How to Use bluetooth: Examples, Pinouts, and Specs

The HC-05 is a widely used Bluetooth module that enables wireless communication between devices. It operates in the 2.4 GHz ISM band and can be used to establish a serial connection between microcontrollers, computers, smartphones, and other Bluetooth-enabled devices. Common applications include wireless control systems, data logging, and user interface components for various electronic projects.

• Bluetooth Technology: Bluetooth 2.0+EDR (Enhanced Data Rate)
• Frequency: 2.4 to 2.485 GHz ISM band
• Operating Voltage: 3.3V to 6V (Typically 5V compatible)
• Operating Current: 30mA (pairing mode), 10mA (communication mode)
• Communication Interface: Serial (UART)
• Default Baud Rate: 9600 bps (configurable)
• Security: Authentication and encryption
• Range: Up to 10 meters (Class 2)

1. Power Supply: Connect the VCC pin to a 5V output on your microcontroller board and the GND pin to a ground pin.
2. Serial Connection: Connect the TXD pin of the HC-05 to the RXD pin of your microcontroller, and the RXD pin of the HC-05 to the TXD pin of your microcontroller.
3. Mode Selection: The KEY pin can be left disconnected for normal operation or connected to a digital pin on your microcontroller for mode switching.

• Ensure that the power supply is stable and within the specified voltage range.
• Use a voltage divider or level shifter if your microcontroller operates at a different logic level than the HC-05.
• Pairing and connection procedures should be followed as per the HC-05 datasheet.
• Avoid placing the module near sources of interference or physical obstructions that may reduce its range.

#include <SoftwareSerial.h>

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

void setup() {
  pinMode(9, OUTPUT);  // KEY pin if needed for mode switching
  digitalWrite(9, LOW); // Normal operation mode
  Serial.begin(9600);
  BTSerial.begin(9600);  // HC-05 default speed in AT command more
}

void loop() {
  // Read from HC-05 and send to the Arduino Serial Monitor
  if (BTSerial.available()) {
    char c = BTSerial.read();
    Serial.write(c);
  }

  // Read from the Serial Monitor and send to HC-05
  if (Serial.available()) {
    char c = Serial.read();
    BTSerial.write(c);
  }
}

• Device not pairing: Ensure the module is in pairing mode and that the device you are trying to pair is within range.
• Serial communication not working: Check the wiring, especially the TX and RX connections. Also, verify the baud rate settings.
• Intermittent connection: This could be due to power supply issues or environmental interference. Ensure a stable power source and clear line of sight.

• Reset the module: Sometimes simply resetting the HC-05 can resolve connection issues.
• AT Commands: Use AT commands to configure the HC-05 settings such as baud rate, device name, and pairing password.
• LED Indicator: The STATE pin can be monitored for connection status, which can be helpful for debugging.

Q: How do I change the baud rate of the HC-05? A: You can change the baud rate using AT commands. Enter AT mode by pulling the KEY pin high and use the command AT+UART=<baud rate>,<stop bits>,<parity> to set the desired baud rate.

Q: Can I connect multiple devices to the HC-05 at the same time? A: No, the HC-05 can only be connected to one device at a time in slave mode.

Q: How do I know if my HC-05 is in AT command mode? A: The HC-05 enters AT command mode when the KEY pin is held high on power-up. The LED will blink in a different pattern compared to normal mode, typically a slower blink rate.

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