Arduino UNO Bluetooth 4WD Robot Car | MakeMindz Tutorial

⚙️ Robotics ✅ Beginner 📶 Bluetooth

Arduino UNO Bluetooth Controlled 4WD Robot Car

Build a wireless smartphone-controlled robot car using Arduino UNO, HC-05 Bluetooth, and L298N dual H-bridge motor driver — complete with circuit diagram, full code, and simulation link.

⏱ 30–60 min 💰 ~₹600–₹900 🎓 Beginner 📅 Feb 2026

⬇ Get the Code 🔬 Run Simulation

Project Overview

The Arduino UNO Bluetooth Controlled 4WD Robot Car is a beginner-friendly project where a smartphone sends single-character commands via Bluetooth to the Arduino, which drives four DC motors through the L298N H-bridge motor driver — enabling forward, backward, left, right and stop.

ℹ️

How it worksPhone sends F/B/L/R/S → HC-05 passes it to Arduino via UART → Arduino toggles L298N IN1–IN4 pins to spin motors.

✅ What You'll Learn

UART / Serial communication
H-bridge motor direction control
Bluetooth wireless pairing
Multi-motor synchronisation

⚠️ Prerequisites

Arduino IDE installed
Basic wiring knowledge
Android phone (Bluetooth)
USB-A to USB-B cable

Components Needed

🧠

Arduino UNO R3

× 1 — Microcontroller

⚡

L298N Motor Driver

× 1 — Dual H-Bridge

📶

HC-05 Bluetooth

× 1 — Serial BT Module

🔧

DC Geared Motors

× 4 — TT type, 3–6V

🚗

4WD Robot Chassis

× 1 — with wheels

🔋

Battery Pack

× 1 — 6V / 4×AA

💡

LED + 220Ω Resistor

× 1 — Status light

🔌

Jumper Wires

M-F and M-M set

Pin Connections

Arduino Pin	Connects To	Description
D13	L298N IN1	Left channel — Forward
D12	L298N IN2	Left channel — Reverse
D11	L298N IN3	Right channel — Forward
D10	L298N IN4	Right channel — Reverse
D9	LED Anode (via 220Ω)	Status indicator
D0 RX	HC-05 TX	Bluetooth receive
D1 TX	HC-05 RX (via divider)	Bluetooth transmit
5V	HC-05 VCC	Module power
GND	HC-05 GND, L298N GND, Battery −	Common ground

Circuit Diagram

🔌 Wiring Schematic — Arduino 4WD Bluetooth Robot Car SVG

⚠️

Voltage Divider on HC-05 RXThe HC-05 RX pin is 3.3V tolerant. Use a 1kΩ + 2kΩ resistor divider between Arduino TX (5V) and HC-05 RX to protect the module.

Step-by-Step Build Guide

Gather All Components

Collect everything from the components list above. Use a dedicated 6V battery pack for the motors — don't power them from Arduino's 5V pin, as motors draw too much current.

Assemble the 4WD Chassis

Mount all 4 DC geared motors into the chassis slots and secure with screws. Attach rubber wheels. Left motors (FL + BL) share one L298N output channel; right motors (FR + BR) share the other.

💡 If the car veers to one side, swap the two motor wires on the affected channel.

Wire the L298N Motor Driver

IN1 → Arduino D13
IN2 → Arduino D12
IN3 → Arduino D11
IN4 → Arduino D10
OUT-A → Left motors (FL + BL)
OUT-B → Right motors (FR + BR)
VCC → Battery pack positive (+)
GND → Battery (−) and Arduino GND

⚠️ Keep ENA/ENB jumpers ON for full speed, or wire to D5/D6 for PWM speed control.

Connect HC-05 Bluetooth Module

VCC → Arduino 5V
GND → Arduino GND
TX → Arduino RX (D0)
RX → Arduino TX (D1) via 1kΩ/2kΩ voltage divider

💡 Disconnect HC-05 TX/RX before uploading code — it shares the hardware serial port and will block USB upload.

Wire the LED Status Indicator

Connect LED anode (+) through a 220Ω resistor to Arduino D9. Connect cathode (−) to GND. Toggle it via commands 'O' (on) and 'f' (off).

Upload the Arduino Sketch

Open Arduino IDE, paste the code from Section 06
Tools → Board → Arduino UNO
Tools → Port → select your COM port
Disconnect HC-05 TX/RX wires temporarily
Click Upload (→) — wait for "Done uploading"
Reconnect HC-05 wires after upload

Pair & Test with Your Phone

Power on the robot (battery + USB/Vin)
Android: Settings → Bluetooth → Scan
Pair with HC-05 — default PIN: 1234 or 0000
Install Serial Bluetooth Terminal app
Connect to HC-05 and send: F, B, L, R, S

✅ HC-05 LED blinks fast before pairing, then once every 2 seconds when connected.

Arduino Sketch

bluetooth_4wd_robot.ino

/*
 * Arduino UNO Bluetooth Controlled 4WD Robot Car
 * HC-05 Bluetooth + L298N Motor Driver
 * MakeMindz.com
 *
 * Commands:  F = Forward   B = Backward
 *            L = Left      R = Right
 *            S = Stop      O = LED ON   f = LED OFF
 */

// Pin Definitions
const int motorPin1 = 13;  // IN1 — Left Forward
const int motorPin2 = 12;  // IN2 — Left Reverse
const int motorPin3 = 11;  // IN3 — Right Forward
const int motorPin4 = 10;  // IN4 — Right Reverse
const int ledPin    = 9;   // Status LED

void setup() {
  Serial.begin(9600);
  pinMode(motorPin1, OUTPUT);
  pinMode(motorPin2, OUTPUT);
  pinMode(motorPin3, OUTPUT);
  pinMode(motorPin4, OUTPUT);
  pinMode(ledPin,    OUTPUT);
  stopMotors();
  digitalWrite(ledPin, LOW);
}

void loop() {
  if (Serial.available() > 0) {
    char cmd = Serial.read();
    switch (cmd) {
      case 'F': moveForward();  break;
      case 'B': moveBackward(); break;
      case 'L': turnLeft();    break;
      case 'R': turnRight();   break;
      case 'S': stopMotors();  break;
      case 'O': digitalWrite(ledPin, HIGH); break;
      case 'f': digitalWrite(ledPin, LOW);  break;
      default: break;
    }
  }
}

void moveForward() {
  digitalWrite(motorPin1, HIGH);
  digitalWrite(motorPin2, LOW);
  digitalWrite(motorPin3, HIGH);
  digitalWrite(motorPin4, LOW);
}

void moveBackward() {
  digitalWrite(motorPin1, LOW);
  digitalWrite(motorPin2, HIGH);
  digitalWrite(motorPin3, LOW);
  digitalWrite(motorPin4, HIGH);
}

void turnLeft() {
  digitalWrite(motorPin1, LOW);
  digitalWrite(motorPin2, HIGH); // Left backward
  digitalWrite(motorPin3, HIGH); // Right forward
  digitalWrite(motorPin4, LOW);
}

void turnRight() {
  digitalWrite(motorPin1, HIGH); // Left forward
  digitalWrite(motorPin2, LOW);
  digitalWrite(motorPin3, LOW);
  digitalWrite(motorPin4, HIGH); // Right backward
}

void stopMotors() {
  digitalWrite(motorPin1, LOW);
  digitalWrite(motorPin2, LOW);
  digitalWrite(motorPin3, LOW);
  digitalWrite(motorPin4, LOW);
}

Bluetooth Commands

Send these single characters from any Bluetooth terminal app. Set the newline mode to None so only the character is transmitted.

Command	Action	Left Motors	Right Motors
F	Forward	↑ Forward	↑ Forward
B	Backward	↓ Reverse	↓ Reverse
L	Turn Left	↓ Reverse	↑ Forward
R	Turn Right	↑ Forward	↓ Reverse
S	Stop	■ Off	■ Off
O	LED ON	Status LED turns ON
f	LED OFF	Status LED turns OFF

Concepts Demonstrated

📡

UART Serial Comm

HC-05 sends characters to Arduino's hardware serial at 9600 baud.

🔀

H-Bridge Control

L298N drives motors bidirectionally using IN1–IN4 logic inputs.

⚙️

DC Motor Direction

Reversing HIGH/LOW on IN pins reverses motor rotation direction.

📶

Bluetooth SPP

HC-05 presents as a virtual COM port via Serial Port Profile.

🔄

Multi-Motor Sync

Tank-style steering via two independent L298N motor channels.

🛠️

Modular Code

Motor actions separated into helper functions for clean, extensible code.

Run the Simulation

🔬 Test before you build!

Simulate this exact circuit in CirkitDesigner — wire components virtually, run the code, and verify motor logic before soldering anything.

▶ Open Simulation →

✅

TipIn CirkitDesigner's Serial Monitor, send F, B, L, R, S and watch the IN pin states change in real time — no hardware needed.

Future Upgrades

Once you've built the base robot, these additions can turn it into an advanced autonomous platform:

HC-SR04 ultrasonic obstacle avoidance

IR line-following sensor array

ESP8266 / ESP32 WiFi + IoT control

Custom Android Bluetooth controller app

FPV WiFi camera module

PWM speed control via ENA/ENB pins

18650 Li-ion rechargeable battery pack

Autonomous navigation algorithm

→

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