Project 1: Chord Sequencer Pt 2

September 30, 2020

Last update I had begun to build and program a musical arpeggiator/sequencer, and had reached a point where I could start/stop a musical sequence with a button. There was still plenty of work to do to implement my vision. I needed to add LED output that shows which step is playing, and multiple inputs to control tempo, arpeggio speed and which arpeggios are playing. I also needed to eliminate delay from my code so that the tone output would not prevent the sensors from being read in real time.

The first thing I addressed was the delay issue. I incorporated a library called Takser which exposes an API similar to JavaScript’s timer functions. It allows you to set hierarchy of timers and intervals that execute independently. I refactored my loop function to work within this new framework by creating an interval for playing notes that executed every step and an interval to watch for the on/off button press.

Next I wired four LEDs to display which step is being played. I wrote logic to activate each LED when the corresponding step is active. Here is the code at this point:

// #define TASKER_MAX_TASKS 32
#include <Tasker.h>
#include "pitches.h"

Tasker tasker(true);

const int speakerPin = 8;
const int buttonPin = 2;
bool isPlaying = false;

int toggleButtonState;
int prevToggleButtonState;

int bpm = 65;
// duration of a beat in ms
float beatDuration = 60.0 / bpm * 1000;
int noteDuration = beatDuration / 3;
int stepCount = 0;

int LED_STEP_PINS[] = {5, 6, 4, 3};

int CHORDS[4][3] = {
  {NOTE_C3, NOTE_E3, NOTE_G3},
  {NOTE_E3, NOTE_G3, NOTE_B2},
  {NOTE_F3, NOTE_A3, NOTE_C3},
  {NOTE_D3, NOTE_F3, NOTE_A2},
};

void handleButtonPress() {
  toggleButtonState = digitalRead(buttonPin);
  if (toggleButtonState != prevToggleButtonState) {
    if (toggleButtonState == HIGH) {
      Serial.println("toggle on off");
      isPlaying = !isPlaying;
    }
  }
  prevToggleButtonState = toggleButtonState;
}

void playNote(int note) {
  Serial.println("playing note: ");
  Serial.println(note);

  tone(speakerPin, note, noteDuration * 0.9);
}

void playStep() {
  if (isPlaying) {
    for (int i = 0; i < 4; i++) {
      if (i == stepCount) {
        digitalWrite(LED_STEP_PINS[i], HIGH);
      } else {
        digitalWrite(LED_STEP_PINS[i], LOW);
      }
    }

    for (int i = 0; i < 3; i++) {
      int note = CHORDS[stepCount][i];
      tasker.setTimeout(playNote, i * noteDuration + 1, note);
    }

    stepCount++;
    stepCount = stepCount % 4;
  }
}

void setup() {
  Serial.begin(9600);

  pinMode(buttonPin, INPUT);
  pinMode(speakerPin, OUTPUT);
  prevToggleButtonState = digitalRead(buttonPin);

  tasker.setInterval(handleButtonPress, 1);
  tasker.setInterval(playStep, beatDuration);
}

void loop() {
  tasker.loop();
}

The LEDs now showed the sequence.

LEDs in sync with the sequence (note: very low volume)

My next step was to add two buttons, one to cycle through selected steps and the other to the arpeggio at a the selected step. I also wanted to visualize this by making the LED at the selected step blink. After wiring the two buttons I added another interval that would simply blink the active step. I hard-coded an array of the seven three-note chords in the C major scale and created another array to represent which chord index was supposed to play at each of the four steps.

I added logic for the buttons to control the activeStep and chords[] variables which determine which chord to play at each step.

I also needed to change the sequencer structure. Before, each step was creating multiple intervals based on the arpeggio’s divisions, which was causing timing inconsistencies and dropped notes. I solved this by executing the interval every note (instead of every step which could play multiple notes) and determining which step was active by counting notes.

#include <Tasker.h>
#include "chords.h"

Tasker tasker(true);

const int SPEAKER_PIN = 8;
const int BUTTON_PIN = 2;
const int LED_STEP_PINS[] = {5, 6, 4, 3};
const int INCREMENT_STEP_PIN = 9;
const int INCREMENT_CHORD_PIN = 7;

const int TOTAL_CHORDS = 4;

bool isPlaying = false;

int onOffButtonState;
int prevOnOffButtonState;

int incrementStepButtonState;
int prevIncrementStepButtonState;

int incrementChordButtonState;
int prevIncrementChordButtonState;

float beatDuration;
int beatDivisions = 6;

int currentChord = 0;
int currentStep = 0;

int activeStep = 0;

int chords[] = {0, 4, 5, 3};

// ------------------------------------------------------------------

void setBpm(int bpm)
{
  // duration of a beat in ms
  beatDuration = 60.0 / bpm * 1000;
}

void stopSequence()
{
  noTone(SPEAKER_PIN);

  // reset position
  currentStep = 0;
  currentChord = 0;

  // Turn off LEDs
  for (int i = 0; i < TOTAL_CHORDS; i++)
  {
    digitalWrite(LED_STEP_PINS[i], LOW);
  }
}

void playNoteStep()
{
  if (!isPlaying)
  {
    noTone(SPEAKER_PIN);
    return;
  };

  // Turn on LED for current chord step
  for (int i = 0; i < TOTAL_CHORDS; i++)
  {
    if (i == currentChord)
    {
      digitalWrite(LED_STEP_PINS[i], HIGH);
    }
    else
    {
      digitalWrite(LED_STEP_PINS[i], LOW);
    }
  }

  // cycle through notes in the chord
  int currentNoteIndex = currentStep % 3;
  int note = C_MAJ_CHORDS[chords[currentChord]][currentNoteIndex];
  float noteDuration = beatDuration / beatDivisions;
  tone(SPEAKER_PIN, note, noteDuration * 0.8);

  currentStep++;
  currentStep = currentStep % beatDivisions;

  // increment chord when steps cycle
  if (currentStep == 0)
  {
    currentChord++;
    currentChord = currentChord % TOTAL_CHORDS;
  }
}

// ------------------------------------------------------------------

int blinkVal = LOW;
void blinkActiveStep() {
  for (int i = 0; i < TOTAL_CHORDS; i++)
  {
    if (i == activeStep)
    {
      digitalWrite(LED_STEP_PINS[i], blinkVal);
      blinkVal = !blinkVal;
    }
  }
}

// BUTTON HANDLERS ------------------------------------------------------------------

void watchForStartButtonPress()
{
  onOffButtonState = digitalRead(BUTTON_PIN);
  if (onOffButtonState != prevOnOffButtonState)
  {
    if (onOffButtonState == HIGH)
    {
      Serial.println("Toggle on/off");
      isPlaying = !isPlaying;
      if (!isPlaying)
      {
        stopSequence();
      }
    }
  }
  prevOnOffButtonState = onOffButtonState;
}

void watchForIncrementStepPress()
{
  incrementStepButtonState = digitalRead(INCREMENT_STEP_PIN);
  if (incrementStepButtonState != prevIncrementStepButtonState)
  {
    if (incrementStepButtonState == HIGH)
    {
      Serial.println("Select Next Step");
      // Clear current blink
      for (int i = 0; i < TOTAL_CHORDS; i++)
      {
        digitalWrite(LED_STEP_PINS[activeStep], LOW);
      }
      activeStep++;
      activeStep = activeStep % TOTAL_CHORDS;
    }
  }
  prevIncrementStepButtonState = incrementStepButtonState;
}

void watchForIncrementChordPress()
{
  incrementChordButtonState = digitalRead(INCREMENT_CHORD_PIN);
  if (incrementChordButtonState != prevIncrementChordButtonState)
  {
    if (incrementChordButtonState == HIGH)
    {
      Serial.println("Increment Chord");
      int nextChordIndex = chords[activeStep];
      nextChordIndex++;
      nextChordIndex = nextChordIndex % 7;
      chords[activeStep] = nextChordIndex;
    }
  }
  prevIncrementChordButtonState = incrementChordButtonState;
}

// ------------------------------------------------------------------

void setup()
{
  Serial.begin(9600);

  setBpm(70);

  pinMode(BUTTON_PIN, INPUT);
  pinMode(INCREMENT_STEP_PIN, INPUT);
  pinMode(INCREMENT_CHORD_PIN, INPUT);

  pinMode(SPEAKER_PIN, OUTPUT);

  // initialize button states
  prevOnOffButtonState = digitalRead(BUTTON_PIN);
  prevIncrementStepButtonState = digitalRead(INCREMENT_STEP_PIN);
  prevIncrementChordButtonState = digitalRead(INCREMENT_CHORD_PIN);

  tasker.setInterval(watchForStartButtonPress, 1);
  tasker.setInterval(watchForIncrementStepPress, 1);
  tasker.setInterval(watchForIncrementChordPress, 1);
  tasker.setInterval(blinkActiveStep, 100);

  float noteDuration = beatDuration / beatDivisions;
  tasker.setInterval(playNoteStep, noteDuration, 0);
}

void loop()
{
  tasker.loop();
}

With this code running I could cycle through each step and increment it’s chord:

Selecting and changing the chord at different steps (note: very low volume)

Now it was time to add some analog input. I wanted three dials — one to control tempo (how fast the steps progress), one to control arpeggio divisions (how many notes are played per step — does not affect tempo), and one to control note duration (how long each note lasts). I wired three potentiometers to the Arduino (each with a pulldown resistor) and implemented logic to read these values.

The final schematic of my sequencer

You can view the final code on GitHub. When the tempo or step divisions are adjusted, I needed to re-initiate the sequence because its timing is based on those values — this happens in the resetInterval function. I refactored the interval logic so that instead of multiple intervals firing every millisecond to read button presses and potentiometers, there is just one function to read all input.

Here is a short demonstration of the final device! I wish I had been able to create some sort of housing but I had trouble figuring out how since the buttons, LEDs, and potentiometers all have different heights.

The final product! (note: very low volume)