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

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

• Wireless communication between microcontrollers and devices
• Remote control systems
• Data logging and monitoring
• Home automation
• Robotics and IoT projects
• Wireless sensor networks

The HC-05 Bluetooth Module is designed to provide reliable and efficient communication. 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 Supply: Connect the VCC pin to a 3.3V or 5V power source and the GND pin to ground.
2. UART 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.
3. AT Command Mode (Optional): To configure the module, pull the EN/KEY pin HIGH and use AT commands via a serial terminal.

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

#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 for debugging
  Serial.begin(9600);
  Serial.println("HC-05 Bluetooth Module Test");

  // Start the software serial communication with HC-05
  BTSerial.begin(9600); // Default baud rate of HC-05
  Serial.println("Enter AT commands:");
}

void loop() {
  // Check if data is available from HC-05
  if (BTSerial.available()) {
    char c = BTSerial.read();
    Serial.write(c); // Forward data to Serial Monitor
  }

  // Check if data is available from Serial Monitor
  if (Serial.available()) {
    char c = Serial.read();
    BTSerial.write(c); // Forward data to HC-05
  }
}

• Voltage Levels: The RXD pin is not 5V tolerant. Use a voltage divider or level shifter if connecting to a 5V microcontroller.
• AT Command Mode: Use AT commands to configure the module (e.g., change baud rate, set name, or switch between master/slave modes).
• Connection Status: Monitor the STATE pin to determine if the module is connected to a device.
• Avoid Noise: Use decoupling capacitors near the power pins to reduce noise and ensure stable operation.

1. Module Not Responding to AT Commands

   • Ensure the EN/KEY pin is pulled HIGH.
   • Verify the baud rate is set to 9600 bps (default for AT mode).
   • Check wiring connections for errors.

2. No Data Transmission

   • Confirm the TXD and RXD pins are correctly connected to the microcontroller.
   • Ensure the paired device is within the module's range (10 meters).

3. Unstable Connection

   • Check for power supply stability. Use a regulated 3.3V or 5V source.
   • Avoid interference from other Bluetooth devices operating nearby.

4. Cannot Pair with Another Device

   • Ensure the module is in discoverable mode (flashing LED indicates this).
   • Verify the pairing code (default is usually 1234 or 0000).

Q: Can the HC-05 module work with 5V logic levels?
A: The TXD pin can output 5V logic, but the RXD pin is not 5V tolerant. Use a voltage divider or level shifter for safe operation with 5V microcontrollers.

Q: How do I reset the HC-05 module?
A: Disconnect the power supply, then reconnect it. Alternatively, use the AT command AT+RESET.

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 profiles.

Q: How do I switch between master and slave modes?
A: Use the AT command AT+ROLE=1 for master mode and AT+ROLE=0 for slave mode.

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