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

The HC-05 Bluetooth Module is a wireless communication module designed for short-range data transfer using Bluetooth technology. It is widely used in embedded systems, IoT projects, and robotics to enable seamless communication between devices. The module supports both master and slave modes, making it versatile for various applications.

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

The HC-05 module is a robust and easy-to-use Bluetooth device. 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 the 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 HC-05.
3. AT Command Mode: To configure the module, pull the EN pin HIGH and send AT commands via a serial terminal.
4. Normal Operation: Leave the EN pin LOW for standard Bluetooth communication.

• Voltage Levels: The HC-05 operates at 3.3V logic levels. Use a voltage divider or level shifter for the RXD pin if your microcontroller uses 5V logic.
• Baud Rate: Ensure the baud rate of your microcontroller matches the HC-05's default baud rate (9600 bps) or the configured baud rate.
• Connection Status: Use the STATE pin to monitor the connection status of the module.
• Avoid Interference: Operate the module in an environment with minimal RF interference for optimal performance.

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 if needed)

#include <SoftwareSerial.h>

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

void setup() {
  Serial.begin(9600); // Start Serial Monitor communication
  BTSerial.begin(9600); // Start Bluetooth communication at 9600 bps

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

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

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

1. Module Not Responding to AT Commands

   • Ensure the EN pin is pulled HIGH to enable AT command mode.
   • Verify the baud rate of the serial terminal matches the module's AT command baud rate (default: 38400 bps).

2. No Bluetooth Connection

   • Check if the module is powered correctly (LED should blink).
   • Ensure the device you are pairing with is discoverable and within range.

3. Data Transmission Issues

   • Verify the TXD and RXD connections are correct.
   • Use a voltage divider for the RXD pin if your microcontroller operates at 5V logic.

4. Unstable Connection

   • Minimize RF interference by keeping the module away from other wireless devices.
   • Ensure a stable power supply to the module.

Q: Can the HC-05 module be used with 5V logic microcontrollers?
A: Yes, but you must use a voltage divider or level shifter for the RXD pin to avoid damaging the module.

Q: How do I change the module's name or baud rate?
A: Enter AT command mode by pulling the EN pin HIGH and use AT commands like AT+NAME or AT+UART.

Q: What is the difference between master and slave modes?
A: In master mode, the HC-05 initiates connections with other devices. In slave mode, it waits for incoming connections.

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