DIY Arduino Smart 4wd Obstacle Avoider with Dynamic Speed Control

1. INTRODUCTION

In modern robotics, smooth movement is just as important as logic. Most basic obstacle-avoiding robots move at a fixed, jerky speed. This project upgrades the classic design by using Pulse Width Modulation (PWM). Our robot will now act intelligently: sprinting when the path is clear and slowing down cautiously as it approaches an object.

2. COMPONENTS

Microcontroller: Arduino Uno R3
Motor Driver: L298N Dual H-Bridge Module
Chassis: 4WD Robot Car Kit (4 DC Motors)
Sensor: HC-SR04 Ultrasonic Sensor
Actuator: SG90 Servo Motor
Power: 12V Li-ion Battery Pack
Jumpers: Male-to-Male and Male-to-Female wires

3. CIRCUIT AND CONNECTIONS

Power Distribution Connections

From (Source)	To (Destination)	Purpose
Battery (+) 12V	L298N 12V Terminal	Main Power
Battery (+) 12V	Arduino VIN Pin	Power Arduino
Battery (–) GND	L298N GND Terminal	Common Ground
L298N GND	Arduino GND Pin	Common Ground
Arduino 5V	Ultrasonic & Servo VCC	Logic Power

L298N Connections

L298N Terminal	Arduino Pin	Function
ENA	Pin 10 (PWM)	Left Motors Speed
IN1	Pin 9	Left Motors Forward
IN2	Pin 8	Left Motors Backward
IN3	Pin 7	Right Motors Forward
IN4	Pin 4	Right Motors Backward
ENB	Pin 5 (PWM)	Right Motors Speed

L298N SIDE TERMINAL	MOTOR WIRES (PAIRING)
OUT1 & OUT2	Connect both Left Front and Left Rear motor wires here.
OUT3 & OUT4	Connect both Right Front and Right Rear motor wires here.

Ultrasonic Sensor Pin Connections

HC SR 04 Terminal	Arduino Pin
Trigger pin	Pin 11
Echo pin	Pin 12
VCC	To 5V
GND	To GND

Servo Motor Pin Connections

Sero Motor Terminal	Arduino Pin
VCC	To 5V VCC
GND	To GND
Control	Pin 3

4. CIRCUIT WORKING

The L298N acts as the brain's "muscle," allowing the Arduino to drive high-current motors. By connecting ENA and ENB to PWM pins (10 and 5), we can vary the voltage. The HC-SR04 sends sound waves; the time they take to return tells the Arduino the distance. The Servo allows the sensor to "scan" 180 degrees to find the best path when forward movement is blocked.

5. CODE

#include <Servo.h>

int enA = 10; int in1 = 9; int in2 = 8;
int enB = 5;  int in3 = 7; int in4 = 4;
int trig = 11; int echo = 12;
Servo myServo;

void setup() {
  pinMode(enA, OUTPUT); pinMode(enB, OUTPUT);
  pinMode(in1, OUTPUT); pinMode(in2, OUTPUT);
  pinMode(in3, OUTPUT); pinMode(in4, OUTPUT);
  myServo.attach(3);
  myServo.write(90);
}

void loop() {
  int distance = getDistance();
  if (distance > 50 || distance == 0) {
    moveForward(255); // Full Speed
  } else if (distance <= 50 && distance > 20) {
    moveForward(150); // Slowing Down
  } else {
    stopRobot();
    scanAndTurn();
  }
}

int getDistance() {
  digitalWrite(trig, LOW); delayMicroseconds(2);
  digitalWrite(trig, HIGH); delayMicroseconds(10);
  digitalWrite(trig, LOW);
  return pulseIn(echo, HIGH) * 0.034 / 2;
}

void moveForward(int s) {
  digitalWrite(in1, HIGH); digitalWrite(in2, LOW);
  digitalWrite(in3, HIGH); digitalWrite(in4, LOW);
  analogWrite(enA, s); analogWrite(enB, s);
}

void stopRobot() {
  analogWrite(enA, 0); analogWrite(enB, 0);
  delay(200);
}

void scanAndTurn() {
  myServo.write(20); delay(500);
  int dRight = getDistance();
  myServo.write(160); delay(500);
  int dLeft = getDistance();
  myServo.write(90);
  if (dLeft > dRight) {
    digitalWrite(in1, LOW); digitalWrite(in2, HIGH);
    digitalWrite(in3, HIGH); digitalWrite(in4, LOW);
  } else {
    digitalWrite(in1, HIGH); digitalWrite(in2, LOW);
    digitalWrite(in3, LOW); digitalWrite(in4, HIGH);
  }
  analogWrite(enA, 200); analogWrite(enB, 200);
  delay(500);
}

6. CODE WORKING

The code uses a conditional if-else structure. It constantly checks the getDistance() function. If the distance is large, analogWrite(255) is sent to the Enable pins. As the distance drops below 50cm, it switches to analogWrite(150). If an object is too close (< 20cm), the robot stops, triggers the scanAndTurn() function to compare left vs. right distances, and chooses the clearer path.

7. TIPS

Common Ground: Ensure the Battery GND and Arduino GND are connected.
Power Supply: Use a 12V source for 4WD chassis; 9V batteries often drain too fast.
PWM Pins: Only pins with the ~ symbol (3, 5, 6, 9, 10, 11) support speed control.

8. USES

Warehouse Automation: Small-scale version of AGVs (Automated Guided Vehicles).
Exploration: Educational base for rovers in unknown environments.
Service Robots: Foundations for vacuum or delivery robots.

9. CONCLUSION

By implementing dynamic speed, we have transformed a simple hobby project into a sophisticated robotic platform. This setup reduces motor wear and makes the robot's navigation appear much more natural and "human-like."

Basic Electronics for Beginners

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