ESP32 Line Follower: a car that follows a black line on its own

/*
 * TinyBot Forge — ESP32 Line Follower (two IR sensors)
 * https://tinybotforge.com/en/
 *
 * Hardware: ESP32 DevKit V1, 2x TCRT5000 IR line sensor modules, L298N, two TT motors
 * Track: 1.5-2 cm black electrical tape on a white floor
 * Toolchain: Arduino IDE 2.x + ESP32 board package 3.x
 *
 * Most TCRT5000 modules output HIGH on DO over the black line and LOW over white.
 * If yours is the other way round, set LINE_IS_HIGH to false.
 */

const int PIN_SENSOR_L = 34;   // GPIO34/35 are input-only: perfect for sensors
const int PIN_SENSOR_R = 35;
const bool LINE_IS_HIGH = true;

const int PIN_ENA = 25, PIN_IN1 = 26, PIN_IN2 = 27;
const int PIN_ENB = 33, PIN_IN3 = 32, PIN_IN4 = 13;
const int PWM_FREQ = 1000, PWM_BITS = 8;

const int SPEED_STRAIGHT = 150;
const int SPEED_FAST = 170;      // outer wheel while correcting
const int SPEED_SLOW = -60;      // inner wheel while correcting (slightly reversed for a sharper turn)
const unsigned long LOST_MS = 1500;  // stop if the line is lost for this long

int lastTurn = 0;  // -1 = last corrected left, 1 = right
unsigned long lostSince = 0;

void setMotor(int pinEn, int pinA, int pinB, int speed) {
  speed = constrain(speed, -255, 255);
  digitalWrite(pinA, speed > 0 ? HIGH : LOW);
  digitalWrite(pinB, speed < 0 ? HIGH : LOW);
  ledcWrite(pinEn, abs(speed));
}

void drive(int left, int right) {
  setMotor(PIN_ENA, PIN_IN1, PIN_IN2, left);
  setMotor(PIN_ENB, PIN_IN3, PIN_IN4, right);
}

bool onLine(int pin) {
  return digitalRead(pin) == (LINE_IS_HIGH ? HIGH : LOW);
}

void setup() {
  Serial.begin(115200);
  pinMode(PIN_SENSOR_L, INPUT);
  pinMode(PIN_SENSOR_R, INPUT);
  pinMode(PIN_IN1, OUTPUT); pinMode(PIN_IN2, OUTPUT);
  pinMode(PIN_IN3, OUTPUT); pinMode(PIN_IN4, OUTPUT);
  ledcAttach(PIN_ENA, PWM_FREQ, PWM_BITS);
  ledcAttach(PIN_ENB, PWM_FREQ, PWM_BITS);
  drive(0, 0);
  delay(2000);
}

void loop() {
  bool l = onLine(PIN_SENSOR_L);
  bool r = onLine(PIN_SENSOR_R);

  if (!l && !r) {
    // line is between the sensors: go straight
    drive(SPEED_STRAIGHT, SPEED_STRAIGHT);
    lostSince = 0;
  } else if (l && !r) {
    // left sensor on the line: car drifted right, steer left
    drive(SPEED_SLOW, SPEED_FAST);
    lastTurn = -1;
    lostSince = 0;
  } else if (!l && r) {
    // right sensor on the line: steer right
    drive(SPEED_FAST, SPEED_SLOW);
    lastTurn = 1;
    lostSince = 0;
  } else {
    // both on black: a crossing or overshoot; search in the last direction
    if (lostSince == 0) lostSince = millis();
    if (millis() - lostSince > LOST_MS) {
      drive(0, 0);
    } else if (lastTurn < 0) {
      drive(SPEED_SLOW, SPEED_FAST);
    } else {
      drive(SPEED_FAST, SPEED_SLOW);
    }
  }
  delay(5);
}