Quiz buzzer system for 4 teams with lockout (Arduino Uno + TM1637 + WS2812B)

// Quiz buzzer system — Arduino Uno + 4 team buttons + host button + TM1637 + WS2812B stick + buzzer.
// The host presses OPEN to start a question. The first team to press wins: the display shows
// "P  2", that team's two LEDs light in its colour and the buzzer sounds. Later presses are
// listed in order on the Serial Monitor. A team holding its button when the question opens is
// locked out for that question (no early pressing).
// Team buttons D2–D5 (to GND), OPEN button D6 (to GND), TM1637 CLK D7 / DIO D8,
// WS2812B DIN D9 through 330 Ω, active buzzer module I/O D10.
#include <TM1637Display.h>
#include <Adafruit_NeoPixel.h>

constexpr uint8_t HOST_PIN = 6;
constexpr uint8_t CLK = 7, DIO = 8;
constexpr uint8_t LED_PIN = 9;
constexpr uint8_t NUM_LEDS = 8;  // two per team
constexpr uint8_t BUZZER_PIN = 10;

TM1637Display display(CLK, DIO);
Adafruit_NeoPixel strip(NUM_LEDS, LED_PIN, NEO_GRB + NEO_KHZ800);

// Team colours: red, green, blue, yellow (0xRRGGBB, as Adafruit_NeoPixel::Color packs them).
const uint32_t TEAM_COLOR[4] = {0xFF0000, 0x00FF00, 0x0000FF, 0xFFB000};
const uint8_t READY[] = {SEG_E | SEG_G, SEG_A | SEG_D | SEG_E | SEG_F | SEG_G, SEG_B | SEG_C | SEG_D | SEG_E | SEG_G,
                         SEG_B | SEG_C | SEG_D | SEG_F | SEG_G};  // "rEdy"
const uint8_t SEG_P = SEG_A | SEG_B | SEG_E | SEG_F | SEG_G;

enum State : uint8_t { IDLE, ARMED, LOCKED };
State state = IDLE;
unsigned long armedAt = 0, firstMs = 0, buzzOffAt = 0, lastShown = 0;
uint8_t lockedOut = 0;  // bit n = team n+1 was holding its button when the question opened
uint8_t answered = 0;   // bit n = team n+1 has pressed during this question
uint8_t place = 0;
bool hostWasDown = false;

// All four team buttons are on port D (PD2–PD5), so one read of PIND samples them at the
// same instant — no team is favoured by the order the pins are checked in.
uint8_t teamsDown() { return (~PIND >> 2) & 0x0F; }

void beep(unsigned int ms) {
  digitalWrite(BUZZER_PIN, HIGH);
  buzzOffAt = millis() + ms;
}

void lightTeam(uint8_t team, uint32_t color) {
  strip.setPixelColor(team * 2, color);
  strip.setPixelColor(team * 2 + 1, color);
}

void allLeds(uint32_t color) {
  strip.fill(color);
  strip.show();
}

void openQuestion() {
  state = ARMED;
  answered = 0;
  place = 0;
  lockedOut = teamsDown();
  armedAt = millis();
  lastShown = 0xFFFF;
  allLeds(0x101010);  // dim white: question open
  beep(60);
  Serial.println(F("\nQuestion open — buzzers live"));
  for (uint8_t t = 0; t < 4; t++)
    if (lockedOut & (1 << t)) {
      Serial.print(F("Team "));
      Serial.print(t + 1);
      Serial.println(F(" was already pressing — locked out for this question"));
    }
}

void recordPress(uint8_t team, unsigned long ms) {
  answered |= 1 << team;
  place++;
  Serial.print(place);
  Serial.print(F(". Team "));
  Serial.print(team + 1);
  if (place == 1) {
    firstMs = ms;
    Serial.print(F(" first, "));
    Serial.print((ms - armedAt) / 1000.0, 2);
    Serial.println(F(" s after the question opened"));
    state = LOCKED;
    const uint8_t segs[] = {SEG_P, 0, 0, display.encodeDigit(team + 1)};
    display.setSegments(segs);
    strip.clear();
    lightTeam(team, TEAM_COLOR[team]);
    strip.show();
    beep(400);
  } else {
    Serial.print(F(" — "));
    Serial.print((ms - firstMs) / 1000.0, 3);
    Serial.println(F(" s behind"));
  }
}

void setup() {
  for (uint8_t pin = 2; pin <= 5; pin++) pinMode(pin, INPUT_PULLUP);
  pinMode(HOST_PIN, INPUT_PULLUP);
  pinMode(BUZZER_PIN, OUTPUT);
  Serial.begin(115200);
  display.setBrightness(7);
  strip.begin();
  strip.setBrightness(80);  // 8 LEDs at this level stay well inside USB power
  // Colour check at power-up: each team's pair lights in turn.
  for (uint8_t t = 0; t < 4; t++) {
    lightTeam(t, TEAM_COLOR[t]);
    strip.show();
    delay(200);
  }
  display.setSegments(READY);
  allLeds(0x101010);
  Serial.println(F("Quiz buzzer ready. Press OPEN (D6) to start a question."));
  Serial.println(F("Before the show: hold any team button now to test it — its LEDs light up."));
}

void loop() {
  unsigned long now = millis();
  if (buzzOffAt && (long)(now - buzzOffAt) >= 0) {
    digitalWrite(BUZZER_PIN, LOW);
    buzzOffAt = 0;
  }

  // Host button: open the next question on each press (falling edge, debounced).
  bool hostDown = digitalRead(HOST_PIN) == LOW;
  if (hostDown && !hostWasDown) {
    openQuestion();
    delay(30);
  }
  hostWasDown = hostDown;

  uint8_t down = teamsDown();
  if (state == IDLE) {
    // Button test between rounds: a held button lights its team's LEDs.
    static uint8_t lastDown = 0xFF;
    if (down != lastDown) {
      for (uint8_t t = 0; t < 4; t++) lightTeam(t, (down & (1 << t)) ? TEAM_COLOR[t] : 0x101010);
      strip.show();
      lastDown = down;
    }
    return;
  }

  // Locked-out teams count again once they let go and press afresh in the next question only.
  uint8_t fresh = down & ~lockedOut & ~answered & 0x0F;
  if (fresh) {
    // A tie inside one PIND read (a few microseconds) goes to the lower team number.
    for (uint8_t t = 0; t < 4; t++)
      if (fresh & (1 << t)) recordPress(t, now);
  }

  if (state == ARMED) {
    // Elapsed seconds since the question opened: "-  7".
    unsigned int s = (now - armedAt) / 1000;
    if (s != lastShown) {
      lastShown = s;
      const uint8_t dash[] = {SEG_G};
      display.setSegments(dash, 1, 0);
      display.showNumberDec(min(s, 999u), false, 3, 1);
    }
  }
}

// Quiz buzzer system — Arduino Uno + 4 team buttons + host button + TM1637 + WS2812B stick + buzzer.
// The host presses OPEN to start a question. The first team to press wins: the display shows
// "P  2", that team's two LEDs light in its colour and the buzzer sounds. Later presses are
// listed in order on the Serial Monitor. A team holding its button when the question opens is
// locked out for that question (no early pressing).
// Team buttons D2–D5 (to GND), OPEN button D6 (to GND), TM1637 CLK D7 / DIO D8,
// WS2812B DIN D9 through 330 Ω, active buzzer module I/O D10.
#include <TM1637Display.h>
#include <Adafruit_NeoPixel.h>

constexpr uint8_t HOST_PIN = 6;
constexpr uint8_t CLK = 7, DIO = 8;
constexpr uint8_t LED_PIN = 9;
constexpr uint8_t NUM_LEDS = 8;  // two per team
constexpr uint8_t BUZZER_PIN = 10;

TM1637Display display(CLK, DIO);
Adafruit_NeoPixel strip(NUM_LEDS, LED_PIN, NEO_GRB + NEO_KHZ800);

// Team colours: red, green, blue, yellow (0xRRGGBB, as Adafruit_NeoPixel::Color packs them).
const uint32_t TEAM_COLOR[4] = {0xFF0000, 0x00FF00, 0x0000FF, 0xFFB000};
const uint8_t READY[] = {SEG_E | SEG_G, SEG_A | SEG_D | SEG_E | SEG_F | SEG_G, SEG_B | SEG_C | SEG_D | SEG_E | SEG_G,
                         SEG_B | SEG_C | SEG_D | SEG_F | SEG_G};  // "rEdy"
const uint8_t SEG_P = SEG_A | SEG_B | SEG_E | SEG_F | SEG_G;

enum State : uint8_t { IDLE, ARMED, LOCKED };
State state = IDLE;
unsigned long armedAt = 0, firstMs = 0, buzzOffAt = 0, lastShown = 0;
uint8_t lockedOut = 0;  // bit n = team n+1 was holding its button when the question opened
uint8_t answered = 0;   // bit n = team n+1 has pressed during this question
uint8_t place = 0;
bool hostWasDown = false;

// All four team buttons are on port D (PD2–PD5), so one read of PIND samples them at the
// same instant — no team is favoured by the order the pins are checked in.
uint8_t teamsDown() { return (~PIND >> 2) & 0x0F; }

void beep(unsigned int ms) {
  digitalWrite(BUZZER_PIN, HIGH);
  buzzOffAt = millis() + ms;
}

void lightTeam(uint8_t team, uint32_t color) {
  strip.setPixelColor(team * 2, color);
  strip.setPixelColor(team * 2 + 1, color);
}

void allLeds(uint32_t color) {
  strip.fill(color);
  strip.show();
}

void openQuestion() {
  state = ARMED;
  answered = 0;
  place = 0;
  lockedOut = teamsDown();
  armedAt = millis();
  lastShown = 0xFFFF;
  allLeds(0x101010);  // dim white: question open
  beep(60);
  Serial.println(F("\nQuestion open — buzzers live"));
  for (uint8_t t = 0; t < 4; t++)
    if (lockedOut & (1 << t)) {
      Serial.print(F("Team "));
      Serial.print(t + 1);
      Serial.println(F(" was already pressing — locked out for this question"));
    }
}

void recordPress(uint8_t team, unsigned long ms) {
  answered |= 1 << team;
  place++;
  Serial.print(place);
  Serial.print(F(". Team "));
  Serial.print(team + 1);
  if (place == 1) {
    firstMs = ms;
    Serial.print(F(" first, "));
    Serial.print((ms - armedAt) / 1000.0, 2);
    Serial.println(F(" s after the question opened"));
    state = LOCKED;
    const uint8_t segs[] = {SEG_P, 0, 0, display.encodeDigit(team + 1)};
    display.setSegments(segs);
    strip.clear();
    lightTeam(team, TEAM_COLOR[team]);
    strip.show();
    beep(400);
  } else {
    Serial.print(F(" — "));
    Serial.print((ms - firstMs) / 1000.0, 3);
    Serial.println(F(" s behind"));
  }
}

void setup() {
  for (uint8_t pin = 2; pin <= 5; pin++) pinMode(pin, INPUT_PULLUP);
  pinMode(HOST_PIN, INPUT_PULLUP);
  pinMode(BUZZER_PIN, OUTPUT);
  Serial.begin(115200);
  display.setBrightness(7);
  strip.begin();
  strip.setBrightness(80);  // 8 LEDs at this level stay well inside USB power
  // Colour check at power-up: each team's pair lights in turn.
  for (uint8_t t = 0; t < 4; t++) {
    lightTeam(t, TEAM_COLOR[t]);
    strip.show();
    delay(200);
  }
  display.setSegments(READY);
  allLeds(0x101010);
  Serial.println(F("Quiz buzzer ready. Press OPEN (D6) to start a question."));
  Serial.println(F("Before the show: hold any team button now to test it — its LEDs light up."));
}

void loop() {
  unsigned long now = millis();
  if (buzzOffAt && (long)(now - buzzOffAt) >= 0) {
    digitalWrite(BUZZER_PIN, LOW);
    buzzOffAt = 0;
  }

  // Host button: open the next question on each press (falling edge, debounced).
  bool hostDown = digitalRead(HOST_PIN) == LOW;
  if (hostDown && !hostWasDown) {
    openQuestion();
    delay(30);
  }
  hostWasDown = hostDown;

  uint8_t down = teamsDown();
  if (state == IDLE) {
    // Button test between rounds: a held button lights its team's LEDs.
    static uint8_t lastDown = 0xFF;
    if (down != lastDown) {
      for (uint8_t t = 0; t < 4; t++) lightTeam(t, (down & (1 << t)) ? TEAM_COLOR[t] : 0x101010);
      strip.show();
      lastDown = down;
    }
    return;
  }

  // Locked-out teams count again once they let go and press afresh in the next question only.
  uint8_t fresh = down & ~lockedOut & ~answered & 0x0F;
  if (fresh) {
    // A tie inside one PIND read (a few microseconds) goes to the lower team number.
    for (uint8_t t = 0; t < 4; t++)
      if (fresh & (1 << t)) recordPress(t, now);
  }

  if (state == ARMED) {
    // Elapsed seconds since the question opened: "-  7".
    unsigned int s = (now - armedAt) / 1000;
    if (s != lastShown) {
      lastShown = s;
      const uint8_t dash[] = {SEG_G};
      display.setSegments(dash, 1, 0);
      display.showNumberDec(min(s, 999u), false, 3, 1);
    }
  }
}