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

The HC-05 Bluetooth Module, manufactured by DSD TECH (Part ID: Bluetooth), is a versatile wireless communication module designed for short-range data transmission. It operates using Bluetooth technology and is widely used in embedded systems to enable wireless communication between devices. The module supports both master and slave modes, making it suitable for a variety of applications.

• Wireless communication between microcontrollers and smartphones
• Remote control of devices (e.g., robots, home automation systems)
• Data logging and wireless data transfer
• Serial communication replacement in embedded systems
• IoT (Internet of Things) applications

The HC-05 Bluetooth Module is designed to operate efficiently in a wide range of applications. Below are its key technical details:

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

The HC-05 Bluetooth Module is easy to integrate into a circuit. Follow the steps below to use it effectively:

1. Power the Module: Connect the VCC pin to a 3.3V or 5V power source and the GND pin to ground.
2. Connect TXD and RXD:
   • Connect the TXD pin of the HC-05 to the RX pin of the microcontroller.
   • Connect 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.
3. Optional Connections:
   • Connect the EN/KEY pin to a GPIO pin of the microcontroller if you need to switch between command and data modes.
   • Use the STATE pin to monitor the connection status.

The HC-05 can be configured using AT commands in command mode. To enter command mode:

• Pull the EN/KEY pin HIGH before powering the module.
• Use a serial terminal to send AT commands at the default baud rate of 9600 bps.

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

• Connect VCC to the Arduino's 5V pin.
• Connect GND to the Arduino's GND pin.
• Connect TXD to the Arduino's RX pin (pin 0).
• Connect RXD to the Arduino's TX pin (pin 1) through a voltage divider.

// HC-05 Bluetooth Module Example with Arduino UNO
// This code sends and receives data via the HC-05 module.

#include <SoftwareSerial.h>

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

void setup() {
  // Initialize hardware serial for debugging
  Serial.begin(9600);
  Serial.println("HC-05 Bluetooth Module Test");

  // Initialize Bluetooth serial communication
  BTSerial.begin(9600); // Default baud rate for HC-05
  Serial.println("Bluetooth module ready");
}

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 received 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
  }
}

• Voltage Levels: The RXD pin is not 5V tolerant. Use a voltage divider or level shifter if your microcontroller operates at 5V logic.
• Baud Rate: Ensure the baud rate of the microcontroller matches the HC-05's baud rate.
• Command Mode: Always pull the EN/KEY pin HIGH before powering the module to enter command mode.
• Range: Keep the module within its specified range (10 meters) for reliable communication.

1. Module Not Responding to AT Commands:

   • Ensure the EN/KEY pin is HIGH before powering the module.
   • Verify the baud rate is set to 9600 bps in your serial terminal.

2. No Data Transmission:

   • Check the connections between the HC-05 and the microcontroller.
   • Ensure the TXD and RXD pins are correctly connected (crossed).

3. Unstable Connection:

   • Reduce the distance between the HC-05 and the paired device.
   • Avoid interference from other 2.4 GHz devices.

4. Module Not Pairing:

   • Ensure the module is in discoverable mode (LED blinking rapidly).
   • Verify the pairing code (default is 1234 or 0000).

Q1: Can the HC-05 work with 5V logic levels?
A1: The TXD pin can output 5V logic, but the RXD pin is not 5V tolerant. Use a voltage divider for safe operation.

Q2: How do I reset the HC-05 to factory settings?
A2: Enter command mode and send the AT+ORGL command to reset the module to its default settings.

Q3: Can I use the HC-05 for audio transmission?
A3: No, the HC-05 is designed for serial data communication and does not support audio transmission.

Q4: How do I change the module's name or PIN?
A4: Use the following AT commands in command mode:

• Change name: AT+NAME=YourName
• Change PIN: AT+PSWD=YourPIN

By following this documentation, you can effectively integrate and troubleshoot the HC-05 Bluetooth Module in your projects.