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 for enabling wireless communication between devices. Operating in the 2.4 GHz frequency range, the HC-05 supports both master and slave modes, making it suitable for a variety of applications. It is commonly used in embedded systems to connect microcontrollers, such as Arduino boards, to 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
• 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:

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 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 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 more than 3.3V. Use a voltage divider or level shifter if necessary.
• Baud Rate: The default baud rate is 9600 bps. Ensure your microcontroller's UART settings match this value.
• Connection Status: Use the STATE pin to monitor the connection status of the module.
• Range: Keep the module within 10 meters of the paired device 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); // Initialize hardware serial for debugging
  BTSerial.begin(9600); // Initialize Bluetooth serial communication

  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 data from HC-05
    Serial.print("Received: ");
    Serial.println(data); // Print received data to Serial Monitor
  }

  // Check if data is sent from 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
  }
}

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 value).
   • Check the wiring and ensure the TX and RX pins are correctly connected.

2. Bluetooth Device Not Discoverable

   • Ensure the module is powered on and in pairing mode (LED blinking rapidly).
   • Check for interference from other devices operating in the 2.4 GHz range.

3. Data Transmission Issues

   • Verify the TX and RX connections between the HC-05 and the microcontroller.
   • Ensure the baud rate matches on both the HC-05 and the microcontroller.

4. Short Range or Unstable Connection

   • Ensure there are no physical obstructions or interference sources between the HC-05 and the paired device.
   • Check the power supply for stability.

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 damage.

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 connect to multiple devices simultaneously?
A: No, the HC-05 supports only one connection at a time.

Q: How do I change the module's name or PIN?
A: Use AT commands in command mode:

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

This concludes the HC-05 documentation.