Using a line follower and a touch sensor, we turned a basic Arduino robot into an autonomous navigator. The robot was coded to follow specific tracks and dodge obstacles based on logic. This challenge was a great way to see how software programming directly controls physical machines.

// ============================================================

// VERSION 2: auto-calibrating line follower + obstacle avoidance

// Based on SparkFun's official "Getting Started with the RedBot"

// tutorial: uses setBGLevel()/setDetectLevel() so the sensors

// calibrate THEMSELVES - no more manual threshold guessing.

//

// Line sensors: A3 (left), A6 (center), A7 (right)

// Whisker bumpers: pin 3 (left), pin 11 (right)

//   (official tutorial uses pin 10 for left - change below if

//    your left whisker never registers)

// Onboard D12 button = calibrate/start. D13 LED = status.

//

// ---------------- HOW TO USE (calibration ritual) ----------------

// 1. Power on. LED BLINKS SLOWLY.

//    -> Hold the robot so ALL THREE sensors are over BARE FLOOR.

//    -> Press the onboard D12 button.  (LED flashes fast = floor saved)

// 2. LED BLINKS FAST.

//    -> Turn the robot sideways so the tape line runs LEFT-TO-RIGHT

//       underneath ALL THREE sensors at once.

//    -> Press the D12 button again.   (LED goes solid = tape saved)

// 3. LED SOLID = ready. Put the robot on the track (line under the

//    center sensor, robot pointing along the line). It starts after

//    2 seconds.

// ------------------------------------------------------------------

#include <RedBot.h>

RedBotMotors motors;

RedBotSensor left   = RedBotSensor(A3);

RedBotSensor center = RedBotSensor(A6);

RedBotSensor right  = RedBotSensor(A7);

RedBotBumper leftBumper  = RedBotBumper(3);   // tutorial uses 10; try it

RedBotBumper rightBumper = RedBotBumper(11);  //   if 3 never triggers

#define BUTTON_PIN 12

#define LED_PIN    13

const int SPEED   = 100;  // cruising speed (below ~75 may not have

                          // enough torque to start moving)

const int TRIM    = 7;    // left-motor correction for drift

const int TURN_90 = 400;  // ms of pivot for ~90 degrees

void driveStraight(int speed) {

  motors.leftMotor(-(speed - TRIM));

  motors.rightMotor(speed);

}

// LED blink helper

void blinkLED(int times, int ms) {

  for (int i = 0; i < times; i++) {

    digitalWrite(LED_PIN, HIGH); delay(ms);

    digitalWrite(LED_PIN, LOW);  delay(ms);

  }

}

void setup() {

  Serial.begin(9600);

  pinMode(BUTTON_PIN, INPUT_PULLUP);

  pinMode(LED_PIN, OUTPUT);

  // ---- STEP 1: calibrate the FLOOR (background) ----

  // Slow blink while waiting: put all three sensors over bare floor,

  // then press the button.

  while (digitalRead(BUTTON_PIN) == HIGH) {

    digitalWrite(LED_PIN, HIGH); delay(400);

    digitalWrite(LED_PIN, LOW);  delay(400);

  }

  left.setBGLevel();      // sensors memorize what "floor" looks like

  center.setBGLevel();

  right.setBGLevel();

  blinkLED(6, 60);        // fast flash = floor saved

  delay(300);

  // ---- STEP 2: calibrate the TAPE (line) ----

  // Fast blink while waiting: lay the tape line sideways under all

  // three sensors, then press the button.

  while (digitalRead(BUTTON_PIN) == HIGH) {

    digitalWrite(LED_PIN, HIGH); delay(120);

    digitalWrite(LED_PIN, LOW);  delay(120);

  }

  left.setDetectLevel();  // sensors memorize what "tape" looks like

  center.setDetectLevel();

  right.setDetectLevel();

  digitalWrite(LED_PIN, HIGH);  // solid = calibrated and ready

  delay(2000);                  // time to place it on the track

}

void loop() {

  // check() = true when a sensor sees the tape (per its own calibration)

  bool lOn = left.check();

  bool cOn = center.check();

  bool rOn = right.check();

  // Debug (Serial Monitor, 9600 baud)

  Serial.print("L:");  Serial.print(left.read());

  Serial.print(lOn ? "*" : " ");

  Serial.print(" C:"); Serial.print(center.read());

  Serial.print(cOn ? "*" : " ");

  Serial.print(" R:"); Serial.print(right.read());

  Serial.print(rOn ? "*" : " ");

  Serial.print(" LB:"); Serial.print(leftBumper.read());

  Serial.print(" RB:"); Serial.println(rightBumper.read());

  // --- 1. Obstacle check (whisker pressed = LOW) ---

  bool hitL = (leftBumper.read()  == LOW);

  bool hitR = (rightBumper.read() == LOW);

  if (hitL && hitR) {

    motors.brake();                // head-on: stop hard, back up, 180

    delay(300);

    driveStraight(-SPEED);

    delay(700);

    motors.pivot(SPEED);

    delay(TURN_90 * 2);

    driveStraight(SPEED);

    delay(800);

    return;

  }

  else if (hitL || hitR) {

    driveStraight(-SPEED);         // back away

    delay(700);

    if (hitL) motors.pivot(SPEED);   // left hit -> 90 right

    else      motors.pivot(-SPEED);  // right hit -> 90 left

    delay(TURN_90);

    driveStraight(SPEED);          // drive off in the new direction

    delay(800);

    return;

  }

  // --- 2. Line following: move ONLY when a sensor sees the tape ---

  if (cOn) {

    driveStraight(SPEED);          // tape under center -> straight

  }

  else if (lOn) {

    motors.pivot(-SPEED);          // tape drifted left -> turn left

  }

  else if (rOn) {

    motors.pivot(SPEED);           // tape drifted right -> turn right

  }

  else {

    motors.brake();                // no tape anywhere -> hard stop

  }

}