3 min read

Week 2: Why Won't This Speaker Work?! Because I Need Delay!

Week 2 Notes
Background Microcontrollers: Input: sensor; output: actuator GPIO: general purpose input and output Microcontroller: a simple (firmware only) processor, vs. OS processor Embedded/central processor: runs an OS from external storage (Raspberry Pi) Needs a voltage regulator and crystal (clock) Firm...
See notes on labs and textbook readings here.

Idea: Create an instrument using 8 push buttons corresponding to each note in a scale, a speaker, and the Arduino to assign different frequency pitches when each button is pressed. As an extension, change the key of the instrument by turning a potentiometer up or down.

Reality: My speaker won’t even play one note! What is wrong with my circuit?

An Arduino connected to a push button, which in turn connects to both a 10kΩ resistor that leads to ground as well as D9. Another wire connects D10 to a speaker, which follows a 220Ω resistor to ground.
A breadboard visualization of the circuit described above. 

I wrote the following code for this section of the circuit:

const int outputPin = 10;
int frequency = 850;
void setup() {
  pinMode(9, INPUT);
  pinMode(outputPin, OUTPUT);
void loop() {
  if (digitalRead(9) == HIGH) {
    tone(outputPin, frequency);
  } else {

As a check, I replaced the speaker with a red LED, and changed the code so that instead of the tone() and noTone() functions, I used digitalWrite(). The circuit works as expected:

A red LED lights up on the circuit board while pressing a button.

Why doesn’t the circuit work with a speaker? After trying out a few things with Elias, I found out that adding a few milliseconds of delay will do the trick. But why do we need delay to produce sound?

if (digitalRead(9) == HIGH) {
    tone(outputPin, 523);

Anyway, since my instrument is basically a group of buttons, I can repeat the same logic above for the rest. Is it possible to simplify the circuit? For example, I currently have a 10kΩ resistor connected to each push button, but if I connect all of the ends, can I use just one?

And how much more can I simplify the code? If there are arithmetic relationships between each note in a scale, I can just calculate it, allowing the user to potentially tune the instrument to whatever key they like.

Complete code:

const int speakerPin = 10; 
int baseFrequency = 523;
int scale[8] = {523, 587, 659, 698, 784, 880, 988, 1047}; // C5 Major scale

void setup() {
  pinMode(9, INPUT);
  pinMode(8, INPUT);
  pinMode(7, INPUT);
  pinMode(6, INPUT);
  pinMode(5, INPUT);
  pinMode(4, INPUT);
  pinMode(3, INPUT);
  pinMode(2, INPUT);
  pinMode(speakerPin, OUTPUT);

void loop() {
  if (digitalRead(9) == HIGH) {
    tone(speakerPin, scale[0]);
  } else if (digitalRead(8) == HIGH) {
    tone(speakerPin, scale[1]);
  } else if (digitalRead(7) == HIGH) {
    tone(speakerPin, scale[2]);
  } else if (digitalRead(6) == HIGH) {
    tone(speakerPin, scale[3]);
  } else if (digitalRead(5) == HIGH) {
    tone(speakerPin, scale[4]);
  } else if (digitalRead(4) == HIGH) {
    tone(speakerPin, scale[5]);
  } else if (digitalRead(3) == HIGH) {
    tone(speakerPin, scale[6]);
  } else if (digitalRead(2) == HIGH) {
    tone(speakerPin, scale[7]);
  else {
A demonstration of playing the C5 major scale using the Arduino and speaker.