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Tone Output using an Arduino

Overview

This lab is an introduction to generating simple tones on an Arduino. NOTE: This will work only for Arduino 0018 and beyond. For previous versions, use Brett Hagman's Tone library (:toc Table of Contents:)

Parts

For this lab you'll need:

Solderless breadboard
Solderless breadboard
hookup wire
22-AWG hookup wire
Arduino module
Arduino Microcontroller
module


resistors
1Kohm resistors
photocell
photocell
(or a different
form of variable resistor)
speaker
8-ohm speaker


Why not use AnalogOut()?

When you use analogOut() 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 analogOut(), 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 power and ground from the microcontroller. On the Arduino module, use the 5V and any of the ground connections:


(Diagram 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.


(Diagram made with Fritzing)

NOTE: this sensor circuit is not the normal way of connecting an analog input. There is no fixed resistor. The two photocells act as a voltage divider together, ao 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
}

Note the range that the sensors give you by alternately covering them up and giving them full light, with the serial monitor window all the time. You'll need the maximum and minimum sensor values for the next sketch.

Play Tones

Write a sketch to read the analog input and map the result to a range from 100 to 1000. 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.


/*************************************************
* Public Constants
*************************************************/


/*************************************************
* Public Constants
*************************************************/


 #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

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 follows (in C Major):


image from seventhstring.com

or:

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!

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:

The circuit:

This circuit uses the more traditional voltage divider circuit.

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.

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