HT Bluetooth Master / Slave

HobbyTronics HT Bluetooth Master / Slave
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Manufacturer: HobbyTronics
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HT Bluetooth Master

This is a great little board containing an EGBT-045MS Bluetooth Module, voltage regulation, logic level conversion and LED activity indicators.

These modems work as a serial (RX/TX) connection, and are a great wireless replacement for serial cables.

The HT Bluetooth Module has the same pin out as the FTDI Basic 5V, FTDI Basic 3.3V, Bluetooth Mate Silver and can plug directly into Arduino Pro, Pro Mini 5V, Pro Mini 3.3V boards.

The EGBT-046S Bluetooth Module is a generic Bluetooth device loaded with SPP firmware for UART wireless cable replacement functions. This version of the board can act as a MASTER or SLAVE device. 


  • Radio Chip: CSR BC417
  • Memory: External 8Mbit Flash
  • Output Power: -4 to +6dbm Class 2
  • Range: Up to around 60 feet (20 m)
  • Sensitivity: -80dbm Typical
  • Bit Rate: EDR, up to 3Mbps
  • Interface: UART
  • Antenna: Built-in
  • Voltage: 3.3 to 5VDC
  • Current: 40mA max
  • Firmware: HC05

The default configuration is:

  • Baud Rate: 38400 bps
  • Data : 8 bits
  • Stop Bits: 1 bit
  • Parity : None
  • Handshake: None
  • Passkey: 1234

Bluetooth Board Dimensions (including bluetooth module)

  • Width: 41mm
  • Height: 21mm

Command Mode / Data Mode

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.

The default mode is DATA Mode.

There are two ways to get into Command Mode

1. Connect the CMD pin high before applying power to the module.

This will put the module into command mode at 38400 baud. This is useful when you dont know the baud rate the module is set to.

2. Apply power to the module then pull the CMD pin high.

This will enter command mode at the currently configured baud rate. This is useful if you want to send AT commands from say a microcontroller as the CMD pin can be controlled from one of the microcontroller pins.

Commands are sent to the module in UPPERCASE and are terminated with a CR/LF pair

Command Mode Commands

Apart from the commands described below for configuring master/slave operation, the following useful commands are available.

AT AT Test command. Should respond with OK
AT+VERSION? Get the firmware version
AT+UART=9600,0,0 Set baud rate to 9600

Bluetooth Master Mode

To configure the module as Bluetooth Master and to pair with another bluetooth module follow these steps. Firstly we need to put the module into command mode as above by pulling the CMD pin high.

[Checkout the video at the bottom of the page which goes through the steps so you can see what is happening.]

Follow these steps in order.

AT+ORGL Reset to defaults
AT+RMAAD Clear any paired devices
AT+ROLE=1 Set mode to Master
AT+RESET After changing role, reset is required
AT+CMODE=0 Allow connection to any address
AT+INQM=0,5,5 Inquire mode - Standard, stop after 5 devices found or after 5 seconds
AT+PSWD=1234 Set PIN. Should be same as slave device
AT+INIT Start Serial Port Profile (SPP)
If Error(17) returned - ignore as profile already loaded
AT+INQ Start searching for devices
A list of devices found will be displayed, one of which is the slave module. The format of the output is


The address of the module is what we need and is in the format


We need to replace the colons with comma's when we use the address with the following commands.

If you get more than one device listed and don't know which one is the slave module, you can query the module for it's name using

AT+RNAME? <address>

e.g. (don't forget to change the colons to commas)

AT+RNAME? 0123,4,567890

Once we are happy we have the correct slave address, we need to pair with it, so carry on with the next set of commands.

AT+PAIR=<address>,<timeout> The timeout is in seconds and if you need to type in the pin on the slave device you need to give enough time to do this.
AT+BIND=<address> Set bind address to the slave address
AT+CMODE=1 Allow master to ONLY connect to bound address (slave). This allows the master to automatically connect to the slave when switched on
AT+LINK=<address> Connect to slave. Blue led on board should light up.

Slave Mode

The bluetooth module can also act as a slave. There are fewer commands to set this up.

AT+ORGL Reset to defaults
AT+RMAAD Clear any paired devices
AT+ROLE=0 Set mode to SLAVE
AT+ADDR Display SLAVE address


In the video we setup the module as a Master and connect it to a slave module.


HC05 AT Command Set


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HT Bluetooth Master / Slave
Click to enlarge
HT Bluetooth Master / Slave
Click to enlarge
HT Bluetooth Master / Slave
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