The easiest way to configure the HC-05 Bluetooth Module using AT command, is by using a USB to TTL converter.
The HC-05 Bluetooth Module (with factory default baud rate 9600, 8, N, 1 and is set as slave) used:
The USB to TTL Converter used:
Only 4 pins on the HC-05 Bluetooth Module are used with connections to FTDI USB to TTL Converter.
HC-05.VCC - FTDI.VCC
HC-05.GND - FTDI.GND
HC-05.RX - FTDI.RXI
HC-05.TX - FTDI.TXO
To enter the AT mode, follow the procedure listed.
Step 1: Plug the FTDI USB To TTL Converter (with connections to HC-05 Bluetooth Module listed above) to the USB Socket on Computer. The led on the HC-05 Bluetooth Module will flash quickly at about 2Hz.
Step 2: Short the HC-05.VCC and HC-05.KEY pins for a short time (touch and seprate) to set
the HC-05 in AT Mode. The led flash as quickly as ever.
Step 3: Open Arduino IDE Serial Monitor. Set baud rate to 9600 and select "Both NL & CR".
Step 4: Type AT, press "Enter" on keyboard or click "Send" icon on Serial Monitor. The "OK" response should be displayed.
