This document describes the bluetooth module included with LEDI. There are two different kinds of modules: HC-05 and HC-06. Contrary to what the model number might suggest, the lower numbered model, HC-05 is the more "advanced" module.

The model HC-05 is both master and slave bluetooth device, whereas HC-06 is slave-only. Both modules have factory setting of 9600 baudrate.

There are two different kinds of modules that look exactly the same:

  • HC-05 Master and Slave module
  • HC-06 Slave-only module

Externally, these modules look identical. Simply from inspection, you cannot tell them apart. As far as the hardware is concerned, both of these modules seem to have identical components. The root of the differences lie in the firmware of these modules.

The module has a lot more accessible pins that what it requires. Many of these PINs are general I/O pins and seem to be controlled from the firmware. Essentially, the differences between the two modules are:

  • Slightly different recommended electrical wiring
  • Default device name (HC-06 is linvor, HC-05 seem varied)
  • Ways of entering AT modes
  • Supported AT commands

Physical Wiring on LEDI

LEDI is compatible with both types of modules – the PCB wiring was designed to accomodate either modules. In addition, a breakout header gives direct access to the bluetooth module.

In essence, the LEDI board can be used as a standalone bluetooth board that can be interfaced from other exteral devices.

Testing Connection from PC Bluetooth

This is tested on Ubuntu. If you have bluetooth in your hardware you can readily do this.

First scan to see if you can detect LEDI:

hcitool scan

And now edit /etc/bluetooth/rfcomm.conf and put in an entry like this:

rfcomm0 {
  # Automatically bind the device at startup
  bind no;

  # Bluetooth address of the device
  device 00:12:07:11:13:60;

  # RFCOMM channel for the connection
  channel 1;

  # Description of the connection
  comment "any description you like";

Once that’s done, run:

sudo rfcomm release rfcomm0 # if already connected
sudo rfcomm bind rfcomm0
sudo rfcomm connect rfcomm0

A PIN request popup window will show. Put in 1234 and you will pair with LEDI. Now, you can use the rfcomm like a serial port device:

sudo minicom -D /dev/rfcomm0 -b 9600 -8

Changing The Module Configuration

In most cases, changing configuration parameters on HC-05/06 is not required. However, there are several useful things you can do with config change:

  • Increase the baud rate, thereby making UART communication faster
  • Change the bluetooth module name
  • Change the pairing PIN code
  • Change pairing behavior (HC-05 only)

Setting Up FTDI Adaptor

The module operates at 3.3v. You will need 3.3v USB to serial adaptor (e.g. FTDI breakout) to connect to the BT module.

Learning The AT Commands

The command set is quite different between HC-05 (master,slave) and HC-06 (slave-only).


I’ve tested this on Ubuntu. I used minicom before, but found this awesome terminal program:

Quick list of commands I ran:

# install the prerequisites
sudo apt-get install libqt4-dev
sudo apt-get install libudev-dev
sudo apt-get install libqwt-dev

# install qtserial port
cd $HOME/git
git clone git://
cd qtserialport
sudo make install

# now install qSerialTerm
cd $HOME/git
git clone git://
cd qSerialTerm
sudo make install

Command Set for HC-06 (Slave only device)

HC-06 goes into AT mode only when the module is not paired with any device. It doesn’t need any explicit pull-down on any of the pins.

Here are the supported AT commands for HC-06.

Command Response Comment
AT OK Does nothing!
AT+VERSION OKlinvorV1.5 The firmware version
AT+NAMExyz OKsetname Sets the module name to "xyz"
AT+PIN1234 OKsetPIN Sets the module PIN to 1234
AT+BAUD1 OK1200 Sets the baud rate to 1200
AT+BAUD2 OK2400 Sets the baud rate to 2400
AT+BAUD3 OK4800 Sets the baud rate to 4800
AT+BAUD4 OK9600 Sets the baud rate to 9600
AT+BAUD5 OK19200 Sets the baud rate to 19200
AT+BAUD6 OK38400 Sets the baud rate to 38400
AT+BAUD7 OK57600 Sets the baud rate to 57600
AT+BAUD8 OK115200 Sets the baud rate to 115200
AT+BAUD9 OK230400 Sets the baud rate to 230400
AT+BAUDA OK460800 Sets the baud rate to 460800
AT+BAUDB OK921600 Sets the baud rate to 921600
AT+BAUDC OK1382400 Sets the baud rate to 1382400

Command Set for HC-05 (Slave and Master)

Good Resources

  • This link shows how o communicate against HC-06 module from a PC