1. BLUETOOTH modules…?

2. HC-05
HC-06
BLE-mini
BLUE-SMiRF

3. Bluetooth module( HC-05)
Bluetooth is a wireless technology standard for exchanging data over short distances (using short-wavelength UHF radio waves in the ISM band from 2.4 to GHz) from fixed and mobile devices, and building personal area networks (PANs). Range is approximately 10 Meters (30 feet).
CLASS -2 (10Meter)
This modules are based on the Cambridge Silicon Radio BC GHz BlueTooth Radio chip. This is a complex chip which uses an external 8 Mbit flash memory.

5. Pin diagram..

6. PIN OUT DETAILS..
KEY: If brought HIGH before power is applied, forces AT Command Setup Mode. LED blinks slowly (2 seconds)
VCC: +5 Power
GND: System / Arduino Ground
TXD: Transmit Serial Data from HC-05 to Arduino Serial Receive. NOTE: 3.3V HIGH level: OK for Arduino
RXD: Receive Serial Data from Arduino Serial Transmit
STATE: Tells if connected or not

7. How does it works..?
It only receives commands sent by android device and according to sends data to Arduino, hc-05 it self is not sending any commands or not sharing clock . This is not AT commands ,in AT commands hc-05 can share clock with other Bluetooth modules and can give commnds to them. Also they can create network with such 10 modules called as Piconet.

8. ADVANTAGES. Mobile phone and a Bluetooth compatible car stereo system
ADVANTAGES.. Mobile phone and a Bluetooth compatible car stereo system. Wireless Mouse ,Keyboard ,Printer. Audio to headphones ,mobile to mobile communicatons.. Used in Automation projects. Used in mobile phones, smart watches.. DISADVANTAGES: Short range.

9. WHAT’S BLUETOOTH …..?
Bluetooth is a global wireless communication standard t hat connects devices together over a certain distance
Dr. Jaap Haartsen, who invented Bluetooth while workin g at Ericsson in the 1990s
How does Bluetooth work? A Bluetooth device uses radio waves(2.4 Ghz) instead of wires or cables to conne ct to a phone or computer    

10. SPECIFICATIONS OF BLUETOOTH…
Range generally 10 metere. But depends on class of Bluetooth.
Sending and receiving data over 2.4Ghz..
Its perfect protocol for shortrange .
Low cost.
Low power(3.3 v)
Easy to use(just pair and share)
Class of bluetooth
Distance
Class 1
100 m
Class 2
10 m
Class 3
10 cm

11. Speed: varies with versions of Bluetooth..
25 Mbits/sec
Bluetooth 4.0
25Mbits/sec
Bluetooth 5.0
50 Mbits/sec