Arduino HC-05 HC05 Wireless Bluetooth Serial Port TX RX Module

Features
The HC-05 is based on the EGBT-045MS Bluetooth module. It can operate as either a slave device or a master device. As a slave it can only accept connections. As a master it can initiate a connection.

The EGBT-045MS Bluetooth modules (the smaller daughter board) is a 3.3v device. The HC-05 break out board has a 3.3v regulator that allows an input voltage of 3.6v to 6v but the TX and RX pins are still 3.3v. This means you can use the 5V out from the Arduino to power the boards but you cannot connect the Arduino directly to the HC-05 RX pin.

For the HC-05 RX pin (data in) we need to convert the Arduinos 5V to 3.3v. A simple way to do this is by using a voltage divider made from a couple of resistors. In my case I use a 1K ohm resistor and a 2K ohm resistor.

As a quick guide to the voltage divider; 1K + 2K = 3K. 1K is a third of 3K so it reduces the voltage by a third.
One third of 5V is 1.66 and 5-1.66 = 3.33 which is what we want. Putting the resistors the other way would reduce the voltage by 2 thirds.
For more information on voltage dividers have a look at the Sparkfun tutorial

Since the Arduino will accept 3.3 volts as HIGH you can connect the HC-05 TX pin (data out) directly to the Arduino RX pin (The 5V Arduino takes a voltage of 3V or more as HIGH).

Specification:

Model: HC-05
Input Voltage: DC 5V
Communication Method: Serial Communication
Master and slave mode can be switched
Transmission distance: 20 ~ 30m in free space

Attachment:
HC-05 Bluetooth Module User's Manual v1.0: https://drive.google.com/file/d/0ByfmRaocZIg0S0x0UGdmNC15Z3c/edit?usp=sharing
Arduino Source Code: https://drive.google.com/file/d/0ByfmRaocZIg0bDgxVk5mLUMyMWM/edit?usp=sharing
Mybotic Serial Com Tool: https://drive.google.com/file/d/0ByfmRaocZIg0WkhTTnlXS25ONmc/edit?usp=sharing
Bluetooth Software with Driver (IVT BlueSoleil): https://drive.google.com/file/d/0ByfmRaocZIg0SExqa2JZaTZXUnc/edit?usp=sharing

Related Link
Modify The HC-05 Bluetooth Module Defaults Using AT Commands by techbitar :https://www.instructables.com/id/Modify-The-HC-05-Bluetooth-Module-Defaults-Using-A/#step0