Lab 5: Tone Output Using An Arduino

Introduction

This lab is an introduction to generating simple tones on an Arduino. In order to make the most of this lab, you should understand the basics of how to program digital input and output on an Arduino, and how to read a simple circuit diagram.

Video of this lab

What You’ll Need

Figures 1-7 below show the parts you’ll need for this exercise. Click on any image for a larger view.

Photo of an Arduino Nano 33 IoT module. The USB connector is at the top of the image, and the physical pins are numbered in a U-shape from top left to bottom left, then from bottom right to top right.
Figure 1. Microcontroller. Shown here is an Arduino Nano 33 IoT
Photo of flexible jumper wires
Figure 2. Jumper wires.  You can also use pre-cut solid-core jumper wires.
Photo of a solderless breadboard
Figure 3. A solderless breadboard
Photo of an 8 ohm speaker
Figure 4. An 8 ohm speaker (optional).This is a good alternate to the LED if you prefer audible output.
Photo of a handful of 220-ohm resistors.
Figure 5. 100-ohm to 220-ohm resistors. The ones shown here are  are 4-band 220-ohm resistors. They are colored red, red, brown and gold, which signifies 2, 2 (red, red), times 10 (brown), with a 5% tolerance (gold).
Photo of a handful of 10-kilohm resistors
Figure 6. 10-kilohm resistors. These ones are 5-band resistors. They are colored brown, black, black, red, brown, which signifies 1 (brown), 0, 0 (black, black), times 100 (red), with a 1% tolerance (brown). Four-band 10-kilohm resistors are colored brown, black, orange (1, 0, times 1000), gold (5% tolerance).
Photo of a Force Sensing Resistor (FSR)
Figure 7. Force Sensing Resistor (FSR) or any variable resistor. Note that one circuit in this lab does not work with phototransistors.

Why not use analogWrite()?

When you use analogWrite() to create pulsewidth modulation (PWM) on an output pin, you can change the on-off ratio of the output (also known as the duty cycle) but not the frequency. If you have a speaker connected to an output pin running analogWrite(), you’ll get a changing loudness, but a constant tone. To change the tone, you need to change the frequency. The tone() command does this for you.

Prepare the breadboard

Connect power and ground on the breadboard to the microcontroller. On the Arduino module, use the 5V or 3.3V (depending on your model) and any of the ground connections. Figures 8 and 9 show connections for an Arduino Uno and a Nano, respectively.

An Arduino Uno on the left connected to a solderless breadboard, right. The Uno's 5V output hole is connected to the red column of holes on the far left side of the breadboard. The Uno's ground hole is connected to the blue column on the left of the board. The red and blue columns on the left of the breadboard are connected to the red and blue columns on the right side of the breadboard with red and black wires, respectively. These columns on the side of a breadboard are commonly called the buses. The red line is the voltage bus, and the black or blue line is the ground bus.

Figure 8. An Arduino Uno on the left connected to a solderless breadboard, right. The Uno’s 5V output hole is connected to the red column of holes on the far left side of the breadboard. The Uno’s ground hole is connected to the blue column on the left of the board. The red and blue columns on the left of the breadboard are connected to the red and blue columns on the right side of the breadboard with red and black wires, respectively. These columns on the side of a breadboard are commonly called the buses. The red line is the voltage bus, and the black or blue line is the ground bus.

Arduino Nano on a breadboard.

Figure 9. An Arduino Nano mounted on a solderless breadboard. The Nano is mounted at the top of the breadboard, straddling the center divide, with its USB connector facing up. The top pins of the Nano are in row 1 of the breadboard.

The Nano, like all Dual-Inline Package (DIP) modules, has its physical pins numbered in a U shape, from top left to bottom left, to bottom right to top right. The Nano’s 3.3V pin (physical pin 2) is connected to the left side red column of the breadboard. The Nano’s GND pin (physical pin 14) is connected to the left side black column. These columns on the side of a breadboard are commonly called the buses. The red line is the voltage bus, and the black or blue line is the ground bus. The blue columns (ground buses) are connected together at the bottom of the breadboard with a black wire. The red columns (voltage buses) are connected together at the bottom of the breadboard with a red wire.

Images made with Fritzing

Connect the Sensors and the Speaker

Connect two photoresistors to analog pin 0 in a voltage divider circuit as shown below. The 8-ohm speaker connects to pin 8 of the Arduino. You can use any digital I/O pin if you don’t like 8. The other end of the speaker connects to ground. Figures 10 through 12 show the schematic drawing and the breadboard layouts for an Uno and a Nano, respectively.

Note: Although the circuit shown in Figures 10-12 has a 100-ohm resistor with the speaker, you can use a larger resistor. The larger the resistor, the quieter the speaker. A 220-ohm resistor works reasonably well if you don’t have a 100-ohm resistor.

 

Schematic view of an Arduino connected to two force sensing resistors (FSRs) and a speaker.
Figure 10. Schematic view of an Arduino connected to two force sensing resistors (FSRs) and a speaker. One leg of the first FSR is connected to voltage. The other leg is connected simultaneously to the first leg of the second FSR and the Arduino’s analog input pin A0. The second leg of the FSR is connected to ground. The red positive wire of the speaker is connected to digital pin 8 of the Arduino. The black ground wire of the speaker is connected to one leg of a 100 ohm resistor. The other leg of the resistor connects to ground.

 

Breadboard view of an ArduinoNano connected to two force sensing resistors (FSRs) and a speaker.
Figure 11. Breadboard view of an Arduino connected to two force-sensing resistors and a speaker. The Arduino’s voltage out and ground pins are connected to the voltage and ground buses of the breadboard as usual. The FSRs are mounted in the left center section of the breadboard. One leg of the first FSR is connected to 5 volts. The other leg is connected simultaneously to the first leg of the second FSR and the Arduino’s analog input pin A0. The second leg of the second FSR is connected to ground. The red positive wire of the speaker is connected to digital pin 8 of the Arduino. The black ground wire of the speaker is connected to one leg of a 100 ohm resistor. The other leg of the resistor connects to ground.
Breadboard view of an Arduino Nano connected to two force sensing resistors (FSRs) and a speaker.
Figure 12. Breadboard view of an Arduino Nano connected to two force sensing resistors (FSRs) and a speaker. The Nano’s 3.3 Volts (physical pin 2) and ground (physical pin 14) are connected to the voltage and ground buses of the breadboard as usual. The FSRs are mounted below the Nano in the left center section of the breadboard. One leg of the first FSR is connected to voltage. The other leg is connected simultaneously to the first leg of the second FSR and the Arduino’s analog input pin A0. The second leg of the second FSR is connected to ground. The red positive wire of the speaker is connected to digital pin 8 of the Arduino. The black ground wire of the speaker is connected to one leg of a 100 ohm resistor. The other leg of the resistor connects to ground.

NOTE: this sensor circuit is not the normal way of connecting an analog input. There is no fixed resistor. The two force sensing resistors act as a voltage divider together, so you can change the value of the analog in by covering either one. if you are using variable resistors that can both go to 0 ohms, you should connect a fixed resistor in series from the junction of the two resistors to the input, to avoid a short.

Check the sensor input range

Once you’ve got the circuit connected, check the range of the analog input and note the highest and lowest values you can reach.

void setup() {
  Serial.begin(9600);       // initialize serial communications
} 

void loop()
{
  int analogValue = analogRead(A0); // read the analog input
  Serial.println(analogValue);      // print it
}

Play Tones

Write a sketch to read the analog input and map the result to a range from 100 to 1000. The example below assumes your analog input circuit ranges from 200 to 900, so adjuct for your actual values.  Store the result in a local variable called frequency. This will be the frequency you play on the speaker Then use the tone() command to set the frequency of the speaker on pin 8.

void setup() {
    // nothing to do here
 }

 void loop() {
   // get a sensor reading:
   int sensorReading = analogRead(A0);
   // map the results from the sensor reading's range
   // to the desired pitch range:
   float frequency = map(sensorReading, 200, 900, 100, 1000);
   // change the pitch, play for 10 ms:
   tone(8, frequency, 10);
 }

Once you’ve uploaded this, move your hands over the photocells, and listen to the frequency change. It will change from 100 Hz to 1000 HZ, because that’s what you set in the map() command. If you want to change the frequency range, change those two numbers. See if you can get it to play a little tune.

A more complex example

The pitches.h file includes constants that give you the pitches for a standard western scale. To include them in your sketch, click the New Tab button on the toolbar and create a new tab called pitches.h. Then copy the file below and paste it in the new tab in your sketch. Figure 13 shows the new Tab dropdown menu.

A dropdown menu located in the upper right hand corner of the Arduino IDE. In order the options are "New Tab", "Rename", "Delete", "Previous Tab", "Next Tab", and the last option shows the name of the sketch
Figure 13. A dropdown menu located in the upper right hand corner of the Arduino IDE showing the tab options. You can also type cmmand-shift-N to get a new tab.

For this sketch, you’ll play a simple melody. A melody consists of notes played in a sequence, and rests between the note. Each note and rest has its own particular duration. You’re going to play a seven note sequence, as shown in Figure 14 (in C Major):

Two measures of a musical notation in 4 / 4 time. The notes are C4, G3, G3, G#3, G3,rest, B3, C4 the respective durations are: quarter note, eighth note, eighth note, quarter note, quarter note, quarter rest, quarter note, quarter note
Figure 14. Two measures of a musical notation. The melody is “Shave and a haircut, two bits”

image from seventhstring.com

The sequence is: C4, G3, G3, G#3, G3, rest, B3, C4

the durations are:

quarter note, eighth note, eighth note, quarter note, quarter note, quarter rest, quarter note, quarter note. 

Start your sketch with two global variables. Using pitches.h, make an array variable holding those notes. Make a second array to hold the note durations, marking quarter notes as 4 and eighth notes as 8.

// notes in the melody:
 int melody[] = {
   NOTE_C4, NOTE_G3,NOTE_G3, NOTE_GS3, NOTE_G3,0, NOTE_B3, NOTE_C4};

 // note durations: 4 = quarter note, 8 = eighth note, etc.:
 int noteDurations[] = {
   4, 8, 8, 4,4,4,4,4 };

How can you use the durations to play notes? Well, imagine that a quarter note is one quarter of a second, and eighth note is one eighth of a second, and so forth. In that case, the actual duration for each note is 1000 milliseconds divided by the value for it in the durations array. For example, the first note is 1000/4, the second is 1000/8, and so forth.

Now, you only want to play the song once, so everything will happen in the setup(). Make a for loop in the setup to iterate over the seven notes. For each time through the loop, use tone() to play the next note in the array. Use the formula in the last paragraph to determine how long each note should play for. After you start the note, delay for as long as the note plays, plus 30 milliseconds or so, to separate each note.

 #include "pitches.h"

 // notes in the melody:
 int melody[] = {
   NOTE_C4, NOTE_G3,NOTE_G3, NOTE_GS3, NOTE_G3,0, NOTE_B3, NOTE_C4};

 // note durations: 4 = quarter note, 8 = eighth note, etc.:
 int noteDurations[] = {
   4, 8, 8, 4,4,4,4,4 };

 void setup() {
   // iterate over the notes of the melody:
   for (int thisNote = 0; thisNote < 8; thisNote++) {

     // to calculate the note duration, take one second
     // divided by the note type.
     //e.g. quarter note = 1000 / 4, eighth note = 1000/8, etc.
     int noteDuration = 1000/noteDurations[thisNote];
     tone(8, melody[thisNote],noteDuration);

     //pause for the note's duration plus 30 ms:
     delay(noteDuration +30);
   }
 }

 void loop() {
   // no need to repeat the melody.
 }

That’s the whole tune! Next, try making a musical instrument.

A Musical Instrument

Playing a tune like you just doesn’t allow for much user interaction, so you might want to build more of a musical instrument.

Here’s an example of how to use the note constants to make a simple keyboard. Figures 15 -17  show the circuit.

Schematic view of an Arduino connected to three force sensing resistors (FSR) and a speaker. Each of the three FSRs have one of their respective legs connected to +5 volts. Each of the other legs connect to one leg of a 10-kilohm resistor and simultaneously connect to one of the Arduino's analog input pins. In this case the pin connections are A0, A1, and A2. Each of the respective 10-kilohm resistors then connect to ground. The red positive wire of the speaker is connected to digital pin 8 of the Arduino. The black ground wire of the speaker is connected to one leg of a 100 ohm resistor. The other leg of the 100-ohm resistor connects to ground.
Figure 15. Schematic view of an Arduino connected to three force sensing resistors and a speaker.
Breadboard view of an Arduino connected to three force sensing resistors (FSR) and a speaker. Each of the three FSRs have one of their respective legs connected to +5 volts. Each of the other legs connect to one leg of a 10-kilohm resistor and simultaneously connect to one of the Arduino's analog input pins. In this case the pin connections are A0, A1, and A2. Each of the respective 10-kilohm resistors then connect to ground. The red positive wire of the speaker is connected to digital pin 8 of the Arduino. The black ground wire of the speaker is connected to one leg of a 100 ohm resistor. The other leg of the 100 ohm resistor then connects to ground.
Figure 16. Breadboard view of an Arduino connected to three force sensing resistors (FSR) and a speaker. Each of the three FSRs have one of their respective legs connected to +5 volts. Each of the other legs connect to one leg of a 10-kilohm resistor and simultaneously connect to one of the Arduino’s analog input pins. In this case the pin connections are A0, A1, and A2. Each of the respective 10-kilohm resistors then connect to ground. The red positive wire of the speaker is connected to digital pin 8 of the Arduino. The black ground wire of the speaker is connected to one leg of a 100 ohm resistor. The other leg of the 100 ohm resistor then connects to ground.

Breadboard view of an Arduino Nano connected to three force sensing resistors (FSR) and a speaker.Figure 17. Breadboard view of an Arduino Nano connected to three force sensing resistors (FSR) and a speaker. Each of the three FSRs have one of their respective legs connected to the voltage bus of the breadboard. Each of the other legs connect to one leg of a 10-kilohm resistor and simultaneously connect to one of the Arduino’s analog input pins. In this case the pin connections are A0, A1, and A2. Each of the respective 10-kilohm resistors then connect to ground. The red positive wire of the speaker is connected to digital pin 8 of the Arduino. The black ground wire of the speaker is connected to one leg of a 100 ohm resistor. The other leg of the 100 ohm resistor then connects to ground.

 

Program it

Make a sketch that plays a note on each sensor when the sensor is above a given threshold.

Start with a few constants: one for the threshold, one for the speaker pin number, and one for the duration of each tone. To make this instrument work, you need to know what note corresponds to each sensor. Include pitches.h as you did above, then make an array that contains three notes, A4, B4, and C3 as well. Set all of this up at the beginning of your sketch, before setup().

#include "pitches.h"

const int threshold = 10;      // minimum reading of the sensors that generates a note
const int speakerPin = 8;      // pin number for the speaker
const int noteDuration = 20;   // play notes for 20 ms

// notes to play, corresponding to the 3 sensors:
int notes[] = {
  NOTE_A4, NOTE_B4,NOTE_C3 };

You don’t need anything in your setup(), but in your loop, you need a for loop that iterates over the first three analog inputs, 0, 1, and 2. For each one, read the sensor, and if it’s above a threshold, play the corresponding note in the notes array for the note duration.

#include "pitches.h"

const int threshold = 10;      // minimum reading of the sensors that generates a note
const int speakerPin = 8;      // pin number for the speaker
const int noteDuration = 20;   // play notes for 20 ms

// notes to play, corresponding to the 3 sensors:
int notes[] = {
  NOTE_A4, NOTE_B4,NOTE_C3 };

void setup() {

}

void loop() {
  for (int thisSensor = 0; thisSensor < 3; thisSensor++) {    

// get a sensor reading:
int sensorReading = analogRead(thisSensor);     

// if the sensor is pressed hard enough:
if (sensorReading > threshold) {

// play the note corresponding to this sensor:
      tone(speakerPin, notes[thisSensor], 20);
    }
  }
}

When you upload this sketch, you should have a three-key keyboard.

Get Creative

This is just a suggestion for a short project. It’s not a requirement for the class homework.

Now that you’ve got the basics, make a musical instrument. Consider a few things in designing yor instrument:

  • Do you want to play discrete notes (like a piano), or sliding pitches (like a theremin)? How do you program to achieve these effects?
  • Do you want to control the tempo and duration of a note?
  • Do you want the same physical action to set both the pitch and the velocity (volume) of a note?
  • Do you want to be able to play more than one note at a time (e.g. chords)?

All of these questions, and many more, will affect what sensors you use, how you read them, and how you design both the physical interface and the software.

Originally written on July 10, 2014 by Tom Igoe
Last modified on August 2, 2019 by Tom Igoe