This is the popular Bluetooth module, HC05 which can be configured as master or slave.

• Master Bluetooth will be able to search for other Bluetooth devices and initiate connection.
• Slave Bluetooth cannot search for other Bluetooth devices and can wait for master to initiate connection and accept the connection.

It's very easy to add wireless serial connectivity for your device with this module because it comes with UART interface. Examples project for Arduino and other boards are widely available. Once it is paired with other Bluetooth device it works like normal UART to exchange data. We called this transparent mode.

This module have build in 3.3V voltage regulator and helps to breakout the important pins (STATE, RXD, TXD, GND, VCC and EN). Based on CSR BC4 chip, Bluetooth V2.0 + EDR. It is default loaded with SPP (Serial Port Profile) which become UART when it is connected via Bluetooth link. And there is a push button on HC-05 to set it into AT mode. Do check the video on how to use the button.

Features:

• Bases at CSR BC04 Bluetooth technology.
• With build-in 2.4GHz PCB antenna
• It’s at the Bluetooth class 2 power level.
• Range test: 10 meters
• Operating voltage: 3.3V to 6V DC
• Operating current in pairing is in the range of 30~40mA.
• Operating current in communication is 8mA.
• Interface via UART:
  • Default baudrate in Normal mode: 9600 bps
  • Default baudrate in AT Command mode: 38400 bps
• Operating temperature range: -25 °C - +75°C
• Dimensions 27mm×13mm×2.2mm

Packing List:

• 1 x HC05 Bluetooth module

Documents:

• HC05 datasheet
• AT Mode Sample code - Arduino