How to Use Bluetooth HC-05 Module: Examples, Pinouts, and Specs

The Bluetooth HC-05 Module, manufactured by ARDUINO (Part ID: MEGA), is a wireless communication module designed for short-range data transmission using Bluetooth technology. It is widely used in embedded systems to enable seamless communication between devices without the need for physical connections. The HC-05 module supports both master and slave modes, making it versatile for various applications.

• Wireless communication between microcontrollers and smartphones
• Remote control of robots and IoT devices
• Data logging and monitoring systems
• Home automation projects
• Serial communication between devices

The HC-05 module is a robust and reliable Bluetooth module with the following key specifications:

The HC-05 module has 6 pins, as described in the table below:

1. Power Supply: Connect the VCC pin to a 5V power source and the GND pin to ground.
2. UART Communication: Connect the TXD pin of the HC-05 to the RX pin of your microcontroller, and the RXD pin of the HC-05 to the TX pin of your microcontroller.
3. AT Command Mode: To configure the module, pull the EN (Key) pin HIGH and use AT commands via a serial terminal.
4. Pairing: The HC-05 module will appear as a Bluetooth device on your smartphone or computer. Pair it using the default PIN code (1234 or 0000).

• Use a voltage divider or level shifter on the RXD pin if your microcontroller operates at 5V logic levels to avoid damaging the module.
• Ensure the module is within the specified range (10 meters) for reliable communication.
• Avoid placing the module near sources of electromagnetic interference (e.g., motors, high-frequency circuits).
• Use AT commands to configure the module's baud rate, name, and mode (master/slave) as needed.

Below is an example of how to use the HC-05 module with an Arduino UNO to send and receive data via Bluetooth.

• HC-05 VCC → Arduino 5V
• HC-05 GND → Arduino GND
• HC-05 TXD → Arduino RX (Pin 0)
• HC-05 RXD → Arduino TX (Pin 1)

#include <SoftwareSerial.h>

// Create a SoftwareSerial object to communicate with HC-05
SoftwareSerial BTSerial(10, 11); // RX, TX pins for HC-05

void setup() {
  Serial.begin(9600); // Initialize Serial Monitor at 9600 baud
  BTSerial.begin(9600); // Initialize HC-05 at 9600 baud

  Serial.println("Bluetooth HC-05 Module Test");
  Serial.println("Send data via Bluetooth to see it here.");
}

void loop() {
  // Check if data is available from HC-05
  if (BTSerial.available()) {
    char data = BTSerial.read(); // Read data from HC-05
    Serial.print("Received: ");
    Serial.println(data); // Print received data to Serial Monitor
  }

  // Check if data is available from Serial Monitor
  if (Serial.available()) {
    char data = Serial.read(); // Read data from Serial Monitor
    BTSerial.write(data); // Send data to HC-05
  }
}

1. Module Not Powering On

   • Ensure the VCC pin is connected to a 5V power source.
   • Check for loose connections or damaged wires.

2. Unable to Pair with Device

   • Verify that the module is powered on and in discoverable mode (LED blinking rapidly).
   • Ensure the correct PIN code (1234 or 0000) is used during pairing.

3. No Data Transmission

   • Check the TXD and RXD connections between the HC-05 and the microcontroller.
   • Ensure the baud rate of the HC-05 matches the microcontroller's UART settings.

4. AT Commands Not Working

   • Confirm that the EN (Key) pin is pulled HIGH to enable AT command mode.
   • Use a serial terminal with the correct baud rate (default: 9600 bps).

Q: Can the HC-05 module be used with 3.3V microcontrollers?
A: Yes, the HC-05 module operates at 3.3V logic levels and is compatible with 3.3V microcontrollers.

Q: How do I reset the HC-05 module to factory settings?
A: Enter AT command mode and send the AT+ORGL command to reset the module to its default settings.

Q: Can the HC-05 module communicate with another HC-05 module?
A: Yes, configure one module as a master and the other as a slave using AT commands.

Q: What is the maximum data rate supported by the HC-05 module?
A: The HC-05 module supports a maximum baud rate of 1382400 bps, but the default is 9600 bps.