3.3 Air Piano

Normally, when we play a musical instrument, we have to pluck strings or press keys to produce musical notes. However, with electronic modules, playing music can become more exciting. For instance, you can simulate piano playing with push-button switches and even integrate light effects for interactive music. But if you use push-button switches as piano keys, you need to integrate many modules into the circuit. Is there a simpler and more unique idea? A combination of ultrasonic distance sensor and passive buzzer can do just that - detecting different distances with ultrasonics to trigger different notes, just like playing a piano in the air.

3.3.1 Background Knowledge

3.3.1.1 Grove Ultrasonic Distance Sensor

The Grove Ultrasonic Distance Sensor is a non-contact distance measurement module. Thanks to its strong directivity, the ultrasonic waves it emits can travel long distances in a medium. The calculations are simple and it is easy to control, so it’s often used for distance measurements. When the ultrasonic distance sensor works, the transmitter emits ultrasonic waves in a certain direction. When the waves hit an obstacle, they reflect back. The ultrasonic receiver stops timing as soon as it receives the reflected waves. The actual distance from the emission point to the obstacle is calculated based on the time difference between emission and reception, much like bat echolocation. The application range of ultrasonic waves is becoming broader, commonly seen in reverse radar systems, intelligent guidance systems, robot obstacle avoidance systems, medical ultrasound examinations, and more.

⚠️ Note
The Grove Ultrasonic Distance Sensor module is not included in the Seeed Studio XIAO Starter Kit!

3.3.2 Task 1: Reading the Grove Ultrasonic Distance Sensor Value

Adding the Seeed_Arduino_UltrasonicRanger Library

Before starting to program the Grove Ultrasonic Distance Sensor with Arduino IDE, it’s necessary to add the essential library for the sensor. Type the library address 🔗 https://github.com/Seeed-Studio/Seeed_Arduino_UltrasonicRanger into the browser address bar, enter the GitHub page, click Code→Download ZIP to download the resource package Seeed_Arduino_UltrasonicRanger-master.zip to your local drive, as shown below.

Add the downloaded resource package Seeed_Arduino_UltrasonicRanger-master.zip to the Sketch→Include Library→Add .ZIP Library from the menu bar until you see a successful library loading prompt.

Opening the Example File

After successfully installing the library, a new item Grove Ultrasonic Ranger will be added to the Arduino’s File→Examples list. Open the UltrasonicDisplayOnTerm sample program from it. This program can display the value of the ultrasonic distance sensor on the Serial Monitor. Modify Ultrasonic ultrasonic(7); in the sample program to Ultrasonic ultrasonic(0); (the ultrasonic distance sensor will be connected to the A0 port of the XIAO expansion board).

Open the modified sample file through the following path, 🔗
https://github.com/mouseart/XIAO-Mastering-Arduino-and-TinyML/tree/main/code/L13_UltrasonicDisplayOnTerm_XIAO_en.

#include "Ultrasonic.h"//declare the library file
Ultrasonic ultrasonic(0);//define variables, connect pins. If you're using XIAO RP2040/XIAO ESP32, please change 0 to D0
void setup() {
    Serial.begin(9600);
}
void loop() {
    long RangeInInches;//define a long integer variable named RangeInInches
    long RangeInCentimeters;//define a long integer variable named RangeInCentimeters

    Serial.println("The distance to obstacles in front is: ");
    RangeInInches = ultrasonic.MeasureInInches();//read the distance value (inches) measured by the ultrasonic distance sensor and store it in the variable RangeInInches
    Serial.print(RangeInInches);//serial print value
    Serial.println(" inch");
    delay(250);

    RangeInCentimeters = ultrasonic.MeasureInCentimeters(); //read the distance value (centimeters) measured by the ultrasonic distance sensor and store it in the variable RangeInCentimeters
    Serial.print(RangeInCentimeters);//serial print value
    Serial.println(" cm");
    delay(250);
}

The ultrasonic distance sensor is connected to the A0 interface, as shown in the figure below:

After uploading the code, open the Serial Monitor. Place your hand or a card at any position in front of the ultrasonic distance sensor and observe the change in the values output by the Serial Monitor.

3.3.3 Project Production: Ultrasonic Air Harp

Project Description

The working principle of the air harp is to measure the distance from the module to the palm of your hand through the ultrasonic distance sensor. Depending on the distance, the buzzer emits different musical notes. We have already learned how to measure distance and read values through the ultrasonic distance sensor with the sample program. Next, we just need to define different musical notes for the corresponding distances. As shown in the figure below: According to the width of the palm, one musical note corresponds to a unit of 2cm, and the performance starts from 4cm. “Do, Re, Mi, Fa, Sol, La, Xi, Do” respectively correspond to 4cm, 6cm, 8cm, 10cm, 12cm, 14cm, 16cm, 18cm… and so on.

Writing the Program

The implementation of the air harp program requires the following steps:

• Declare the library file, define different notes and buzzer pins.
• Initialization, setting the status of the buzzer pin.
• Read the distance (cm) measured by the ultrasonic distance sensor, and make a condition judgment to set different distances to emit different notes.

Using the tone() Function to Play Melody

When we want to control the buzzer to play notes or songs through the program, we need to set the frequency value of each note ourselves. If a song has many notes, it’s too troublesome to adjust one by one, and it tests our music theory knowledge and pitch. Is there a simpler method? Of course! When defining notes, we can refer to the tone() function written on the Arduino website 🔗 https://www.arduino.cc/en/Tutorial/BuiltInExamples/toneMelody, this function defines the corresponding frequency of different notes through pitches.h, which is convenient for us to use the tone() function to set the notes emitted by the buzzer. The code of pitches.h is shown below:

/*
* pitches.h
*/

#define NOTE_B0  31
#define NOTE_C1  33
#define NOTE_CS1 35
#define NOTE_D1  37
#define NOTE_DS1 39
#define NOTE_E1  41
#define NOTE_F1  44
#define NOTE_FS1 46
#define NOTE_G1  49
#define NOTE_GS1 52
#define NOTE_A1  55
#define NOTE_AS1 58
#define NOTE_B1  62
#define NOTE_C2  65
#define NOTE_CS2 69
#define NOTE_D2  73
#define NOTE_DS2 78
#define NOTE_E2  82
#define NOTE_F2  87
#define NOTE_FS2 93
#define NOTE_G2  98
#define NOTE_GS2 104
#define NOTE_A2  110
#define NOTE_AS2 117
#define NOTE_B2  123
#define NOTE_C3  131
#define NOTE_CS3 139
#define NOTE_D3  147
#define NOTE_DS3 156
#define NOTE_E3  165
#define NOTE_F3  175
#define NOTE_FS3 185
#define NOTE_G3  196
#define NOTE_GS3 208
#define NOTE_A3  220
#define NOTE_AS3 233
#define NOTE_B3  247
#define NOTE_C4  262
#define NOTE_CS4 277
#define NOTE_D4  294
#define NOTE_DS4 311
#define NOTE_E4  330
#define NOTE_F4  349
#define NOTE_FS4 370
#define NOTE_G4  392
#define NOTE_GS4 415
#define NOTE_A4  440
#define NOTE_AS4 466
#define NOTE_B4  494
#define NOTE_C5  523
#define NOTE_CS5 554
#define NOTE_D5  587
#define NOTE_DS5 622
#define NOTE_E5  659
#define NOTE_F5  698
#define NOTE_FS5 740
#define NOTE_G5  784
#define NOTE_GS5 831
#define NOTE_A5  880
#define NOTE_AS5 932
#define NOTE_B5  988
#define NOTE_C6  1047
#define NOTE_CS6 1109
#define NOTE_D6  1175
#define NOTE_DS6 1245
#define NOTE_E6  1319
#define NOTE_F6  1397
#define NOTE_FS6 1480
#define NOTE_G6  1568
#define NOTE_GS6 1661
#define NOTE_A6  1760
#define NOTE_AS6 1865
#define NOTE_B6  1976
#define NOTE_C7  2093
#define NOTE_CS7 2217
#define NOTE_D7  2349
#define NOTE_DS7 2489
#define NOTE_E7  2637
#define NOTE_F7  2794
#define NOTE_FS7 2960
#define NOTE_G7  3136
#define NOTE_GS7 3322
#define NOTE_A7  3520
#define NOTE_AS7 3729
#define NOTE_B7  3951
#define NOTE_C8  4186
#define NOTE_CS8 4435
#define NOTE_D8  4699
#define NOTE_DS8 4978

Task 2: Ultrasonic Air Harp

Step 1: Declare the library file, define different notes and buzzer pins. The main notes we use are “Do Re Mi Fa Sol La Xi Do”, corresponding to “C5 D5 E5 F5 G5 A5 B5 C6”. You can only define the notes you need to avoid the program looking too lengthy.

#include "Ultrasonic.h"//declare the library file
Ultrasonic ultrasonic(0);//define the ultrasonic object and connect the ultrasonic wave to the A0 interface. If you're using XIAO RP2040, please change 0 to D0
int buzzerPin = 3;//The buzzer is connected to the A3 interface, if you're using XIAO RP2040, please change 3 to A3

#define NOTE_C5  523
#define NOTE_CS5 554
#define NOTE_D5  587
#define NOTE_DS5 622
#define NOTE_E5  659
#define NOTE_F5  698
#define NOTE_FS5 740
#define NOTE_G5  784
#define NOTE_GS5 831
#define NOTE_A5  880
#define NOTE_AS5 932
#define NOTE_B5  988
#define NOTE_C6  1047

Step 2: Initialize the baud rate and set the buzzer pin status.

void setup()
{
    Serial.begin(9600);
    pinMode(buzzerPin,OUTPUT);
}

Step 3: Read the distance (cm) measured by the ultrasonic distance sensor and make a condition judgment to set different distances to emit different notes. Since the setting of the air harp is that different distances trigger different notes, and this distance is a long integer value, so we need to use the long() function to define the value returned by the ultrasonic wave. For example, (long)RangeInCentimeters== 4, that is, the distance value returned by the ultrasonic wave is 4. Corresponding to the buzzer emitting different notes, use the tone() function, for example, tone(3,NOTE_C5,100), that is, the buzzer on pin 3, emits NOTE_C5 (Do) note, lasts for 100 milliseconds.

void loop()
{
    // Read the distance value detected by the ultrasonic distance sensor, in centimeters, and print it on the serial monitor
    long RangeInCentimeters;
    RangeInCentimeters = ultrasonic.MeasureInCentimeters(); 
    Serial.print(RangeInCentimeters);
    Serial.println(" cm");
    delay(250);
    // Using an if statement for conditional judgment, when the distance is 4, 6, 8, 10, 12, 14, 16, 18, it corresponds to C5, D5, E5, F5, G5, A5, B5, C6
    if (((long)RangeInCentimeters== 4)) {  //Do
        tone(3,NOTE_C5,100);   
    }
    if (((long) RangeInCentimeters== 6)) { //Re
        tone(3,NOTE_D5,100);    
    }
    if (((long) RangeInCentimeters== 8)) { //Mi
        tone(3,NOTE_E5,100);  
    }
    if (((long) RangeInCentimeters== 10)) {  //Fa
        tone(3,NOTE_F5,100);
    }
    if (((long) RangeInCentimeters== 12)) {  //Sol
        tone(3,NOTE_G5,100);
    }
    if (((long) RangeInCentimeters== 14)) {  //La
        tone(3,NOTE_A5,100);
    }
    if (((long) RangeInCentimeters== 16)) { //Xi
        tone(3,NOTE_B5,100);
    }
    if (((long) RangeInCentimeters== 18)) {  //Do
        tone(3,NOTE_C6,100);
    }
}

Get this program from Github
https://github.com/mouseart/XIAO-Mastering-Arduino-and-TinyML/tree/main/code/L13_UltrasonicPiano_XIAO_en

Step 4: Connect the hardware and upload the program. Connect the ultrasonic distance sensor to the A0 interface of the XIAO expansion board as shown below:

Use the data cable to connect XIAO to the computer, click the “Upload” button, upload the program to the hardware, when the debugging area shows “Upload Successful”, open the serial monitor, and start playing with your palm.

3.3.4 Exterior Design

The inspiration for the air harp comes from the piano, with a note every 2 cm also designed according to the style of the piano keys. In the process of creating the appearance, we can cut a harp surface from a basswood board, and fix the ultrasonic range sensor at the left end of the harp. We also provide laser cutting files for reference, which can be easily assembled, as shown in the picture:

Download the files suitable for the laser cutting machine 🔗
https://github.com/mouseart/XIAO-Mastering-Arduino-and-TinyML/blob/main/dxf/XIAO_Air_Piano.dxf.