What is HC05 bluetooth module and how it works | Connection and coding | Upm Tech

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Introduction

HC-05 Bluetooth Module
HC‐05 module is an easy to use Bluetooth SPP (Serial Port Protocol) module,designed for transparent wireless serial connection setup.The HC-05 Bluetooth Module can be used in a Master or Slave configuration, making it a great solution for wireless communication.This serial port bluetooth module is fully qualified Bluetooth V2.0+EDR (Enhanced Data Rate) 3Mbps Modulation with complete 2.4GHz radio transceiver and baseband. It uses CSR Bluecore 04‐External single chip Rluetooth system with CMOS technology and with AFH (Adaptive Frequency Hopping Feature).

Bluetooth Module HC-05
The Bluetooth module HC-05 is a MASTER/SLAVE module.By default the factory setting is SLAVE.The Role of the module (Master or Slave) can be configured only by AT COMMANDS.The slave modules cannot initiate a connection to another Bluetooth device, but can accept connections.Master module can initiate a connection to other devices.The user can use it simply for a serial port replacement to establish connection between MCU and GPS, PC to your embedded project, etc.Just go through the datasheet for more details File:Datasheet.pdf

Hardware Features
Typical ‐80dBm sensitivity.
Up to +4dBm RF transmit power.
3.3 to 5 V I/O.
PIO(Programmable Input/Output) control.
UART interface with programmable baud rate.
With integrated antenna.
With edge connector.
Software Features
Slave default Baud rate: 9600, Data bits:8, Stop bit:1,Parity:No parity.
Auto‐connect to the last device on power as default.
Permit pairing device to connect as default.
Auto‐pairing PINCODE:”1234” as default.
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Pin Description
The HC-05 Bluetooth Module has 6pins. They are as follows:

ENABLE:
When enable is pulled LOW, the module is disabled which means the module will not turn on and it fails to communicate.When enable is left open or connected to 3.3V, the module is enabled i.e the module remains on and communication also takes place.
Vcc:
Supply Voltage 3.3V to 5V
GND:
Ground pin
TXD & RXD:
These two pins acts as an UART interface for communication
STATE:
It acts as a status indicator.When the module is not connected to / paired with any other bluetooth device,signal goes Low.At this low state,the led flashes continuously which denotes that the module is not paired with other device.When this module is connected to/paired with any other bluetooth device,the signal goes High.At this high state,the led blinks with a constant delay say for example 2s delay which indicates that the module is paired.
BUTTON SWITCH:
This is used to switch the module into AT command mode.To enable AT command mode,press the button switch for a second.With the help of AT commands,the user can change the parameters of this module but only when the module is not paired with any other BT device.If the module is connected to any other bluetooth device, it starts to communicate with that device and fails to work in AT command mode.This video tells you how you can control LED or any other stuff with the help of an Arduino board, a bluetooth module/sensor & an Android/smartphone !