Obstacle Avoiding Car

An autonomous robot that uses ultrasonic sensing for real-time obstacle detection and collision avoidance. Built with Arduino UNO R4 WiFi and L298N motor driver.

Overview

The Obstacle Avoiding Car is an autonomous robotic vehicle that navigates its environment by detecting obstacles using an HC-SR04 ultrasonic sensor. The system continuously measures distance to objects ahead and stops movement when obstacles are detected within a 60cm threshold, preventing collisions. The robot resumes forward motion when the path is clear.

This implementation uses the Arduino UNO R4 WiFi (Renesas RA4M1 microcontroller) for control logic, an L298N H-bridge motor driver for dual DC motor control, and ultrasonic ranging for distance measurement.

Project Background

This project was developed to explore fundamental concepts in autonomous robotics, including:

Sensor Integration: Working with ultrasonic time-of-flight sensors for distance measurement
Motor Control: Implementing H-bridge driver circuits for bidirectional DC motor control
Real-time Decision Making: Creating responsive control algorithms for obstacle avoidance
Embedded Systems: Programming microcontrollers for real-world hardware interaction

Technical Challenges Addressed:

Reliable distance measurement with ultrasonic sensors (handling timeouts and echo detection)
Motor driver interfacing and control signal management
Real-time loop timing and sensor polling optimization
Serial debugging for system state monitoring

Features

Autonomous Navigation: Self-directed forward movement with automatic obstacle detection
Ultrasonic Distance Sensing: HC-SR04 sensor with 60cm detection threshold
Dual Motor Control: Independent left/right motor control via L298N driver
Real-time Serial Output: Distance measurements logged to serial monitor at 9600 baud
Collision Prevention: Automatic motor stop when obstacles detected
Simple Control Logic: Straightforward decision tree for easy modification and learning

Hardware Requirements

Bill of Materials (BOM)

Component	Specifications	Quantity
Arduino UNO R4 WiFi	Renesas RA4M1 (Cortex-M4), 5V logic, USB-C	1
L298N Motor Driver Module	Dual H-bridge, 5-35V, 2A per channel	1
DC Motors	3-12V DC geared motors (TT motors recommended)	2
HC-SR04 Ultrasonic Sensor	5V, 2-400cm range, 40kHz	1
Jumper Wires	Male-to-male and male-to-female	~15
Power Supply	7.4V LiPo or 6x AA batteries (9V), 2A minimum	1
Robot Chassis	2WD or 4WD platform with motor mounts	1
Switch	Power on/off switch (optional)	1

Power Supply Notes:

Motors require external power (cannot run from Arduino 5V rail)
Recommended: 7.4V 2S LiPo battery or 6x AA battery pack
L298N requires minimum 7V for stable 5V logic output

Pin Configuration

Complete Pin Mapping Table

Component	Pin Type	Arduino Pin	L298N/Sensor Pin	Function
Right Motor Forward	Digital Output	D4	IN1	Drive right motor forward
Right Motor Backward	Digital Output	D3	IN2	Drive right motor backward
Left Motor Forward	Digital Output	D2	IN3	Drive left motor forward
Left Motor Backward	Digital Output	D5	IN4	Drive left motor backward
Ultrasonic Trigger	Digital Output	D12	HC-SR04 Trig	Send 10μs trigger pulse
Ultrasonic Echo	Digital Input	D13	HC-SR04 Echo	Receive echo pulse (max 20ms)

Pin Definitions in Code:

#define BACKWARDR 3   // Right motor backward
#define FORWARDR 4    // Right motor forward
#define BACKWARDL 5   // Left motor backward
#define FORWARDL 2    // Left motor forward
#define TRIGGER_PIN 12
#define ECHO_PIN 13

Wiring Diagram

L298N Motor Driver to Arduino

L298N Pin	Arduino Pin	Description
IN1	D4	Right motor control 1
IN2	D3	Right motor control 2
IN3	D2	Left motor control 1
IN4	D5	Left motor control 2
GND	GND	Common ground
+5V	—	Not connected (L298N provides 5V out)

L298N Motor Driver to Motors

L298N Pin	Connection	Description
OUT1	Right Motor +	Right motor positive
OUT2	Right Motor −	Right motor negative
OUT3	Left Motor +	Left motor positive
OUT4	Left Motor −	Left motor negative

Motor Polarity Note: If a motor runs backwards, swap its + and − connections.

L298N Power Connections

L298N Pin	Connection	Description
+12V	Battery +	External power supply (7-12V)
GND	Battery −	External power ground
+5V OUT	—	Can power Arduino 5V pin (jumper must be installed)

Important: Remove the L298N 5V regulator jumper if using >12V to prevent damage.

HC-SR04 Ultrasonic Sensor to Arduino

HC-SR04 Pin	Arduino Pin	Description
VCC	5V	Power supply
Trig	D12	Trigger input
Echo	D13	Echo output
GND	GND	Ground

Power Distribution

Battery (+) ──→ L298N (+12V)
Battery (−) ──→ L298N (GND) ──→ Arduino (GND)
Arduino (5V) ──→ HC-SR04 (VCC)

Grounding: Ensure Arduino GND and L298N GND share a common ground connection.

Safety Warnings

⚠️ IMPORTANT: Read Before Operation

Voltage Limits: Do not exceed 12V input to L298N. Higher voltages may damage the regulator.
Current Rating: Motors should not exceed 2A per channel. Use appropriate motor selection.
Heat Dissipation: L298N heatsink may become hot during operation. Avoid direct contact.
Polarity: Verify battery polarity before connection. Reverse polarity can damage components.
Short Circuits: Check all connections for shorts before applying power.
Testing Environment: Test in a safe, open area away from stairs, ledges, or fragile objects.
Power Switch: Install a power switch for emergency shutoff.
Motor Stall: Prolonged motor stall (blocked wheels) can overheat the L298N.

Software Requirements

Development Environment

Arduino IDE: Version 2.0 or later recommended (Download)
Board Package: Arduino Renesas UNO R4 Boards
- Install via: Tools → Board → Boards Manager → Search "Renesas"
USB Driver: Automatic with Arduino IDE installation

Libraries

No external libraries required. This project uses only standard Arduino libraries:

Built-in digital I/O functions
Built-in serial communication
Built-in timing functions (pulseIn, delay, delayMicroseconds)

Installation & Setup

Step-by-Step Setup Guide

1. Repository Setup

git clone https://github.com/Legion345/obstacle-avoiding-car.git
cd obstacle-avoiding-car

2. Hardware Assembly

Mount motors to chassis
Attach wheels to motor shafts
Secure Arduino and L298N to chassis
Mount HC-SR04 sensor at front of chassis (facing forward, unobstructed)

3. Wiring Verification

Double-check all connections against the Wiring Diagram
Verify motor polarity (test with external power source if uncertain)
Confirm ultrasonic sensor orientation (sensor face should be forward)
Ensure common ground between Arduino and L298N

4. Software Installation

Install Arduino IDE 2.x
Open Arduino IDE
Navigate to: Tools → Board → Boards Manager
Search for "Renesas" and install Arduino Renesas UNO R4 Boards

5. Code Upload

Open obstacle_avoiding_car.ino in Arduino IDE
Select board: Tools → Board → Arduino UNO R4 Boards → Arduino UNO R4 WiFi
Select port: Tools → Port → [Your COM/tty port]
Click Upload button (or Ctrl+U)

6. Testing & Calibration

Open Serial Monitor: Tools → Serial Monitor
Set baud rate to 9600
Power on the robot (external battery connected to L298N)
Observe distance readings in Serial Monitor
Place an object 60cm away and verify robot stops
Test movement by clearing the path

7. Calibration (if needed)

If distance readings seem inaccurate, verify:
- Sensor is firmly mounted
- No vibration during operation
- Speed of sound constant is correct for your environment (default: 343 m/s at 20°C)

Code Architecture

The code consists of four main components:

1. setup() - Initialization

Configures motor control pins (D2-D5) as outputs
Configures ultrasonic sensor pins (D12 trigger, D13 echo)
Initializes serial communication at 9600 baud

2. loop() - Main Control Logic

Checks distance: if < 60cm, stops motors; otherwise moves forward
Triggers ultrasonic sensor with 10μs pulse
Measures echo pulse duration using pulseIn() with 20ms timeout
Calculates distance: distance = duration × 0.0343 / 2
Logs distance to serial monitor

3. moveForward() - Motor Control

Activates both motors by setting forward pins HIGH

4. Distance Calculation

Uses speed of sound (343 m/s or 0.0343 cm/μs at 20°C)
Divides by 2 to account for sound's round-trip travel

Algorithm Flow

Control Flow Diagram

START
  ↓
[Initialize pins and serial]
  ↓
  ├─→ [Check: distanceCm < 60?]
  │     ├─ YES → [Stop motors (set forward pins LOW)]
  │     │         └─→ [delay(200)]
  │     │
  │     └─ NO → [moveForward() - activate both motors]
  │               └─→ [delay(500)]
  ↓
[Send ultrasonic trigger pulse]
  ├─ Set TRIGGER_PIN LOW (2μs)
  ├─ Set TRIGGER_PIN HIGH (10μs)
  └─ Set TRIGGER_PIN LOW
  ↓
[Measure echo pulse duration]
  └─ duration = pulseIn(ECHO_PIN, HIGH, 20000)
  ↓
[Calculate distance]
  └─ distanceCm = duration × 0.0343 / 2
  ↓
[Log to serial monitor]
  └─ Serial.print("Distance: X cm")
  ↓
[Loop back to decision logic]
  └─→ [Continue loop]

Timing Analysis

Loop Cycle Breakdown:

Decision + Motor control: ~200-500ms (delay dependent on path status)
Ultrasonic trigger: ~12μs
Echo measurement: Variable (0-20ms, depends on distance)
Distance calculation: <1μs
Serial output: ~1ms

Total loop time: Approximately 200-520ms per iteration

Effective measurement rate: ~2-5 Hz (adequate for slow-moving robot)

Acknowledgments

Resources and References

[List any tutorials or resources used during development]

Helpful Resources:

HC-SR04 Datasheet
L298N Motor Driver Datasheet
Arduino UNO R4 WiFi Documentation
Arduino Community Forums for troubleshooting support

Libraries Used:

Arduino Core Library (included with Arduino IDE)

License

This project is licensed under the MIT License.

MIT License

Copyright (c) 2026 Legion345

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.

Author

Legion345

GitHub: @Legion345
Project Repository: obstacle-avoiding-car

For questions, suggestions, or collaboration opportunities, feel free to open an issue or reach out via GitHub.

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README.md		README.md
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Obstacle Avoiding Car

Table of Contents

Overview

Project Background

Features

Hardware Requirements

Bill of Materials (BOM)

Pin Configuration

Complete Pin Mapping Table

Wiring Diagram

L298N Motor Driver to Arduino

L298N Motor Driver to Motors

L298N Power Connections

HC-SR04 Ultrasonic Sensor to Arduino

Power Distribution

Safety Warnings

Software Requirements

Development Environment

Libraries

Installation & Setup

Step-by-Step Setup Guide

Code Architecture

Algorithm Flow

Control Flow Diagram

Timing Analysis

Acknowledgments

Resources and References

License

Author

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