HC-05 Bluetooth Module - Normal

The HC-05 Bluetooth module is widely used in applications such as wireless headsets, game controllers, wireless mice, keyboards, and many other consumer electronic devices. It operates based on the IEEE 802.15.1 Bluetooth standard, enabling the creation of a Wireless Personal Area Network (PAN). The module uses Frequency-Hopping Spread Spectrum (FHSS) technology to transmit data wirelessly.

Communication with other devices is done through serial communication, as the HC-05 connects to microcontrollers via the USART (UART) interface.

Specifications

• Operating voltage: 3.6 V – 6 V (connected to the VCC pin)
• Communication logic level: 3.3 V (5 V tolerant)
• Current consumption: approximately 50 mA
• Bluetooth class: Class 2
• Maximum transmission power: +4 dBm
• Communication range: up to 10 meters
• Default pairing password: 1234
• Bluetooth standard: Bluetooth 2.0 + EDR
• Supported profile: SPP (Serial Port Profile) with AT command configuration
• Communication interface: UART (RX, TX)
• Dimensions: 39 × 16 mm

Bluetooth serial modules like HC-05 allow serial-based devices to communicate wirelessly using Bluetooth technology.

HC-05 Pin Description

The HC-05 module has six pins:

• Key / EN: Used to switch the module into AT command mode. When this pin is set HIGH, the module enters command mode; otherwise, it operates in data mode. The default baud rate is 38400 bps in command mode and 9600 bps in data mode.
  • Data Mode: Used for exchanging data between devices.
  • Command Mode: Used to configure the module using AT commands.
• VCC: Power supply pin (3.3 V or 5 V).
• GND: Ground pin.
• TXD: Transmits serial data received wirelessly by the Bluetooth module.
• RXD: Receives serial data that will be sent wirelessly via Bluetooth.
• State: Indicates the connection status of the module.

HC-05 Module Information

The HC-05 module includes a red LED that indicates its connection status. When the module is not connected, the LED blinks continuously. Once a Bluetooth connection is established, the blinking slows to once every two seconds.

Although the HC-05 operates internally at 3.3 V, it can safely accept a 5 V power supply due to its built-in voltage regulator. The TX and RX pins operate at 3.3 V logic levels, which are typically recognized by most microcontrollers. Therefore, no level shifting is required from the HC-05 to the microcontroller. However, level shifting is required when sending signals from a 5 V microcontroller to the HC-05 RX pin.

Pairing HC-05 with a Smartphone

1. Enable Bluetooth on your smartphone and search for nearby devices.
2. Select the device named HC-05.
3. Pair the device using the default PIN: 1234 or 0000.
4. On a PC, open a serial terminal program (such as Tera Term or RealTerm) and select the correct COM port with a baud rate of 9600 bps.
5. Open a Bluetooth terminal application on the smartphone and connect to the paired HC-05 device.

Once connected, data typed on the smartphone is transmitted wirelessly to the HC-05 and forwarded via serial communication to the PC, where it appears on the terminal. Similarly, data sent from the PC can be received on the smartphone.

Command Mode

Command mode is used to modify the HC-05 configuration, such as changing the device name, baud rate, or pairing password. This is done using AT commands.

To enter command mode:

• Connect the Key pin to HIGH (VCC).
• Use a baud rate of 38400 bps, which is the default for AT command mode.

The HC-05 must be connected to a PC through a USB-to-serial converter, and AT commands are sent via a serial terminal application.