Mini sumo robot for college robo-fests (Arduino Uno + HC-SR04)

// Mini sumo robot — Arduino Uno + 2× TCRT5000 (edge) + HC-SR04 (opponent) + L298N + buzzer module
// Edge sensors face down at the front corners: left DO → D2, right DO → D3.
// HC-SR04 faces forward: Trig D7, Echo D8. Buzzer module I/O → D4.
// L298N: ENA D5, IN1 A0, IN2 A1 (left), ENB D6, IN3 A2, IN4 A3 (right).
// Switch on → five beeps (the 5-second start delay sumo rules ask for) → search, charge, and
// back off whenever a front corner sees the white edge of the black ring (dohyo).
constexpr uint8_t EDGE_L = 2, EDGE_R = 3, TRIG = 7, ECHO = 8, BUZZER = 4;
constexpr uint8_t ENA = 5, IN1 = A0, IN2 = A1;  // left motor
constexpr uint8_t ENB = 6, IN3 = A2, IN4 = A3;  // right motor
// Most TCRT5000 modules pull DO LOW over white and HIGH over black. Flip if yours is opposite.
constexpr bool WHITE_IS_LOW = true;
constexpr uint8_t ATTACK_CM = 40;    // a mini-sumo ring is 77 cm across: anything nearer is the opponent
constexpr uint8_t FULL = 255, SEARCH = 140, BACK = 200;

void motor(uint8_t en, uint8_t a, uint8_t b, int speed) {
  digitalWrite(a, speed >= 0 ? HIGH : LOW);
  digitalWrite(b, speed >= 0 ? LOW : HIGH);
  analogWrite(en, abs(speed));
}

void drive(int left, int right) {
  motor(ENA, IN1, IN2, left);
  motor(ENB, IN3, IN4, right);
}

bool onEdge(uint8_t pin) { return (digitalRead(pin) == LOW) == WHITE_IS_LOW; }

// Distance in cm, or 0 when nothing echoes back within ~1 m.
unsigned int distanceCm() {
  digitalWrite(TRIG, LOW);
  delayMicroseconds(2);
  digitalWrite(TRIG, HIGH);
  delayMicroseconds(10);
  digitalWrite(TRIG, LOW);
  unsigned long us = pulseIn(ECHO, HIGH, 6000UL);  // 6 ms ≈ 1 m: don't wait for far echoes
  return us / 58;
}

void setup() {
  Serial.begin(115200);
  const uint8_t outs[] = {ENA, IN1, IN2, ENB, IN3, IN4, TRIG, BUZZER};
  for (uint8_t p : outs) pinMode(p, OUTPUT);
  pinMode(EDGE_L, INPUT);
  pinMode(EDGE_R, INPUT);
  pinMode(ECHO, INPUT);
  drive(0, 0);
  Serial.println(F("Mini sumo: starting in 5 s"));
  for (uint8_t i = 5; i > 0; i--) {  // 5 s start delay: one beep a second
    Serial.println(i);
    digitalWrite(BUZZER, HIGH);
    delay(i == 1 ? 600 : 150);
    digitalWrite(BUZZER, LOW);
    delay(i == 1 ? 400 : 850);
  }
  Serial.println(F("FIGHT"));
}

void loop() {
  bool left = onEdge(EDGE_L), right = onEdge(EDGE_R);
  if (left || right) {
    // White edge under a front corner: reverse, then turn away from that side.
    Serial.println(left && right ? F("edge: both") : left ? F("edge: left") : F("edge: right"));
    drive(-BACK, -BACK);
    delay(250);
    if (left) drive(SEARCH, -SEARCH);   // edge on the left → turn right
    else drive(-SEARCH, SEARCH);
    delay(220);
    return;
  }
  unsigned int cm = distanceCm();
  if (cm > 0 && cm <= ATTACK_CM) {
    drive(FULL, FULL);  // charge
    Serial.print(F("target "));
    Serial.print(cm);
    Serial.println(F(" cm"));
  } else {
    drive(SEARCH, -SEARCH / 2);  // sweep slowly to the right until the sonar finds it
  }
  delay(15);
}

// Mini sumo robot — Arduino Uno + 2× TCRT5000 (edge) + HC-SR04 (opponent) + L298N + buzzer module
// Edge sensors face down at the front corners: left DO → D2, right DO → D3.
// HC-SR04 faces forward: Trig D7, Echo D8. Buzzer module I/O → D4.
// L298N: ENA D5, IN1 A0, IN2 A1 (left), ENB D6, IN3 A2, IN4 A3 (right).
// Switch on → five beeps (the 5-second start delay sumo rules ask for) → search, charge, and
// back off whenever a front corner sees the white edge of the black ring (dohyo).
constexpr uint8_t EDGE_L = 2, EDGE_R = 3, TRIG = 7, ECHO = 8, BUZZER = 4;
constexpr uint8_t ENA = 5, IN1 = A0, IN2 = A1;  // left motor
constexpr uint8_t ENB = 6, IN3 = A2, IN4 = A3;  // right motor
// Most TCRT5000 modules pull DO LOW over white and HIGH over black. Flip if yours is opposite.
constexpr bool WHITE_IS_LOW = true;
constexpr uint8_t ATTACK_CM = 40;    // a mini-sumo ring is 77 cm across: anything nearer is the opponent
constexpr uint8_t FULL = 255, SEARCH = 140, BACK = 200;

void motor(uint8_t en, uint8_t a, uint8_t b, int speed) {
  digitalWrite(a, speed >= 0 ? HIGH : LOW);
  digitalWrite(b, speed >= 0 ? LOW : HIGH);
  analogWrite(en, abs(speed));
}

void drive(int left, int right) {
  motor(ENA, IN1, IN2, left);
  motor(ENB, IN3, IN4, right);
}

bool onEdge(uint8_t pin) { return (digitalRead(pin) == LOW) == WHITE_IS_LOW; }

// Distance in cm, or 0 when nothing echoes back within ~1 m.
unsigned int distanceCm() {
  digitalWrite(TRIG, LOW);
  delayMicroseconds(2);
  digitalWrite(TRIG, HIGH);
  delayMicroseconds(10);
  digitalWrite(TRIG, LOW);
  unsigned long us = pulseIn(ECHO, HIGH, 6000UL);  // 6 ms ≈ 1 m: don't wait for far echoes
  return us / 58;
}

void setup() {
  Serial.begin(115200);
  const uint8_t outs[] = {ENA, IN1, IN2, ENB, IN3, IN4, TRIG, BUZZER};
  for (uint8_t p : outs) pinMode(p, OUTPUT);
  pinMode(EDGE_L, INPUT);
  pinMode(EDGE_R, INPUT);
  pinMode(ECHO, INPUT);
  drive(0, 0);
  Serial.println(F("Mini sumo: starting in 5 s"));
  for (uint8_t i = 5; i > 0; i--) {  // 5 s start delay: one beep a second
    Serial.println(i);
    digitalWrite(BUZZER, HIGH);
    delay(i == 1 ? 600 : 150);
    digitalWrite(BUZZER, LOW);
    delay(i == 1 ? 400 : 850);
  }
  Serial.println(F("FIGHT"));
}

void loop() {
  bool left = onEdge(EDGE_L), right = onEdge(EDGE_R);
  if (left || right) {
    // White edge under a front corner: reverse, then turn away from that side.
    Serial.println(left && right ? F("edge: both") : left ? F("edge: left") : F("edge: right"));
    drive(-BACK, -BACK);
    delay(250);
    if (left) drive(SEARCH, -SEARCH);   // edge on the left → turn right
    else drive(-SEARCH, SEARCH);
    delay(220);
    return;
  }
  unsigned int cm = distanceCm();
  if (cm > 0 && cm <= ATTACK_CM) {
    drive(FULL, FULL);  // charge
    Serial.print(F("target "));
    Serial.print(cm);
    Serial.println(F(" cm"));
  } else {
    drive(SEARCH, -SEARCH / 2);  // sweep slowly to the right until the sonar finds it
  }
  delay(15);
}