Obstacle Avoidance Robot

Arduino-powered autonomous robot with servo-scanning ultrasonic detection and intelligent path selection. Built from scratch during a college robotics internship.

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📖 Overview

Most basic obstacle-avoidance robots stop and blindly turn in one fixed direction. This robot does it smarter.

An HC-SR04 ultrasonic sensor is mounted on an SG90 servo motor that sweeps left and right. When an obstacle is detected, the robot stops, actively scans both sides, measures free space, and turns toward the clearer path. This makes navigation noticeably smoother and less prone to getting cornered.

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✨ What Makes This Different

Feature	Basic Obstacle Bot	This Robot
Detection	Fixed forward only	Servo scans left + right
Turn decision	Always same direction	Picks side with more space
Sensor library	NewPing (abstracted)	Raw pulseIn() — full control
Code structure	Single loop blob	Modular functions per behavior

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🧰 Hardware

Component	Model	Purpose
Microcontroller	Arduino UNO / Nano	Main brain
Ultrasonic Sensor	HC-SR04	Distance measurement
Servo Motor	SG90 9g	Rotates sensor left/right
Motor Driver	L298N or L293D Shield	Controls motor speed & direction
Drive Motors	BO DC Gear Motors (×2)	Differential drive
Caster Wheel	Front ball caster	Balance & smooth turning
Chassis	2WD Robot Car Kit	Physical frame
Power	9V Battery or 7.4V LiPo	Main supply
Switch	SPST toggle	ON/OFF control
Hardware	Nuts, bolts, spacers	Mechanical assembly

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🔊 How the Sensor Works

The HC-SR04 works by timing a sound pulse:

1. Arduino sends a 10µs HIGH pulse to TRIG pin
2. Sensor fires 8 ultrasonic bursts at 40kHz
3. Sound wave travels forward, hits object, bounces back
4. ECHO pin goes HIGH for the duration of the round-trip
5. Arduino reads pulse duration via pulseIn()
6. Distance (cm) = duration × 0.034 / 2

Speed of sound ≈ 343 m/s = 0.034 cm/µs. Divide by 2 because the pulse travels to the obstacle and back.

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🧠 Decision Logic

[Read distance straight ahead]
        │
  dist < 20cm?
   /         \
  NO          YES
  │            │
[Move Forward]  [Stop Motors]
  │            │
(repeat)  [Servo → 150°] ← look LEFT
          [Read leftDist]
               │
          [Servo → 30°]  ← look RIGHT
          [Read rightDist]
               │
          [Servo → 90°]  ← re-center
               │
      leftDist > rightDist?
        /              \
      YES               NO
       │                 │
  [Turn Left]       [Turn Right]
        \               /
         └──[Move Forward]──► (repeat)

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💻 Core Code (Arduino C++)

#include <Servo.h>

#define TRIG_PIN  9
#define ECHO_PIN  10
#define SERVO_PIN 11
#define SAFE_DIST 20    // cm

Servo scanServo;

long getDistance() {
  digitalWrite(TRIG_PIN, LOW);
  delayMicroseconds(2);
  digitalWrite(TRIG_PIN, HIGH);
  delayMicroseconds(10);
  digitalWrite(TRIG_PIN, LOW);
  long duration = pulseIn(ECHO_PIN, HIGH, 30000);
  return (duration == 0) ? 999 : duration * 0.034 / 2;
}

long scanAt(int angle) {
  scanServo.write(angle);
  delay(350);
  return getDistance();
}

void loop() {
  long dist = getDistance();
  if (dist > SAFE_DIST) {
    moveForward();
  } else {
    stopMotors();
    long leftDist  = scanAt(150);
    long rightDist = scanAt(30);
    scanAt(90);
    leftDist > rightDist ? turnLeft(450) : turnRight(450);
  }
}

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🔌 Wiring

HC-SR04 → Arduino

Sensor Pin	Arduino Pin	Notes
VCC	5V	Do NOT use 3.3V
GND	GND	Common ground
TRIG	D9	Output from Arduino
ECHO	D10	Input to Arduino

SG90 Servo → Arduino

Servo Wire	Arduino Pin	Notes
Signal (Orange)	D11	PWM pin required
VCC (Red)	5V	Share with sensor
GND (Brown)	GND	Common ground

L298N Motor Driver → Arduino

Driver Pin	Arduino Pin / Source
IN1	D4
IN2	D5
IN3	D6
IN4	D7
ENA	D3 (PWM)
ENB	D8
Vin	9V Battery (+)
GND	Battery (–) + Arduino GND

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🚀 Getting Started

1. Clone the repo: git clone https://github.com/YOUR_USERNAME/obstacle-avoidance-robot.git
2. Open src/obstacle_avoidance/obstacle_avoidance.ino in Arduino IDE
3. Select Board → Arduino UNO and correct COM Port
4. Click Upload ✓
5. Disconnect USB, insert 9V battery, flip switch — done!

No external libraries needed. Servo.h is built into Arduino IDE.

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🌍 Real-World Applications

• 🚗 Self-driving cars — radar/lidar-based obstacle detection and path planning
• 🏭 Warehouse robots — Amazon Kiva robots navigating around shelves and people
• 🏠 Home cleaning robots — Roomba's bump-and-scan navigation
• 🛸 Mars rovers — Perseverance uses stereo cameras for autonomous hazard detection
• ♿ Smart wheelchairs — obstacle detection to assist mobility

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📊 Hardware Component Map

🛠️ Future Improvements

• IR sensors for cliff / edge detection
• PID-controlled turning for smoother arcs
• Bluetooth module for live sensor data on phone
• OLED display showing distance readings in real time
• Upgrade to ROS2-based navigation stack
• Battery voltage monitor with LED indicator

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👤 Author

Moosa Mubasir

Collaborative college robotics project — learning embedded systems, sensor integration, and autonomous logic from the ground up.

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📄 License

MIT License — free to use, fork, and build on.