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 transmission 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 compact and reliable Bluetooth device with the following key specifications:

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 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 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. Configure your microcontroller or serial terminal to match this rate.
• Pairing: The default pairing code is usually "1234" or "0000". Check the module's documentation if this does not work.
• Antenna Placement: Avoid placing the module near metal objects or other RF sources to ensure optimal signal strength.

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 for RXD)

#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 from your Bluetooth device to see it here.");
}

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

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 38400 bps for some modules in AT mode).
   • Check the wiring and ensure proper connections.

2. Bluetooth Device Cannot Pair with HC-05

   • Confirm the module is powered and in discoverable mode (LED blinking rapidly).
   • Verify the pairing code (default is "1234" or "0000").
   • Ensure the device is within the module's range.

3. Data Transmission Issues

   • Check the TXD and RXD connections. Ensure the RXD pin is not receiving more than 3.3V.
   • Verify that both devices are using the same baud rate.

4. Weak Signal or Connection Drops

   • Avoid placing the module near interference sources like Wi-Fi routers or metal objects.
   • Ensure the power supply is stable and sufficient.

Q: Can the HC-05 module work with 5V logic levels?
A: The TXD pin can output 5V logic, but the RXD pin is designed for 3.3V logic. Use a voltage divider or level shifter for safe operation.

Q: How do I switch between master and slave modes?
A: Use AT commands to configure the module. For example, send AT+ROLE=1 to set it as a master and AT+ROLE=0 to set it as a slave.

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

Q: Can I use the HC-05 with a Raspberry Pi?
A: Yes, the HC-05 can be connected to a Raspberry Pi via its UART pins. Ensure proper voltage level shifting for the RXD pin.