This is a master and slave in one module, switch by using AT commands.

This module also includes the base board, not only the core board, most functions are pre-set, so only the serial port communication is available but it’s more easy to use.

Communication compatible with other similar Bluetooth serial module: LC-05, HC-05


  • Based on bluetooth module BC04-B.
  • Use CSR popular buletooth chip, bluetooth V2.0 Protocol standard.
  • Serial port operation voltage 3.3V
  • Customize by AT commands for: baudrate, memory mode, module name, master/slave
  • Baud rate set at 9600, customization is possible.
  • Operation current, pairing at 30MA, after pairing is 8 MA during communication
  • sleep mode current: no sleep mode
  • Widely use for wireless data communication such as GPS navigation device, remote data collection, PDA devices
  • Also can pair and communicate with laptop, laptop bluetooth adapter, PDA devices
  • Be aware default setting of the product is slave mode, communication only available between master and slave mode, but not master and master, or slave and slave mode.
  • Board silk pring RXD means you need to the connect the RXD port of another device, and same for TXD port.
  • R2 version add software and hardware master/slave mode select, default is software on. To use hardware select, need cut off connection on software ON with middle pin first.
  • Each purchase if for one piece only.

Setup Mode:

  • Bottom jumper set hardware / software method for slave / master mode, Default setup for hardware method.
  • Top jumper set for slave / master mode.
  • If you prefer to use software method by AT commands to change slave / mater mode, cut the bottom jumper connection (GND – middle pin), then re-connect to top by solder (VCC-middle pin).


Additional information

Weight 0.01 kg

8 reviews for BC-04BK Bluetooth Serial Module BT Master Slave

  1. 1 out of 5


    The description says it can go into master, however whenever i set role to 1 (master) and try run the master commands it gives error 303, which according to the documentation means “it needs to be in lord mode” which I am assuming is master mode. it always resets to slave mode after reset. Slave mode works fine though I bought these specifically for master mode.

  2. 1 out of 5


    I think i found the problem. Pin 4 is supposed to be set to HIGH for software master/slave to work, instead it is wired to low.
    So by default this module will not work.

  3. 1 out of 5


    Ps, error code is 302, not 303

  4. 3 out of 5


    Raising pin 28 on startup puts it in master mode, had to solder a connector to the board it self to do this, not ideal

  5. 3 out of 5

    Chao (store manager)

    Hi, yes indeed, this is a problem, will fix this and contact you for details. Thanks for point this out.

  6. 5 out of 5


    Soldering pin 12 (the 3.3v) to pin 27 (the HW/SW role select switch) fixed it. It now works with software role select.

  7. 1 out of 5


    “Key” button is not working. I can’t go into AT command mode. I checked the connectivity of the button labelled as “Key”, one pin of that button is connected to 3.3v but I can’t find any connection to the other pin with the pins of the main board.

  8. 3 out of 5

    Chao (store manager)

    Key button is for clean pairing configuration. Connected to pin 5 on right, from bottom to top. Please double check.

    When not pairing, you can use AT commands, when paired you can not use anymore.

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