If you want to change some of the settings of your HC-05 Bluetooth module, like baud rate, password or the name of the Bluetooth module, you can do it easy and fast with your Arduino.
There are different HC-05 modules on the market, but it should work with all of them. On the picture below you can see a bare HC-05 module, 5V tolerant HC-05 module and 6V tolerant HC-05 module with a button. I prefer the last one, as the button makes the changing of the settings even easier.
To change any settings of the module, it should be in the so called “AT Mode”. How to put the Bluetooth module in AT Mode: The “Key Pin” of the module should be set to “High”. This means we should apply voltage to this pin at the same time we power the module. On the last module, the button does this job. It should be pressed when powering the module with 5V. On the module without button, we need to supply 3.3V to the “Key Pin” when powering on.
Here is an example how to connect the module to the Arduino Nano v3. Note that there should be an jumper on GND and RST pin. By doing this, the Arduino will only act as a simple FTDI adapter.
First connect the Arduino to the PC over USB. Then connect the cables in the following way:
TX Bluetooth –> TX Arduino
RX Bluetooth –> RX Arduino
GND Bluetooth –> GND Arduino
… and at last the 5V Bluetooth to 5V Arduino by keeping the button of the Bluetooth pressed. Or on the module without button, connect the Key Pin Bluetooth to 3.3V on Arduino.
If the HC-05 is in AT Mode, the red LED will blink at every 2 seconds.
Then start the PuTTY program configure the right COM Port (Check it in the Device Manger) and set the Baud Rate to 38400. This is the baud rate for AT Mode. Then click “Open”.
In the newly opened black window type “AT”, press Enter and you should get “OK” as a result. Note that you want see what you type in the windows… Here some of the commands to change the settings you wish:
|Change baud rate to 57600, 1 stop bit, 0 parity
|Change module name
|Change pairing code
Note: You can use other similar terminal applications such as teraterm, Hyperterminal, Docklight these all were supported by windows. For ubuntu users you can use gtkterm terminal.