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

The HC-05 is a Bluetooth module that allows for wireless communication between devices. It is a versatile and widely used component in embedded systems, enabling seamless connectivity between microcontrollers and Bluetooth-enabled devices such as smartphones, tablets, or computers. The module supports both master and slave modes, making it suitable for a variety of wireless communication applications.

• Wireless data transfer between microcontrollers and smartphones
• Remote control of devices via Bluetooth
• Home automation systems
• Robotics and IoT projects
• Wireless sensor networks

The HC-05 module is designed for ease of use and reliable communication. Below are its key technical specifications:

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

The HC-05 module is straightforward to use in a circuit. Below are the steps and best practices for integrating it into your project:

1. Power Supply: 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 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 to avoid damaging the RXD pin.
3. Enable AT Command Mode (Optional):
   • Pull the EN (Key) pin HIGH to enter AT command mode for configuration.
   • Use a serial terminal to send AT commands for setting parameters like baud rate, name, or mode (master/slave).

Below is an example of how to connect and use the HC-05 module with an Arduino UNO:

• 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 necessary)

#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
  }
}

• Voltage Levels: The RXD pin of the HC-05 is not 5V tolerant. Use a voltage divider or level shifter if your microcontroller operates at 5V logic levels.
• AT Command Mode: Use AT commands to configure the module before deployment. For example, you can set the module name, baud rate, and mode (master/slave).
• Connection Status: Use the STATE pin to monitor the connection status of the module.
• Avoid Pin Conflicts: If using the Arduino's hardware serial pins (0 and 1), ensure they are not used for other purposes like uploading code.

1. Module Not Responding to AT Commands:

   • Ensure the EN (Key) pin is pulled HIGH to enter AT command mode.
   • Verify the baud rate of the serial terminal matches the module's default baud rate (9600 bps).

2. No Data Transmission:

   • Check the wiring of the TXD and RXD pins. Ensure they are correctly connected to the RX and TX pins of the microcontroller.
   • Verify that the devices are paired and within range.

3. Unstable Connection:

   • Ensure there is no interference in the 2.4 GHz frequency band.
   • Check the power supply for stability and sufficient current.

4. Module Not Pairing:

   • Confirm that the module is in discoverable mode (flashing LED indicates this).
   • Ensure the correct pairing code (default: "1234" or "0000") is used.

Q1: Can the HC-05 module communicate with other Bluetooth versions?
Yes, the HC-05 is backward compatible with Bluetooth 1.1 and 1.2 devices.

Q2: How do I reset the HC-05 module?
To reset the module, disconnect and reconnect the power supply. Alternatively, use the AT command AT+RESET.

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

Q4: What is the difference between HC-05 and HC-06?
The HC-05 supports both master and slave modes, while the HC-06 operates only in slave mode.

By following this documentation, you can effectively integrate the HC-05 Bluetooth module into your projects and troubleshoot common issues.