Rotary-encoder music dial

A tiny musical instrument. Turn the knob of the rotary encoder and the passive buzzer plays the next note up or down the scale. Press the knob and it plays a short tune that starts from the note you picked. Along the way you learn how rotary encoders work, the knobs used in car radios and 3D printers.

What you need

• UNO R3 board and USB cable
• Rotary encoder module (45-in-1 Sensor Kit)
• Passive buzzer module (45-in-1 Sensor Kit)
• Breadboard and jumper wires (not included in the Sensor Kit: use the ones from the UNO R3 Starter Kit or any others)

Wiring

Pin labels differ between module versions. Always follow the labels printed on your module.

Use the passive buzzer module here: it can play different notes. The active buzzer can only beep at one pitch.

Build it step by step

1. Wire the encoder and the passive buzzer module as in the diagram.
2. Upload the code and open the Serial Monitor at 9600 baud.
3. Turn the knob slowly. Each click plays the next note and shows its name.
4. Press the knob to play a tune starting from the selected note.

The code

const int CLK_PIN = 2;
const int DT_PIN = 3;
const int SW_PIN = 4;
const int BUZZER_PIN = 8;

// One octave of the C major scale (frequencies in Hz)
const int NOTES[8] = {262, 294, 330, 349, 392, 440, 494, 523};
const char* NAMES[8] = {"C", "D", "E", "F", "G", "A", "B", "high C"};

int note = 0;
int lastClk;

void setup() {
  Serial.begin(9600);
  pinMode(CLK_PIN, INPUT);       // the module has its own pull-up resistors
  pinMode(DT_PIN, INPUT);
  pinMode(SW_PIN, INPUT_PULLUP); // pressed = LOW
  lastClk = digitalRead(CLK_PIN);
  Serial.println("Turn the knob to pick a note, press it to play");
}

void playTune() {
  // Climb up the scale from the chosen note, then back down
  for (int i = note; i < 8; i++) { tone(BUZZER_PIN, NOTES[i], 180); delay(220); }
  for (int i = 7; i >= note; i--) { tone(BUZZER_PIN, NOTES[i], 180); delay(220); }
  noTone(BUZZER_PIN);
}

void loop() {
  int clk = digitalRead(CLK_PIN);
  if (clk != lastClk && clk == LOW) {        // one click of the knob
    if (digitalRead(DT_PIN) != clk) note++;  // clockwise
    else note--;                             // anticlockwise
    note = constrain(note, 0, 7);
    tone(BUZZER_PIN, NOTES[note], 150);
    Serial.println(NAMES[note]);
  }
  lastClk = clk;

  if (digitalRead(SW_PIN) == LOW) {
    playTune();
    while (digitalRead(SW_PIN) == LOW) delay(10);  // wait until released
  }
}

How it works

Inside a rotary encoder, two switches (CLK and DT) open and close as you turn the knob, slightly out of step with each other. When CLK changes, the sketch checks DT: if it's different from CLK the knob turned clockwise, if it's the same it turned anticlockwise. tone() makes the passive buzzer vibrate at a chosen frequency: 262 times per second sounds like the note C, 440 like A.

Make it your own

• Add a second octave and let the knob go higher.
• Program your own melody into playTune().
• Use the encoder to set the brightness of the RGB LED module instead.

Troubleshooting

• Notes skip or go the wrong way: swap the CLK and DT wires, or turn the knob more slowly.
• The buzzer only clicks: you may have the active buzzer. Use the passive one.
• Pressing does nothing: check the SW wire on pin 4.

Learn the basics first

New to these parts? These lessons explain them step by step: Make a tilt alarm with a buzzer and Set up the Arduino IDE and blink an LED.