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

The HC-05 is a Bluetooth module designed and manufactured by Arduino to enable wireless communication between devices. It supports both master and slave modes, making it a versatile solution for a wide range of applications. The module is commonly used to connect microcontrollers, such as Arduino boards, to smartphones, computers, or other Bluetooth-enabled devices. Its ease of use and reliable performance make it a popular choice for wireless communication in IoT projects, robotics, and home automation systems.

• Wireless communication between microcontrollers and smartphones
• Remote control of robots or IoT devices
• Data logging and monitoring via Bluetooth
• Home automation systems
• Wireless sensor networks

The HC-05 Bluetooth module is a compact and efficient device with the following key specifications:

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

1. Wiring the HC-05 to an Arduino UNO:

   • Connect the VCC pin of the HC-05 to the 5V pin of the Arduino.
   • Connect the GND pin of the HC-05 to the GND pin of the Arduino.
   • Connect the TXD pin of the HC-05 to the RX pin of the Arduino (pin 0).
   • Connect the RXD pin of the HC-05 to the TX pin of the Arduino (pin 1).
   • Optionally, connect the EN pin to a digital pin on the Arduino for mode switching.

2. Configuring the HC-05:

   • By default, the HC-05 operates in slave mode with a baud rate of 9600 bps.
   • To change settings (e.g., baud rate or mode), enter AT command mode by setting the EN pin HIGH.

3. Example Circuit Diagram:

   Arduino UNO          HC-05
   ------------------------------
   5V                -> VCC
   GND               -> GND
   RX (Pin 0)        -> TXD
   TX (Pin 1)        -> RXD
   

The following code demonstrates how to send and receive data using the HC-05 module:

#include <SoftwareSerial.h>

// Create a SoftwareSerial object to communicate with the HC-05
SoftwareSerial Bluetooth(10, 11); // RX = Pin 10, TX = Pin 11

void setup() {
  // Initialize serial communication with the computer
  Serial.begin(9600);
  // Initialize serial communication with the HC-05
  Bluetooth.begin(9600);

  Serial.println("HC-05 Bluetooth Module Initialized");
  Serial.println("You can now send and receive data.");
}

void loop() {
  // Check if data is available from the HC-05
  if (Bluetooth.available()) {
    char received = Bluetooth.read(); // Read the incoming data
    Serial.print("Received: ");
    Serial.println(received); // Print the received data to the Serial Monitor
  }

  // Check if data is available from the Serial Monitor
  if (Serial.available()) {
    char toSend = Serial.read(); // Read the data from the Serial Monitor
    Bluetooth.write(toSend); // Send the data to the HC-05
    Serial.print("Sent: ");
    Serial.println(toSend); // Print the sent data to the Serial Monitor
  }
}

• Use a voltage divider or level shifter on the RXD pin if the microcontroller operates at 5V logic levels, as the HC-05 operates at 3.3V logic.
• Avoid connecting the HC-05's TXD pin directly to a 5V microcontroller without proper interfacing.
• Ensure the module is not in AT command mode when transmitting or receiving data.
• Keep the module within the specified communication range for reliable performance.

1. Issue: The HC-05 is not responding to AT commands.

   • Solution: Ensure the EN pin is HIGH to enter AT command mode. Also, verify the baud rate is set to 38400 bps in AT mode.

2. Issue: The module is not pairing with a Bluetooth device.

   • Solution: Check if the module is in slave mode. Ensure the pairing device is within range and the correct PIN (default: 1234) is used.

3. Issue: Data transmission is unreliable or slow.

   • Solution: Verify the baud rate matches between the HC-05 and the microcontroller. Ensure there are no obstructions or interference in the communication range.

4. Issue: The HC-05 is not powering on.

   • Solution: Confirm the VCC pin is connected to a 3.3V or 5V power source. Check all connections for loose wires.

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

• Q: How do I reset the HC-05 to factory settings?
  A: Enter AT command mode and send the AT+ORGL command to reset the module.

• Q: What is the default name of the HC-05 module?
  A: The default name is usually "HC-05," but it can be changed using AT commands.

• Q: Can the HC-05 be used for audio transmission?
  A: No, the HC-05 is designed for serial data communication and does not support audio transmission.