Offline Classroom Controller

#include <Arduino.h>
#include <Wire.h>
#include <U8g2lib.h>
extern "C" {
#include <qrcode.h>
}

const uint8_t NAV_PIN = 2;
const uint8_t SELECT_PIN = 3;
const uint8_t BACK_PIN = 4;
const uint8_t SESSION_PIN = 5;
const uint8_t GREEN_LED_PIN = 6;
const uint8_t YELLOW_LED_PIN = 7;
const uint8_t RED_LED_PIN = 8;
const uint8_t BUZZER_PIN = 9;
const uint8_t NODE_TX_PIN = 10;

U8G2_SSD1327_MIDAS_128X128_1_HW_I2C display(U8G2_R0, U8X8_PIN_NONE);

enum ScreenState { IDLE, CREATE_SESSION, CONFIGURE, GENERATE_QR, READY, ACTIVE, END_SESSION };
ScreenState state = IDLE;

struct Button { uint8_t pin; bool stable; bool lastReading; unsigned long changedAt; };
Button navButton = {NAV_PIN, HIGH, HIGH, 0};
Button selectButton = {SELECT_PIN, HIGH, HIGH, 0};
Button backButton = {BACK_PIN, HIGH, HIGH, 0};
Button sessionButton = {SESSION_PIN, HIGH, HIGH, 0};

uint8_t configItem = 0;
uint8_t roomNumber = 1;
uint8_t attendance = 0;
unsigned long activeStartedAt = 0;
unsigned long lastFaceFrameAt = 0;
uint8_t faceFrame = 0;
bool needsRedraw = true;

bool pressed(Button &button) {
  bool reading = digitalRead(button.pin);
  if (reading != button.lastReading) button.changedAt = millis();
  button.lastReading = reading;
  if ((millis() - button.changedAt) > 25 && reading != button.stable) {
    button.stable = reading;
    return button.stable == LOW;
  }
  return false;
}

void beep(uint16_t durationMs) { digitalWrite(BUZZER_PIN, HIGH); delay(durationMs); digitalWrite(BUZZER_PIN, LOW); }

void sendNodeByte(uint8_t value) {
  const uint16_t bitTime = 104;
  digitalWrite(NODE_TX_PIN, LOW); delayMicroseconds(bitTime);
  for (uint8_t bit = 0; bit < 8; bit++) { digitalWrite(NODE_TX_PIN, (value >> bit) & 1); delayMicroseconds(bitTime); }
  digitalWrite(NODE_TX_PIN, HIGH); delayMicroseconds(bitTime);
}

void sendNodeStatus() {
  const char *message = "IDLE\n";
  if (state == READY) message = "READY,SNTCH-4821\n";
  else if (state == ACTIVE) message = "ACTIVE,SNTCH-4821\n";
  else if (state == END_SESSION) message = "ENDED,SNTCH-4821\n";
  while (*message) sendNodeByte(*message++);
}

void setState(ScreenState next) {
  state = next;
  if (state == ACTIVE) activeStartedAt = millis();
  needsRedraw = true;
  sendNodeStatus();
}

void updateIndicators() {
  digitalWrite(GREEN_LED_PIN, state == READY || state == ACTIVE);
  digitalWrite(YELLOW_LED_PIN, state == CREATE_SESSION || state == CONFIGURE || state == GENERATE_QR);
  digitalWrite(RED_LED_PIN, state == END_SESSION);
}

void drawHeader(const char *title) {
  display.setFont(u8g2_font_5x8_tf);
  display.drawStr(5, 9, title);
  display.drawHLine(4, 12, 120);
}

void drawFace() {
  display.drawFrame(6, 6, 116, 116);
  display.setFont(u8g2_font_5x8_tf);
  display.drawStr(13, 21, "SNTCH  OFFLINE");
  int8_t look = (faceFrame == 3) ? -2 : (faceFrame == 4 ? 2 : 0);
  bool blink = (faceFrame == 1);
  if (blink) { display.drawHLine(38, 58, 10); display.drawHLine(80, 58, 10); }
  else if (faceFrame == 2) { display.drawCircle(43 + look, 58, 5); display.drawCircle(85 + look, 58, 5); }
  else { display.drawDisc(43 + look, 58, 4); display.drawDisc(85 + look, 58, 4); }
  display.drawLine(53, 83, 64, 85); display.drawLine(64, 85, 75, 82);
  display.setFont(u8g2_font_5x8_tf);
  display.drawStr(18, 108, "Press SESSION to begin");
}

void drawConfig() {
  drawHeader("CONFIGURE SESSION");
  display.setFont(u8g2_font_6x10_tf);
  char room[18]; snprintf(room, sizeof(room), "Room: %u", roomNumber);
  display.drawStr(18, 43, room); display.drawStr(18, 65, "Mode: Offline");
  display.setFont(u8g2_font_5x8_tf);
  display.drawStr(18, 90, "Nav: move  Select: change");
  display.drawFrame(10, configItem == 0 ? 30 : 52, 104, 18);
}

void drawQr() {
  drawHeader("JOIN THIS SESSION");
  QRCode qr;
  uint8_t qrData[64];
  qrcode_initText(&qr, qrData, 1, ECC_LOW, "SNTCH:4821");
  const uint8_t scale = 4, x0 = 22, y0 = 18;
  for (uint8_t y = 0; y < qr.size; y++) for (uint8_t x = 0; x < qr.size; x++)
    if (qrcode_getModule(&qr, x, y)) display.drawBox(x0 + x * scale, y0 + y * scale, scale, scale);
  display.setFont(u8g2_font_5x8_tf);
  display.drawStr(20, 112, "ID: SNTCH-4821  CODE: 4821");
}

void drawReady() {
  drawHeader("READY TO START");
  display.setFont(u8g2_font_6x10_tf);
  display.drawStr(24, 43, "Session ready"); display.drawStr(29, 63, "SNTCH-4821");
  display.drawStr(22, 90, "Press SESSION"); display.drawStr(32, 104, "to start");
}

void drawActive() {
  drawHeader("ACTIVE SESSION");
  unsigned long seconds = (millis() - activeStartedAt) / 1000UL;
  char timer[12], count[18];
  snprintf(timer, sizeof(timer), "%02lu:%02lu", seconds / 60UL, seconds % 60UL);
  snprintf(count, sizeof(count), "Present: %u", attendance);
  display.setFont(u8g2_font_logisoso24_tf); display.drawStr(24, 55, timer);
  display.setFont(u8g2_font_6x10_tf); display.drawStr(31, 82, count);
  display.setFont(u8g2_font_5x8_tf); display.drawStr(15, 108, "Select: +1   Session: end");
}

void drawEnd() {
  drawHeader("SESSION ENDED");
  char count[20]; snprintf(count, sizeof(count), "%u attendees saved", attendance);
  display.setFont(u8g2_font_6x10_tf);
  display.drawStr(30, 48, "All done."); display.drawStr(22, 72, count);
  display.setFont(u8g2_font_5x8_tf); display.drawStr(19, 106, "Back: home   Session: new");
}

void drawScreen() {
  display.firstPage();
  do {
    display.setDrawColor(0); display.drawBox(0, 0, 128, 128); display.setDrawColor(1);
    switch (state) {
      case IDLE: drawFace(); break;
      case CREATE_SESSION: drawHeader("CREATE SESSION"); display.setFont(u8g2_font_6x10_tf); display.drawStr(20, 53, "New local session"); display.drawStr(22, 86, "Press SESSION"); break;
      case CONFIGURE: drawConfig(); break;
      case GENERATE_QR: drawQr(); break;
      case READY: drawReady(); break;
      case ACTIVE: drawActive(); break;
      case END_SESSION: drawEnd(); break;
    }
  } while (display.nextPage());
}

void handleControls() {
  if (pressed(navButton)) { if (state == CONFIGURE) { configItem = (configItem + 1) % 2; needsRedraw = true; } beep(18); }
  if (pressed(selectButton)) {
    if (state == CONFIGURE && configItem == 0) { roomNumber = roomNumber % 9 + 1; needsRedraw = true; }
    else if (state == ACTIVE && attendance < 99) { attendance++; needsRedraw = true; }
    beep(25);
  }
  if (pressed(backButton)) {
    if (state == CREATE_SESSION) setState(IDLE); else if (state == CONFIGURE) setState(CREATE_SESSION);
    else if (state == GENERATE_QR) setState(CONFIGURE); else if (state == READY) setState(GENERATE_QR);
    else if (state == END_SESSION) setState(IDLE); beep(20);
  }
  if (pressed(sessionButton)) {
    if (state == IDLE || state == END_SESSION) { attendance = 0; setState(CREATE_SESSION); }
    else if (state == CREATE_SESSION) setState(CONFIGURE); else if (state == CONFIGURE) setState(GENERATE_QR);
    else if (state == GENERATE_QR) setState(READY); else if (state == READY) setState(ACTIVE);
    else if (state == ACTIVE) setState(END_SESSION); beep(55);
  }
}

void setup() {
  pinMode(NAV_PIN, INPUT_PULLUP); pinMode(SELECT_PIN, INPUT_PULLUP); pinMode(BACK_PIN, INPUT_PULLUP); pinMode(SESSION_PIN, INPUT_PULLUP);
  pinMode(GREEN_LED_PIN, OUTPUT); pinMode(YELLOW_LED_PIN, OUTPUT); pinMode(RED_LED_PIN, OUTPUT); pinMode(BUZZER_PIN, OUTPUT);
  pinMode(NODE_TX_PIN, OUTPUT); digitalWrite(NODE_TX_PIN, HIGH);
  Wire.begin(); display.begin(); updateIndicators(); drawScreen();
}

void loop() {
  handleControls(); updateIndicators();
  if (state == IDLE && millis() - lastFaceFrameAt >= 800) { lastFaceFrameAt = millis(); faceFrame = (faceFrame + 1) % 12; needsRedraw = true; }
  if (state == ACTIVE && millis() % 1000 < 25) needsRedraw = true;
  if (needsRedraw) { drawScreen(); needsRedraw = false; }
}