Bluetooth-controlled RC car with Arduino and L298N

A Bluetooth-controlled RC car is a classic robotics project for getting comfortable with DC motors, H-bridges, and wireless communication — no custom app needed, just any off-the-shelf Bluetooth serial controller app and a few lines of Arduino code.

How it works

1. Your phone pairs over Bluetooth with the HC-05 module (acting as a wireless serial port).
2. The controller app sends a single command character each time a button is pressed: F (forward), B (backward), L (left), R (right), S (stop).
3. The Arduino reads that character from Serial (wired to the HC-05) and maps it to a combination of signals driving two DC motors through an L298N H-bridge.
4. Motor speed is set with a PWM signal on the L298N’s ENA/ENB pins.

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<text x="285" y="135" text-anchor="middle" class="label">HC-05 -> Arduino</text>

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<text x="510" y="65" text-anchor="middle" class="label">Read command, pick direction</text>

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<text x="510" y="205" text-anchor="middle" class="label">L298N drives both motors</text>

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Parts list

• Arduino Uno
• HC-05 Bluetooth module
• L298N H-bridge motor driver (drives 2 DC motors)
• 2 DC motors + wheels, a 2- or 4-wheel robot chassis
• A separate battery for the motors (18650 cell or a 9V-12V pack, not shared with the Arduino’s supply)
• Two resistors (1k ohm and 2k ohm) for a voltage divider on the HC-05’s RX pin
• Any Bluetooth serial controller app on your phone (e.g. “Arduino Bluetooth Controller” or “Serial Bluetooth Terminal”)

An important wiring detail

The HC-05 runs at 3.3V logic, but the Arduino Uno’s TX pin outputs 5V. Wiring Arduino’s TX directly into HC-05’s RX without stepping the voltage down can degrade or damage the module over time — use a voltage divider:

Arduino TX (5V) --[1k ohm]--+--[2k ohm]--- GND
                             |
                          HC-05 RX (~3.3V)

Sample code

#include <SoftwareSerial.h>

SoftwareSerial bluetooth(10, 11); // RX, TX wired to the HC-05

// L298N direction control pins
const int IN1 = 2, IN2 = 3; // left motor
const int IN3 = 4, IN4 = 5; // right motor
const int ENA = 9;  // PWM speed for the left motor
const int ENB = 6;  // PWM speed for the right motor
const int SPEED = 200; // 0-255

void goForward() {
  digitalWrite(IN1, HIGH); digitalWrite(IN2, LOW);
  digitalWrite(IN3, HIGH); digitalWrite(IN4, LOW);
}
void goBackward() {
  digitalWrite(IN1, LOW); digitalWrite(IN2, HIGH);
  digitalWrite(IN3, LOW); digitalWrite(IN4, HIGH);
}
void turnLeft() {
  digitalWrite(IN1, LOW); digitalWrite(IN2, LOW);
  digitalWrite(IN3, HIGH); digitalWrite(IN4, LOW);
}
void turnRight() {
  digitalWrite(IN1, HIGH); digitalWrite(IN2, LOW);
  digitalWrite(IN3, LOW); digitalWrite(IN4, LOW);
}
void stopCar() {
  digitalWrite(IN1, LOW); digitalWrite(IN2, LOW);
  digitalWrite(IN3, LOW); digitalWrite(IN4, LOW);
}

void setup() {
  bluetooth.begin(9600);
  pinMode(IN1, OUTPUT); pinMode(IN2, OUTPUT);
  pinMode(IN3, OUTPUT); pinMode(IN4, OUTPUT);
  pinMode(ENA, OUTPUT); pinMode(ENB, OUTPUT);
  analogWrite(ENA, SPEED);
  analogWrite(ENB, SPEED);
  stopCar();
}

void loop() {
  if (bluetooth.available()) {
    char command = bluetooth.read();
    switch (command) {
      case 'F': goForward(); break;
      case 'B': goBackward(); break;
      case 'L': turnLeft(); break;
      case 'R': turnRight(); break;
      case 'S': stopCar(); break;
    }
  }
}

Pair the HC-05 with your phone first through Bluetooth settings (the default PIN is usually 1234 or 0000), then open your controller app and map its buttons to send the F/B/L/R/S characters.

Common pitfalls

• Skipping the voltage divider on RX: running the HC-05’s RX at 5V long-term can shorten its lifespan or damage it outright — always step it down as shown above.
• Sharing power between the Arduino and the motors: DC motors generate back-EMF spikes when starting or reversing suddenly, which can cause noise or reset the Arduino — power the motors from a separate battery and only share ground.
• Forgetting a common ground between the Arduino, HC-05, and L298N — this is the most common reason commands “send fine” but the car never moves.
• SoftwareSerial pin conflicts: if you’re on a Mega or Leonardo instead of an Uno, consider using a hardware Serial1 port instead of SoftwareSerial for more reliable behavior at higher baud rates.

Where to go from here

Add an HC-SR04 ultrasonic sensor up front so the car automatically stops near obstacles, or swap the HC-05 for an ESP32 to control it over WiFi with a custom mobile app that has a virtual joystick instead of just five buttons.