Spatial Acoustics: The Ultrasonic Theremin

ABSTRACT:

This project focuses on designing and developing an instrument for producing music that does not require physical keys to operate. The goal of this project is to create a user friendly interface that will enable musicians to create a music without the need for a traditional methods. The keyless musical instrument is designed to be used by musicians of any level from beginner to professional.

Playing a piano requires pressing physical buttons locked into explicit octaves. The Keyless Musical Instrument replicates the bizarre and terrifying Russian "Theremin" from the 1920s entirely utilizing digital silicon! Instead of radio waves, this instrument utilizes explosive bursts of Ultrasonic sound. The Arduino generates an acoustic wall out of an HC-SR04 sensor. As the user's empty hand approaches or retreats in mid-air, the Arduino violently intercepts the shifting distance metrics and instantly executes complex mathematical equations, scaling the physical centimeters natively into pure audible frequency sweeps via a Piezo Buzzer!

OBJECTIVE:

IT IS USED FOR PLAYING MUSIC WITHOUT ANY KEYS IT DISPLAYS THE MUSIC NOTES IT WILL ALSO DISPLAY THE OCTAVE WHICH WE ARE PLAYING OCTAVE CAN BE CHANGED FROM OCTAVE 3 TO OCTAVE 7

METHODOLOGY:

The keys or strings are replaced by 8 laser lights. Each laser beam will hit their specific photoresistors (LDR-Light Dependent Resistor). While interrupting the laser beam, the photoresistor will give output signal to the Arduino, then Arduino will produce the specific tone by speaker through amplifier, by which music can be produced. We are placing LCD display to display the music note and octave which we are playing. Here we are placing the rotary encoder for changing the octaves, the octave can be tuned from octave 3 to octave 7 by tuning the rotary encoder.

Converting Centimeters into Frequencies (map())

The core engine relies heavily upon translating spatial metrics (e.g., 5cm to 30cm) into audible Hertz (e.g., 200Hz to 1500Hz).

1. The SR04 fires its 40Khz pulse, extracting the distance variable.
2. The Arduino utilizes its massive built-in map() mathematics function!
3. int note = map(distance, 5, 30, 200, 1500);
4. The moment the distance drops below 5cm or goes past 30cm, the Arduino must explicitly kill the note to prevent horrifying static anomalies (noTone()).

int distance = getDistance(); // Returns the exact CM measurement!

if (distance >= 5 && distance <= 30) {
  // Constrain limits to prevent bizarre glitches!
  int rawFreq = map(distance, 5, 30, 261, 1046); // Map CM into Middle C up to High C!
  
  // Fire the hardware Timer array to generate the explicit square wave Hz!
  tone(BUZZER_PIN, rawFreq); 
} else {
  // Silence! Hand is outside the play area!
  noTone(BUZZER_PIN); 
}

// Intense delay limits the math loop so the tone isn't constantly stuttering!
delay(40); 

Overcoming Square Wave Audio Distortion

The Arduino tone() function produces an incredibly harsh, aggressive, mathematically perfect Square Wave. It sounds like a cheap 1980s microwave alarm, not a smooth violin!

• To soften the audio, you use a physical Low-Pass Filter Capacitor!
• By violently wiring a 0.1µF or 1µF Electrolytic Capacitor directly across the positive and negative legs of the Piezo or 8-Ohm speaker, it physically absorbs the ultra-sharp high-frequency electric spikes, rounding off the harsh edges of the Square Wave into something resembling a pseudo-Sine Wave naturally!

Acoustical Hardware Matrices

• Arduino Uno/Nano (Executing the massive hardware frequency timers continuously).
• HC-SR04 Ultrasonic Sensor (Must face unobstructed completely upwards or outwards in empty space).
• Passive Piezo Buzzer or 8-Ohm Mini Speaker (Wait! An Active Buzzer will FAIL completely; it only makes a single predetermined annoying beep! You absolutely MUST use a "Passive" Buzzer which acts like an empty speaker capable of playing varying frequencies!).
• Low-Pass Filter Capacitor (Usually completely optional, but critical for professional synthesizer clarity).

WORKING VIDEOS:

https://youtube.com/shorts/sBYvBHOLajY?si=_F3S_4xVVtGr7GOg

IMAGES: