossing analysis to find the pitch of the strings. Even though I was not able to implement this process during this semester, I came out with rather interesting solutions to implement it.
First a brief introduction to the subject… In the audio domain, zero crossing[1] is an important concept that is frequently used in pitch recognition and estimation. Pitch recognition refers to the process of identifying the fundamental frequency or musical pitch of a sound.
Zero crossing analysis is employed as a technique for pitch recognition due to its effectiveness and simplicity. The fundamental frequency of a sound corresponds to the rate at which the waveform crosses the zero level. By counting the number of zero crossings within a specific time frame, it is possible to estimate the pitch of the sound.
As we traverse through the audio samples, we examine each point. If the amplitude of the current sample (N) is equal to the silent threshold and the amplitude of the following sample (N + 1) is either higher or lower than the silent threshold, then the sample point at (N) is identified as a zero-crossing point. Once we determine the number of zero crossing points, we can utilize the sampling rate of the signal and the total number of samples to calculate the duration in seconds over which these zero crossing points were counted.
The formula for this calculation is:
Number of seconds = Total number of samples / Sampling rate
Considering that each oscillation of a signal encompasses two crossings of the silent threshold, we can determine the number of oscillations by dividing the total number of zero crossing points by two.
The formula is:
Number of oscillations = Total number of zero crossing points / 2
To ascertain the frequency of the input audio signal, we employ the values obtained from steps 2 and 3. The formula for calculating the frequency in Hertz is:
Frequency of input audio signal = Number of oscillations / Number of seconds
The methodology of zero crossing analysis offers various approaches and combinations that can yield accurate results. However, upon analyzing different projects, it becomes evident that limitations arise when the input signal comprises multiple simultaneous sounds rather than a single waveform.
To overcome the challenge of analyzing complex instruments like the Hackbrett, I have reached a possible realization for the upcoming developing time. When dealing with instruments that produce overlapping sound sources, such as multiple strings being played simultaneously, it becomes essential to implement a specialized approach to improve the accuracy and reliability of the analysis.
One effective solution involves recording each string separately and isolating their individual signals. Moreover, since we already know the frequencies associated with each string, we can leverage this information to our advantage by applying a “third-octave filter”[2] at the input stage to attenuate any potential interferences arising from other strings.
After researching about the topics, I encountered one project made at the IEM by Winfried Ritsch about acoustic of music instruments, the “IAAI[3]”:
“The basic idea is to use the acoustics of the instrument as an instrument, for example as part of a feedback loop. In the acoustics of an instrument, we consider the entire signal path, from the excitation of the strings to the radiation, so pickups in combination with loudspeakers and magnetic actuators for vibrating strings are also part of the acoustic system of the instrument”
Even though the purpose of this research is focused on other aspects, it shows an implementation of technics that fit to my research about finding the best way to detect the pitch.
In the specific, the idea of using the “Varitone”[4] to build resonant filters.
The “Varitone” is an electronic circuit found in electric guitars that alters the sound by changing the frequency response. It uses capacitors and resistors connected to the guitar’s pickups to create a low-pass filter network. A rotary switch on the “Varitone” circuit selects different capacitor and resistor combinations, changing the cutoff frequency of the filter.
Rotating the “Varitone” switch modifies the circuit’s capacitors and resistors, which adjusts the cutoff frequency. This affects the amount of treble reduction, resulting in different tones. By passing the guitar signal through various capacitor and resistor combinations, the circuit modifies the frequency response, impacting the amount of high-frequency content reaching the amplifier and creating tonal variations. Since the principle of this system consists precisely in obtaining filters that can be set to different frequencies, I thought of combining this technique for a system of piezo microphones positioned on the instrument.
In the Fig. 8, a draft made by Professor Ritsch that represent the electronics of this system.
Once the strategy of how to apply the electronics to filter the input signal has been analyzed, I moved on asking myself how to record the signal coming from each string. Here two approaches that I have identified as possible solutions to record the strings separately:
handmade pickups made by ferrites;
elastic pickups (Fig. 11) that I used in the past to build guitars and positioning them underneath each choir of the Hackbrett. The advantage of using this piezo is that I could cut them into small pieces and make different microphones from one stick. As we can see in the Fig. 10, I divide the strings into channels to be sent to the pitch detector. Once the analysis is done, I compare the outcoming frequency with the given one of the string to adjust then the servo motor.
[1] Daoo, R. (2020) Algorithmic frequency/pitch detection series – part 1: Making a simple pitch tracker using zero…, Medium. Available at: https://medium.com/the-seekers-project/algorithmic-frequency-pitch-detection-series-part-1-making-a-simple-pitch-tracker-using-zero-9991327897a4 (Accessed: 09 June 2023).
[2] Third-octave filter banks. Available at: https://ccrma.stanford.edu/realsimple/aud_fb/Third_Octave_Filter_Banks.html (Accessed: 09 June 2023).
[3] Ritsch, Windried (no date) Imle, iemCloud. Available at: https://cloud.iem.at/index.php/s/oXcznxBe2TMmZbn?dir=undefined&path=%2FIAAI%2Fdoku&openfile=2966930 (Accessed: 16 June 2023).
[4] Selmer Varitone (no date) TCGAKKI. Available at: https://tcgakki.com/en/pages/selmer-varitone (Accessed: 16 June 2023).
The development of accurate and reliable string tuners has been a subject of great interest and innovation in the field of music technology.
As a result, numerous projects and technologies have emerged, each aiming to provide precise pitch detection and tuning capabilities for stringed instruments. In this analysis, we compare two prominent projects in the field of pitch detection string tuners to identify the most effective approach for advancing my own project:
By analyzing these two projects, I aimed to identify the strengths and weaknesses of each approach and determine the most effective way to proceed with our own pitch detection string tuner project. This analysis will consider factors such as accuracy, precision, responsiveness, hardware components, software algorithms, and potential areas for improvement. The goal is to leverage the insights gained from these existing projects to guide the development of our own innovative and highly precise pitch detection string tuner.
The Motorized Guitar Tuner (Fig. 6) is a hand-held device designed to automatically tune an electric guitar using a micro-controller and a servo motor. The device processes the guitar signal input precisely to provide high accuracy and implements an appropriate controlling algorithm for actuating the motor. The tuning results are quite good, but the accuracy is limited by the interaction of the different strings with each other and the guitar neck. The document discusses various methods for detecting zero crossings and generating PWM signals for controlling a servo motor. In the 2.2.4 chapter, the pure zero crossings method is discussed as a way to determine zero crossings without any previous calculations. However, this method was found to be unusable due to the presence of harmonic oscillations in the guitar string signal. On the other hand, the autocorrelation method was found to be more promising as it can point out periodic components very well, even in the presence of noise or distinctive harmonic oscillations. Therefore, the autocorrelation method was chosen as the preferred method for frequency detection.
The second project create a mechatronic string instrument called “Cyther V3” (Fig. 7) that can autonomously tune each string during a performance. The tuning system senses string tension, estimates pitch, adjusts the tension, and corrects for errors in estimation using optical pickups. The tuning system was tested and found to be accurate within +/- 8 cents, but not precise enough for error to go undetected by human perception.
The tuning system is designed to sense the pitch of each string in a way that allows the instrument to create various pitch changing techniques like portamento and vibrato at all times during a performance. The system uses tension sensors to sense the tension in each string and estimate the pitch of the string. The actuators of this tuning system should be able to adjust the pitch of any string by a semitone in 100ms or less.
The software has a form of closed loop control to keep every string at a desired pitch. It should adjust the pitch estimation function over time to compensate for small changes to the instrument that alter the strings’ pitches.
The system uses optical pickups to measure the frequency of each string. The frequency information is used to update the curve that relates the frequency of the string to the tension sensor’s potentiometer value to prevent the error in the tuning system from compounding.
[1] TU Graz. Available at: https://www2.spsc.tugraz.at/www-archive/downloads/MGT_documentation.pdf (Accessed: 09 June 2023).
[2] Dynamically tuning string instrument – web.wpi.edu. Available at: https://web.wpi.edu/Pubs/E-project/Available/E-project-012317-195256/unrestricted/Dynamic_Tuning_MQP.pdf (Accessed: 09 June 2023).
In my ongoing research on controlling solenoids, I have been exploring the use of PWM (Pulse Width Modulation) as a strategy to control these actuators. To enhance my understanding, I studied the work of Professor Winfried Ritsch, who has extensively researched this topic. Specifically, I found his “PWMEnvelope” [1] repository to be a valuable resource for experimenting with my instrument.
In this chapter of my research, I aim to summarize the key points that are essential for understanding and implementing Professor Ritsch’s code. By simplifying the concepts and principles, I hope to provide a clear overview of how the code functions and how it can be applied to my own project of controlling solenoids.
Envelopes are used to control PWM signals. In the attack phase, there is a fade to gradually reach the stroke level. After the stroke time, a sustain phase is applied to maintain the desired level, followed by a release phase to fade out the signal. By working with these parameters, we directly influence the timbral result. Like a piano key, by changing the level of pressure and duration of the attack we can achieve different sonic results. To ensure the safe operation of these devices, especially when using duty cycles lower than 100%, “PWM one-shot pulses” are utilized to prevent any potential issues.
Attack Stroke Hold Release for solenoids:
_ stroke level
/ |_____ hold level
_ / \_ off
A S H R times
To implement this functionality with the ESP platform, the LED-C Library[2] is used for generating the PWM signal, while the Timer library handles the one-shot timer feature.
The LED Control (LEDC) peripheral is a feature of ESP32 microcontrollers that is primarily used for controlling the intensity of LEDs. However, it can also be used to generate PWM signals for other purposes. The LEDC has 8 channels, each capable of generating independent waveforms. The LEDC channels usually have a 4-Channel high-speed mode and a 4-Channel low-speed mode, which provide different ranges of frequency for LED control.
The specific frequencies achievable in each mode may vary depending on the microcontroller or LED driver being used. These channels can be used to drive RGB LED devices, among other applications. The PWM controller of the LEDC allows for gradual increase or decrease of the duty cycle, enabling smooth fades without requiring processor intervention.
To set up a channel in the LEDC, three steps are involved:
Timer Configuration: Specify the PWM signal’s frequency and duty cycle resolution;
Channel Configuration: Associate the channel with the timer and GPIO pins to output the PWM signal;
Change PWM Signal: Modify the PWM signal to control the LED’s intensity.
The ESP32’s Timer Library[3] can be used to generate PWM signals by configuring it to repeatedly count up to a certain value and then reset. The ratio of the time it takes to count up to the reset value compared to the total period determines the duty cycle of the PWM signal. By adjusting the duty cycle, it can control the average power or intensity delivered to the device connected to the output pin.
When using multiple libraries or processes that rely on timers in the ESP32 microcontroller, it is advisable to allocate each process to a specific hardware timer or counter to avoid interference between the processes. By assigning dedicated timers to different processes, potential conflicts, such as conflicting interrupt handling or timing discrepancies, can be avoided. Moreover, assigning separate timers to different processes helps maintain the integrity of each process’s timing operations and provides precise timing control.
[1] Ritsch, W. IEM development area, Sign in · GitLab. Available at: https://git.iem.at/uC/pwmenvelope/-/tree/master/examples/playing (Accessed: 11 June 2023).
[2] Led control (LEDC) ESP. Available at: https://docs.espressif.com/projects/esp-idf/en/latest/esp32/api-reference/peripherals/ledc.html (Accessed: 11 June 2023).
[3] General purpose timer (no date) ESP. Available at: https://docs.espressif.com/projects/esp-idf/en/v4.3/esp32/api-reference/peripherals/timer.html (Accessed: 16 June 2023).
In this project, we explore the ongoing development of a project that began last semester, focusing on the creation of a musical instrument using microcontrollers and actuators. This semester, I have continued my research by building a prototype that demonstrates the basic functions to be implemented in the final product. Let’s take a journey through the design and realization phases, uncovering the steps that led me to choose the right materials and programming strategy for this project. Starting off, I conducted thorough research into musical instruments, their construction, and the mechanics behind their sound. With this insight, I moved into the design phase, blending creativity with practicality. I carefully considered the materials that would enhance the instrument’s expressiveness and capture its unique character. Through sketches and inspiration, I crafted a blueprint that aimed to create a captivating musical experience. However, design alone couldn’t bring the instrument to life; it required the combination of artistic and engineering skills. This led me to microcontrollers and actuators, which play a vital role in animating the instrument. The construction of the prototype marked a significant milestone. I brought my creative vision into tangible form. The prototype showcased the instrument’s essential features, demonstrating innovation and musical features. As the semester comes to an end, I am inspired by the melodies produced by the prototype, motivating me to refine every detail for the final product.
Below, the steps I had planned at the end of the first semester:
Implement PlatformIO[1] to connect the Arduino´s codes together and have a better and more fluent programming environment;
create a GUI that communicates with the instrument via Wi-Fi. Through OSC messages, I will map the following parameters:
the time interval between the beats of the solenoid;
velocity;
the degrees of rotation of the lever to vary the pitch;
the degrees of rotation of the tuning screws;
build two wooden sticks to support two hammers for each string.
change the tuning system of the “Hackbrett”, similar to a guitar´s one, to decrease the required torsion force for the DC motor to rotate them;
create different supports that fits the servos in order to change the tuning of the strings;
regarding the performative aspect of this instrument, I will implement one IR sensor to control the lever. I will map the movement of the hand to the steps of the motor to change the pitch through movement.
implement a small DC motor to control a sort of mute rail of the piano, damping the strings.
[1] PlatformIO Platformio is a professional collaborative platform for embedded development, PlatformIO. Available at: https://platformio.org/ (Accessed: January 26, 2023).
In order to effectively showcase the individual components that would eventually comprise the final instrument, I took the initiative to create a rudimentary version resembling a Hackbrett, utilizing a wooden board and a Floyd Rose tremolo system. This makeshift instrument boasted the inclusion of two strings and a mobile bridge, enabling the manipulation of string pitch without the need for mechanical screws.
To emulate the motion of drumsticks required to play the instrument, I employed two piano hammers (Fig. 2) upon which I strategically positioned the two solenoids. These solenoids were connected to the structure through the help of a wooden stick, which also served as a housing for all the necessary electronic components (Fig. 1), ensuring a compact and conveniently transportable design. The resultant outcome was an instrument that facilitated effortless customization, thanks of its adaptable elements capable of being repositioned in space, thereby opening up a realm of diverse tonal possibilities to be explored.
The decision to use wood as the primary material for the instrument was driven by its acoustic characteristics. Even without the presence of a resonance chamber, wooden material offered a sound quality that closely resembled the desired outcome of the final product.
To capture the sound produced by the strings, I opted for an electric piezo system. This allowed for the isolation of the direct string sound from the mechanical sound generated by the solenoids. By employing this setup, I could accurately capture the nuances of the instrument’s natural vibrations while maintaining control over the mechanical elements. To amplify it, I mounted a speaker on a wooden plate that should has work as resonator. The entire amplification id driven by a D-Class amplifier PAM480[1], attached with the speaker directly on the body of the instrument (Fig. 3).
By fixing the Floyd Rose lever (Fig. 4) in conjunction with the stepper motor, I devised a solution using two small wooden pieces that served as a guide for the lever. This setup ensured that the lever remained stable and fixed during the tensioning process. Strategically positioning the stepper motor directly at the tip of the lever was a deliberate choice aimed at maximizing the advantage of leverage. By identifying the optimal leverage point, I could effectively exert tension on the strings with minimal effort from the stepper motor.
Regarding the use of the Servo motor, the idea is to simulate a feature of the final instrument that will be applied during the next semester, i.e. a mute that can attenuate the strings. As can be seen in Fig. 5, the pedals are connected by a string to a wooden rod and felt, which acts as a mute if necessary.
[1] GmbH, B. 73 A. (no date) Startseite, Startseite • FUNKAMATEUR OnlineShop. Available at: https://www.box73.de/product_info.php?products_id=4391 (Accessed: 15 June 2023).
