HC-05 Bluetooth Module AT Mode Using FTDI USB To TTL Converter and Arduino Serial Monitor

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.

FT232RL USB To TTL Converter

This is a basic breakout board for the FTDI FT232RL USB to serial IC. The pinout of this board matches the FTDI cable to work with official Arduino and cloned Arduino boards. The major difference with this board is that it brings out the DTR pin as opposed to the RTS pin of the FTDI cable. The DTR pin allows an Arduino target to auto-reset when a new sketch is downloaded. This is a really nice feature to have and allows a sketch to be downloaded without having to hit the reset button. This board will auto reset any Arduino board that has the reset pin brought out to a 6-pin connector.

The pins labeled BLK and GRN correspond to the colored wires (black, brown, red, orange, yellow, green as the sequence of resistor color code from 0 to 5) on the FTDI cable.

You can see serial traffic on the TX and RX LEDs on the board to verify if the board is working.

This board was designed to decrease the cost of Arduino development and increase ease of use.

One of the nice features of this board is a jumper on the top of the board to be configured to either 3.3V or 5V. You can resolder the jumper if you need to switch between 3.3V and 5V.

Justduino = Freeduino/Arduino + Sensor Shield - USB to TTL Converter

Justduino is a simplified Freeduino/Arduino based on Duemilanove with sensor connectors integrated.