This week covers:
• Introduction to electronics production and soldering
• Microcontroller programming and interfacing
• MIDI protocol and music controller development
• Display integration and user interface design
• Touch sensing and capacitive input methods

• Understand electronics production and soldering techniques
• Learn microcontroller programming with QPAD development environment
• Develop MIDI controller applications
• Integrate OLED displays for visual feedback
• Implement capacitive touch sensing
• Create interactive music interfaces

Controller Soldering

• Assembled QPAD21 controller in workshop
• Soldered all components including microcontroller, touch sensors, and display
• Tested basic functionality and connectivity

MIDI Controller Development

• Programmed QPAD-based MIDI controller
• Implemented capacitive touch sensing for 6 touch pads
• Created piano keyboard mapping with MIDI note output
• Added OLED display for visual feedback

Display Integration

• Integrated Adafruit SSD1306 OLED display
• Created piano keyboard visualization
• Implemented real-time touch feedback display
• Added note name indicators and touch pad status

Project Overview

This week's assignment focused on electronics production and microcontroller programming. The main project involved soldering a QPAD21 controller in the workshop and then programming it to function as a MIDI piano controller with an integrated OLED display showing a visual piano keyboard interface.

Hardware Components

• Microcontroller: QPAD21 board with capacitive touch capabilities
• Touch Sensors: 6 capacitive touch pads (Q0-Q5) for piano input
• Display: Adafruit SSD1306 OLED 128x64 display for visual feedback
• LED: Status indicator for touch events
• MIDI Output: Serial communication for MIDI note transmission

Software Implementation

The controller runs custom code that combines touch sensing, MIDI output, and display management: Key Features: • Capacitive Touch Sensing: 6 touch pads with configurable threshold
• MIDI Protocol: Standard MIDI Note On/Off messages
• Piano Mapping: Maps touch pads to piano notes (C4, D4, E4, F4, G4, A4)
• Visual Display: Real-time piano keyboard visualization
• Debouncing: 300ms debounce delay to prevent multiple triggers
Technical Specifications: • MIDI Channel: Channel 1
• Touch Threshold: 750 (configurable)
• Display Resolution: 128x64 pixels
• Update Rate: 50ms loop delay
• Serial Communication: 31250 baud for MIDI

QPAD Code

Code written using Cursor IDE and compiled/uploaded with Arduino IDE

/*
 * QPAD21 MIDI Piano Controller
 * 
 * Touch pads play piano notes and display the corresponding keys
 * Simple MIDI output for testing with Hairless MIDI
 * 
 * Developed in Cursor IDE, compiled with Arduino IDE
 */

#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>
#include <Adafruit_FreeTouch.h>

// Display configuration
#define SCREEN_WIDTH 128
#define SCREEN_HEIGHT 64
#define OLED_RESET -1
#define SCREEN_ADDRESS 0x3C
Adafruit_SSD1306 display(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire, OLED_RESET);

// Hardware pins
#define PIN_LED 15
#define N_TOUCH 6
#define THRESHOLD 750

// Touch pad configuration
uint8_t touch_pins[N_TOUCH] = {2, 3, 4, 5, 6, 7};
Adafruit_FreeTouch* touch_devices[N_TOUCH];

// Touch state tracking
int touch_values[N_TOUCH] = {0, 0, 0, 0, 0, 0};
bool pin_touched_now[N_TOUCH] = {false, false, false, false, false, false};
bool pin_touched_past[N_TOUCH] = {false, false, false, false, false, false};

// Debouncing
unsigned long last_touch_time[N_TOUCH] = {0, 0, 0, 0, 0, 0};
#define DEBOUNCE_DELAY 300 // 300ms debounce delay

// Piano notes (MIDI note numbers) - matches Microsoft GS Wavetable Synth
// These are the standard piano notes that sound good on Microsoft GS Wavetable Synth
byte piano_notes[N_TOUCH] = {60, 62, 64, 65, 67, 69}; // C4, D4, E4, F4, G4, A4
String note_names[N_TOUCH] = {"C4", "D4", "E4", "F4", "G4", "A4"};

// MIDI Configuration
#define MIDI_CHANNEL 1

void update_touch() {
  Ptc *ptc = ((Ptc *)PTC);

  for (int i = 0; i < N_TOUCH; i++) {
    touch_devices[i]->begin();
    touch_values[i] = touch_devices[i]->measure();
    
    ptc->CTRLA.bit.ENABLE = 0;
    ptc->CTRLA.bit.SWRESET = 1;
    
    pin_touched_past[i] = pin_touched_now[i];
    pin_touched_now[i] = touch_values[i] > THRESHOLD;
  }
}

void send_midi_note(byte note, byte velocity) {
  // Send MIDI Note On message
  Serial.write(0x90 | (MIDI_CHANNEL - 1)); // Note On, Channel 1
  Serial.write(note);
  Serial.write(velocity);
}

void send_midi_note_off(byte note) {
  // Send MIDI Note Off message
  Serial.write(0x80 | (MIDI_CHANNEL - 1)); // Note Off, Channel 1
  Serial.write(note);
  Serial.write((byte)0); // Velocity 0
}

void handle_touch_events() {
  unsigned long current_time = millis();
  
  for (int i = 0; i < N_TOUCH; i++) {
    // Note On when touched
    if (pin_touched_now[i] && !pin_touched_past[i] && (current_time - last_touch_time[i] > DEBOUNCE_DELAY)) {
      last_touch_time[i] = current_time;
      send_midi_note(piano_notes[i], 127); // Send Note On
      digitalWrite(PIN_LED, HIGH);
    }
    
    // Note Off when released
    if (!pin_touched_now[i] && pin_touched_past[i]) {
      send_midi_note_off(piano_notes[i]); // Send Note Off
      digitalWrite(PIN_LED, LOW);
    }
  }
}

void draw_piano_keyboard() {
  display.clearDisplay();
  
  // Draw title
  display.setTextSize(1);
  display.setCursor(0, 0);
  display.print("QPAD21 Piano");
  
  // Piano keyboard dimensions
  int key_width = 18;
  int key_height = 30;
  int start_x = 5;
  int start_y = 15;
  
  // Draw white keys (6 keys)
  for (int i = 0; i < N_TOUCH; i++) {
    int x = start_x + (i * key_width);
    int y = start_y;
    
    // Draw key background
    if (pin_touched_now[i]) {
      // Key pressed - filled rectangle
      display.fillRect(x, y, key_width - 1, key_height, SSD1306_WHITE);
      // Draw note name in black (inverted)
      display.setTextColor(SSD1306_BLACK);
      display.setCursor(x + 2, y + 8);
      display.print(note_names[i]);
      display.setTextColor(SSD1306_WHITE);
    } else {
      // Key not pressed - outline rectangle
      display.drawRect(x, y, key_width - 1, key_height, SSD1306_WHITE);
      // Draw note name in white
      display.setTextColor(SSD1306_WHITE);
      display.setCursor(x + 2, y + 8);
      display.print(note_names[i]);
    }
  }
  
  // Draw black keys (sharps) - smaller keys on top
  int black_key_width = 12;
  int black_key_height = 20;
  
  // Draw black keys for sharps (C#, D#, F#, G#)
  int black_keys[] = {0, 1, 3, 4}; // Q0, Q1, Q3, Q4 have sharps
  String black_note_names[] = {"C#", "D#", "F#", "G#"};
  
  for (int i = 0; i < 4; i++) {
    int key_index = black_keys[i];
    int x = start_x + (key_index * key_width) + (key_width / 2) - (black_key_width / 2);
    int y = start_y;
    
    // Draw black key
    display.fillRect(x, y, black_key_width, black_key_height, SSD1306_WHITE);
    // Draw note name in black
    display.setTextColor(SSD1306_BLACK);
    display.setCursor(x + 1, y + 5);
    display.print(black_note_names[i]);
    display.setTextColor(SSD1306_WHITE);
  }
  
  // Draw touch pad indicators at bottom
  display.setCursor(0, 50);
  display.print("Q0 Q1 Q2 Q3 Q4 Q5");
  
  // Draw pressed indicators
  display.setCursor(0, 58);
  for (int i = 0; i < N_TOUCH; i++) {
    if (pin_touched_now[i]) {
      display.print(" * ");
    } else {
      display.print(" - ");
    }
  }
  
  display.display();
}

void setup() {
  // Initialize serial for MIDI output
  Serial.begin(31250);
  
  // Initialize touch devices
  for (int i = 0; i < N_TOUCH; i++) {
    touch_devices[i] = new Adafruit_FreeTouch(touch_pins[i], OVERSAMPLE_1, RESISTOR_100K, FREQ_MODE_NONE);
  }
  
  // Initialize LED
  pinMode(PIN_LED, OUTPUT);
  digitalWrite(PIN_LED, LOW);
  
  // Initialize display
  if (!display.begin(SSD1306_SWITCHCAPVCC, SCREEN_ADDRESS)) {
    // Display initialization failed - flash LED
    for (int i = 0; i < 10; i++) {
      digitalWrite(PIN_LED, HIGH);
      delay(100);
      digitalWrite(PIN_LED, LOW);
      delay(100);
    }
  }
  
  // Initial display
  display.clearDisplay();
  display.setTextSize(1);
  display.setTextColor(SSD1306_WHITE);
  display.setCursor(10, 25);
  display.println("QPAD21 Piano");
  display.setCursor(10, 35);
  display.println("Ready!");
  display.display();
  
  delay(1000);
}

void loop() {
  // Update touch sensors
  update_touch();
  
  // Handle touch events
  handle_touch_events();
  
  // Update display
  draw_piano_keyboard();
  
  // Small delay
  delay(50);
}

Completed QPAD21 controller after soldering and assembly


OLED display showing piano keyboard interface with touch feedback


Video demonstration of QPAD21 MIDI Piano Controller in action

This week provided valuable experience in electronics production and microcontroller programming. Soldering the QPAD21 controller board taught me precision and attention to detail in hardware assembly. Programming the MIDI controller combined multiple technical skills including touch sensing, display management, and MIDI protocol implementation. The visual piano keyboard interface makes the controller intuitive to use, and the real-time feedback enhances the user experience.

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