Beginner Guide: Make a Bluetooth + Obstacle Avoidance Robot Car (4 Motors)

#include <SoftwareSerial.h>
#include <NewPing.h>

// ———- Bluetooth ———-
SoftwareSerial BT(2, 3);                               // D2 = RX, D3 = TX

// ———- Ultrasonic ———-
#define TRIG_PIN 12
#define ECHO_PIN 13
#define MAX_DISTANCE 200
NewPing sonar(TRIG_PIN, ECHO_PIN, MAX_DISTANCE);

// ———- Motor Driver ———-
#define ENA 5                             // Left Motor Speed (PWM)
#define IN1 7                            // Left Motor Direction
#define IN2 8
#define ENB 6                           // Right Motor Speed (PWM)
#define IN3 9 // Right Motor Direction
#define IN4 10

// ———- Variables ———-
bool autoMode = false;
int baseSpeed = 180; // Default speed (0–255)

// ———- Motor Functions ———-
void setLeft(int spd, bool forward) {
analogWrite(ENA, spd);
digitalWrite(IN1, forward ? HIGH : LOW);
digitalWrite(IN2, forward ? LOW : HIGH);
}

void setRight(int spd, bool forward) {
analogWrite(ENB, spd);
digitalWrite(IN3, forward ? HIGH : LOW);
digitalWrite(IN4, forward ? LOW : HIGH);
}

void stopAll() {
analogWrite(ENA, 0);
analogWrite(ENB, 0);
digitalWrite(IN1, LOW);
digitalWrite(IN2, LOW);
digitalWrite(IN3, LOW);
digitalWrite(IN4, LOW);
}

void forward() {
setLeft(baseSpeed, true);
setRight(baseSpeed, true);
}

void backward() {
setLeft(baseSpeed, false);
setRight(baseSpeed, false);
}

void leftTurn() {
setLeft(baseSpeed, false);
setRight(baseSpeed, true);
}

void rightTurn() {
setLeft(baseSpeed, true);
setRight(baseSpeed, false);
}

// ———- Ultrasonic Distance ———-
int getDist() {
int d = sonar.ping_cm();
return (d == 0) ? MAX_DISTANCE : d;              // return MAX if no object
}

// ———- Setup ———-
void setup() {
pinMode(ENA, OUTPUT);
pinMode(IN1, OUTPUT);
pinMode(IN2, OUTPUT);
pinMode(ENB, OUTPUT);
pinMode(IN3, OUTPUT);
pinMode(IN4, OUTPUT);

stopAll(); // Ensure motors are off at start

Serial.begin(9600);
BT.begin(9600);

Serial.println(“Robot Ready!”);
}

// ———- Loop ———-
void loop() {
// ———- Bluetooth Commands ———-
if (BT.available()) {
char c = BT.read();

if (c >= ‘0‘ && c <= ‘9‘) {
// Speed control 0–9 maps to 80–255
baseSpeed = map(c – ‘0‘, 0, 9, 80, 255);
Serial.print(“Speed set to: “);
Serial.println(baseSpeed);
} else {
switch (c) {
case ‘F‘: autoMode = false; forward(); Serial.println(“Forward“); break;
case ‘B‘: autoMode = false; backward(); Serial.println(“Backward“); break;
case ‘L‘: autoMode = false; leftTurn(); Serial.println(“Left“); break;
case ‘R‘: autoMode = false; rightTurn(); Serial.println(“Right“); break;
case ‘S‘: autoMode = false; stopAll(); Serial.println(“Stop“); break;
case ‘A‘: autoMode = true; Serial.println(“Auto Mode ON“); break;
case ‘M‘: autoMode = false; stopAll(); Serial.println(“Manual Mode“); break;
}
}
}

// ———- Auto Mode ———-
if (autoMode) {
int d = getDist();
Serial.print(“Distance: “);
Serial.println(d);

if (d < 20) {
stopAll(); delay(100);

backward(); delay(300);
stopAll(); delay(100);

rightTurn(); delay(400);
stopAll(); delay(100);
} else {
forward();
}
}
}