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  • 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.





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