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

The HC-05 is a Bluetooth module manufactured by BLUETOOTH, with the part ID HC-05. It is a versatile and widely used component that enables wireless communication between devices. Operating in the 2.4 GHz frequency range, the HC-05 is designed for seamless integration into embedded systems, allowing microcontrollers to communicate with smartphones, laptops, or other Bluetooth-enabled devices.

• Wireless data transfer between microcontrollers and smartphones
• Remote control of devices via Bluetooth
• Home automation systems
• Robotics and IoT projects
• Serial communication in embedded systems

The HC-05 module is a Class 2 Bluetooth device with a range of approximately 10 meters. 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 the microcontroller and the RXD pin of the HC-05 to the TX pin of the microcontroller. Use a voltage divider if the microcontroller operates at 5V logic levels to avoid damaging the RXD pin.
3. AT Command Mode: To configure the module, pull the EN (Key) pin HIGH and communicate with the module using 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 voltages higher than 3.3V. Use a voltage divider or level shifter if necessary.
• Baud Rate: The default baud rate is 9600 bps. Configure your microcontroller or serial terminal to match this rate.
• Pairing: The default pairing code for the HC-05 is usually "1234" or "0000". This can be changed using AT commands.
• Antenna Placement: Avoid placing the module near metal objects or other RF sources to minimize interference.

Below is an example of how to use the HC-05 with an Arduino UNO to send and receive data:

• 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 if needed)

#include <SoftwareSerial.h>

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

void setup() {
  // Start the hardware serial communication
  Serial.begin(9600); 
  // Start the Bluetooth serial communication
  BTSerial.begin(9600); 

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

void loop() {
  // Check if data is available from the Bluetooth module
  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
  }
}

1. Module Not Responding to AT Commands

   • Ensure the EN (Key) pin is pulled HIGH.
   • Verify the baud rate is set to 9600 bps (or the configured rate).
   • Check the wiring and ensure the TX and RX pins are correctly connected.

2. Bluetooth Device Not Pairing

   • Confirm the module is powered and in discoverable mode (blinking LED).
   • Verify the pairing code (default is "1234" or "0000").
   • Ensure the device is within the 10-meter range.

3. Data Transmission Issues

   • Check for proper voltage levels on the RXD pin.
   • Ensure the baud rate matches between the HC-05 and the microcontroller.
   • Minimize interference from other RF devices.

Q: Can the HC-05 be used in master mode?
A: Yes, the HC-05 can operate in both master and slave modes. Use AT commands to configure the mode.

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.

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

Q: Can the HC-05 communicate with BLE devices?
A: No, the HC-05 uses Bluetooth 2.0 and is not compatible with Bluetooth Low Energy (BLE) devices.