• HC-05 Bluetooth Module is a low-cost, easy-to-operate & small-sized module used for wireless communication in the Bluetooth spectrum.

• It supports Serial Port Protocol (SPP), which helps in sending/receiving data to/from a microcontroller (i.e. Arduino UNO).

• Its default baud rate is 9600 for data communication and 38400 for command mode communication.

• Its operating frequency is 2.4 GHz ISM Band.

• HC05 uses CSR Bluecore 04-External single-chip Bluetooth system with CMOS technology.

• This module follows the IEEE (Institute of Electrical and Electronics Engineers) 802.15.1 standard protocol.

• Dimensions of HC-05 are 12.7mmx27mm.

• Its operating voltage is 5V. But data Tx/Rx levels at 3.3v. Use level shifter at Rx

• It sends and receives data by UART, which is also used for setting the baud rate.

• HC05 can operate in master/slave mode and thus multiple slave nodes can be controlled using a single master node (called mesh networking).

• HC-05 supports "AT commands", controlled by TX (transmission) and RX (receiver) pinouts.

LED on module tells about different states of Bluetooth module:

• If it's blinking once in two seconds, it has received a command.

• If it's blinking continuously, means the module is waiting for input data.

• If it's blinking twice in one second, means it's connected properly.