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

The HC-05 Bluetooth module is a widely-used wireless communication device that enables Bluetooth connectivity for electronic projects. It operates in both master and slave modes, allowing it to either initiate a connection or accept connections from other Bluetooth devices. This versatility makes it ideal for a range of applications, including robotics, home automation, and Internet of Things (IoT) projects.

• Bluetooth Technology: Bluetooth 2.0+EDR (Enhanced Data Rate)
• Frequency: 2.4GHz ISM band
• Modulation: GFSK (Gaussian Frequency Shift Keying)
• Supply Voltage: 3.3V to 6V (Typically 5V compatible)
• Operating Current: 30mA (pairing), 10mA (communication)
• Communication Range: Up to 10 meters (in open space)
• Serial Interface: Asynchronous, full-duplex, serial port profile (SPP)
• Default Baud Rate: 9600,8,N,1 (can be configured)
• Security: Authentication and encryption
• Profiles: Bluetooth Serial Port

1. Power Connections: Connect the VCC pin to a 5V supply and the GND pin to the ground.
2. Data Connections: Connect the TXD pin of the HC-05 to the RX pin of the host microcontroller (e.g., Arduino UNO) and the RXD pin to the TX pin of the microcontroller.
3. AT Command Mode: To enter AT command mode for configuration, pull the KEY pin HIGH, power on the HC-05, and use a serial monitor to send commands.

• Ensure that the power supply is stable and within the specified voltage range.
• Use a voltage divider or a level shifter if the host microcontroller operates at a different logic level than the HC-05.
• When pairing with other devices, ensure that the HC-05 is in the appropriate mode (master or slave).
• Avoid placing the module near sources of interference, such as Wi-Fi routers or microwave ovens.

#include <SoftwareSerial.h>

SoftwareSerial BTSerial(10, 11); // RX | TX

void setup() {
  pinMode(9, OUTPUT);  // KEY pin if needed for AT commands
  digitalWrite(9, HIGH); // Enable AT command mode
  Serial.begin(9600);
  BTSerial.begin(38400);  // HC-05 default speed in AT command mode
  Serial.println("Enter AT commands:");
}

void loop() {
  // Keep reading from HC-05 and send to Arduino Serial Monitor
  if (BTSerial.available())
    Serial.write(BTSerial.read());

  // Keep reading from Arduino Serial Monitor and send to HC-05
  if (Serial.available())
    BTSerial.write(Serial.read());
}

• Module not responding: Ensure that the module is powered correctly and that the TX/RX connections are correct.
• Cannot pair or connect: Make sure the device is in the correct mode and is discoverable. Also, check the proximity of the devices.
• Unstable connection: Interference from other devices can cause instability. Try changing the location of the HC-05.

• Power Cycle: If the module is unresponsive, try disconnecting and reconnecting the power.
• LED Indicator: The STATE pin can be used to determine the connection status through the onboard LED.
• AT Commands: Use AT commands to check and configure the settings of the HC-05.

Q: How do I change the baud rate of the HC-05? A: Enter AT command mode and use the command AT+UART=<baud rate>,<stop bits>,<parity> to set the desired baud rate.

Q: Can the HC-05 be used to communicate with smartphones? A: Yes, the HC-05 can communicate with smartphones that have Bluetooth capabilities.

Q: What is the default password for pairing the HC-05? A: The default password is usually '1234' or '0000'.