HC-05 Bluetooth module

The HC-05 has two operating modes, one is that the Data mode during which it can send and receive data from other Bluetooth devices and therefore the other is that the AT Command mode where the default device settings are often changed. we will operate the device in either of those two modes by using the key pin as explained within the pin description.

It is very easy to pair the HC-05 module with microcontrollers because it operates using the interface Protocol (SPP). The module with +5V and connect the Rx pin of the module to the Tx of MCU and Tx pin of the module to Rx of MCU as shown within the figure below. During power up the key pin is often grounded to enter into Command mode, if left free it’ll by default enter into the info model.

Password Details:

Bluetooth name of the device is “HC-05” and default PIN (password) for connection is either “0000” or “1234”.

Pin Description

Bluetooth serial modules allow all serial enabled devices to communicate with each other using Bluetooth.

It has 6 pins,

01. State: It tells whether the module is connected or not.

02. RXD: Receive data serially (received data will be transmitted wirelessly by Bluetooth module).

03.TXD: Transmit Serial data (wirelessly received data by Bluetooth module transmitted out serially on TXD pin)

04. GND: Ground Pin of the module.

05. VCC: Connect 5 V or 3.3 V to this Pin.

06.EN: It is used to bring Bluetooth module in AT commands mode. If EN pin is set to high, then this module will work in command mode. Otherwise, by default it is in data mode. The default baud rate of HC-05 in command mode is 38400bps and 9600 in data mode.

HC-05 Technical Specifications

  • Operating Voltage: 4V to 6V (Typically +5V)
  • Serial Bluetooth module for Arduino and other microcontrollers
  • Operating Current: 30mA
  • Range: <100m
  • Works with Serial communication (USART) and TTL compatible
  • Follows IEEE 802.15.1 standardized protocol
  • Uses Frequency-Hopping Spread Spectrum (FHSS)
  • Can operate in Master, Slave or Master/Slave mode
  • Can be easily interfaced with Laptop or Mobile phones with Bluetooth
  • Supported baud rate: 9600,19200,38400,57600,115200,230400,460800.


  • -80dBm sensitivity.
  • Up to +4dBm RF transmit power.
  • Low Power 1.8V Operation,1.8 to
  • PIO control.
  • UART interface with programmable
  • baud rate.
  • With an integrated antenna.

Other Bluetooth Modules

HC-04, HC-06, HM-11, ESP32, CSR8645


  • Home Automation

  • Data Logging application

  • Consumer applications

  • Wireless Robots

  • Communicate with Laptop, Desktops and mobile phones

  • Wireless communication between two microcontrollers