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Bluetooth Module


Bluetooth module is a wireless technology standard for exchanging data over short distances from fixed and mobile devices, and building personal area networks (PANs). The range is approximately 10 meters. In this post we will mainly talk about the HC series of bluetooth modules.

Bluetooth serial module is used for converting serial port to Bluetooth. These modules have two modes: master and slaver device. The device named after even number is defined to as slave. But the device named after odd number, users can set the work mode master or slave of the device by AT commands.

There are basically 2 modules which are commonly used: HC 05 and HC 06

Pinout and Entering AT Mode


  • HC-05 is a more capable module that can be set to be either Master or Slave.
  • HC-06 is a Slave only device. (It looks physically just like the HC-05).
  • These modules run on 3.3V power with 3.3V signal levels, They have no pins and usually solder to a larger board.
  • The module has two modes of operation, Command Mode where we can send AT commands to it and Data Mode where it transmits and receives data to another bluetooth module.


Bluetooth modules are used to transfer and receive files within a specific range.


Project for Reference:


After code is finished, Download the app “S2 terminal for Bluetooth” on your smartphone Then, pair your phone with your Arduino(Bluetooth module).

Go to the app, and again pair up your phone to HC-05 via the app.

Next, upload the given code below and you are good to go!

So now, you can type in from your phone( in the app basically) and see the result on your monitor and vice versa. ( observe the results by opening Serial Monitor on your desktop)