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

The HC-05 is a Bluetooth module manufactured by Arduino (Part ID: Bluetooth) that enables wireless communication between devices. It is a versatile and cost-effective solution for implementing Bluetooth connectivity in various projects. The module supports both master and slave modes, making it suitable for a wide range of applications, including Internet of Things (IoT) devices, robotics, and wireless data transfer systems.

• Wireless communication between microcontrollers and smartphones
• IoT devices for remote monitoring and control
• Robotics projects requiring wireless control
• Serial data transfer between devices
• Home automation systems

The HC-05 module is designed to operate efficiently in embedded systems and offers the following key 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. Follow the steps below to integrate it into your project:

1. Wiring the Module:

   • Connect the VCC pin of the HC-05 to the 5V pin on the Arduino.
   • Connect the GND pin of the HC-05 to the GND pin on the Arduino.
   • Connect the TXD pin of the HC-05 to the RX pin (pin 0) on the Arduino.
   • Connect the RXD pin of the HC-05 to the TX pin (pin 1) on the Arduino. Use a voltage divider (e.g., 1kΩ and 2kΩ resistors) to step down the Arduino's 5V TX signal to 3.3V for the HC-05's RXD pin.

2. Configuring the Module:

   • By default, the HC-05 operates in slave mode. To configure it as a master or change settings, use AT commands in command mode.
   • To enter command mode, set the EN pin high (connect it to 3.3V) before powering the module.

3. Arduino Code Example: Below is an example code to send and receive data between the Arduino and a Bluetooth-enabled device (e.g., smartphone):

   #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
     Serial.println("HC-05 Bluetooth Module Initialized");
   }
   
   void loop() {
     // Check if data is received from Bluetooth
     if (BTSerial.available()) {
       char data = BTSerial.read(); // Read the incoming data
       Serial.print("Received: ");
       Serial.println(data); // Print the received data to Serial Monitor
     }
   
     // Check if data is sent from Serial Monitor
     if (Serial.available()) {
       char data = Serial.read(); // Read the data from Serial Monitor
       BTSerial.write(data); // Send the data to the Bluetooth device
       Serial.print("Sent: ");
       Serial.println(data); // Print the sent data to Serial Monitor
     }
   }
   

• Voltage Levels: The RXD pin of the HC-05 is not 5V tolerant. Always use a voltage divider or level shifter to step down the Arduino's 5V TX signal to 3.3V.
• Baud Rate: Ensure the baud rate of the HC-05 matches the baud rate of the microcontroller for proper communication.
• Command Mode: Use command mode to configure the module (e.g., change the name, password, or mode). Enter command mode by setting the EN pin high before powering the module.
• Range: The module's range is up to 10 meters in an unobstructed environment. Walls and other obstacles may reduce the range.

1. No Response from the Module:

   • Ensure the VCC and GND pins are properly connected.
   • Verify that the RXD and TXD pins are correctly wired (crossed connections: TXD to RX, RXD to TX).
   • Check the baud rate settings in your code and ensure they match the module's default (9600 bps).

2. Data Not Transmitting or Receiving:

   • Confirm that the Bluetooth device is paired with the HC-05.
   • Check for loose connections or incorrect wiring.
   • Ensure the module is in the correct mode (data mode for communication).

3. Unable to Enter Command Mode:

   • Make sure the EN pin is set high before powering the module.
   • Use a terminal program (e.g., Arduino Serial Monitor) to send AT commands. Ensure "No line ending" is selected in the Serial Monitor settings.

Q1: Can the HC-05 connect to multiple devices simultaneously?
A1: No, the HC-05 can only connect to one device at a time.

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 with a 3.3V microcontroller?
A3: Yes, the HC-05 operates at 3.3V logic levels and is compatible with 3.3V microcontrollers.

Q4: What is the difference between master and slave modes?
A4: In master mode, the HC-05 initiates connections with other Bluetooth devices. In slave mode, it waits for incoming connection requests.