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

The HC-05 Bluetooth Serial Module, manufactured by Guangzhou HC Information Technology Co., Ltd., is a versatile and widely used Bluetooth module designed for wireless communication. Operating in the 2.4 GHz frequency range, it enables seamless data exchange between devices such as microcontrollers, smartphones, and other Bluetooth-enabled systems. The HC-05 supports both master and slave modes, making it suitable for a variety of embedded applications.

• Wireless communication between microcontrollers and smartphones
• Remote control of devices via Bluetooth
• Data logging and monitoring systems
• Home automation projects
• Robotics and IoT applications

The HC-05 module is designed to provide reliable and efficient Bluetooth communication. Below are its key technical details:

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

1. Powering the Module: Connect the VCC pin to a 3.3V or 5V power source and the GND pin to ground.
2. Serial 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. Use a voltage divider if your microcontroller operates at 5V logic levels to avoid damaging the RXD pin.
3. AT Command Mode: To configure the module (e.g., change the baud rate or name), pull the EN (Key) pin HIGH and send AT commands via a serial terminal.
4. Normal Operation: Leave the EN (Key) pin LOW for standard Bluetooth communication.

• Voltage Levels: Ensure the RXD pin does not receive signals higher than 3.3V. Use a voltage divider or level shifter if necessary.
• Antenna Placement: Avoid placing the module near metal objects or other RF sources to minimize interference.
• Pairing: The default pairing code for the HC-05 is usually "1234" or "0000". Check the module's documentation if this does not work.
• Baud Rate: The default baud rate is 9600 bps. Ensure your microcontroller's UART settings match this value.

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) (use a voltage divider for RXD)

#include <SoftwareSerial.h>

// Define RX and TX pins for SoftwareSerial
SoftwareSerial BTSerial(10, 11); // RX = Pin 10, TX = Pin 11

void setup() {
  // Initialize serial communication with the HC-05
  BTSerial.begin(9600); // Default baud rate of HC-05
  Serial.begin(9600);   // Serial monitor baud rate

  Serial.println("HC-05 Bluetooth Module Test");
}

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

  // Check if data is available from the Serial Monitor
  if (Serial.available()) {
    char data = Serial.read();   // Read data from Serial Monitor
    BTSerial.write(data);        // Send data to HC-05
    Serial.print("Sent: ");
    Serial.println(data);        // Print sent data to Serial Monitor
  }
}

1. Module Not Pairing with Device:

   • Ensure the HC-05 is powered on and in discoverable mode (LED blinking rapidly).
   • Verify the pairing code (default is "1234" or "0000").
   • Check if the device supports Bluetooth 2.0.

2. No Data Transmission:

   • Confirm the TXD and RXD connections are correct.
   • Ensure the baud rate of the HC-05 matches the microcontroller's UART settings.
   • Check for loose or faulty connections.

3. AT Commands Not Working:

   • Ensure the EN (Key) pin is pulled HIGH to enter AT command mode.
   • Use a serial terminal with "No Line Ending" or "Carriage Return" settings as required.

4. Short Communication Range:

   • Avoid obstructions and interference from other RF devices.
   • Ensure the module's antenna is not damaged or obstructed.

Q: Can the HC-05 module communicate with Bluetooth 4.0 devices?
A: Yes, the HC-05 is backward compatible with Bluetooth 4.0 devices, but it operates at Bluetooth 2.0 standards.

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

Q: Can I use the HC-05 for audio transmission?
A: No, the HC-05 is designed for serial data communication and does not support audio transmission.

Q: What is the difference between HC-05 and HC-06?
A: The HC-05 supports both master and slave modes, while the HC-06 operates only in slave mode.