Adding Bluetooth to the MSP430 Launchpad

The National Semiconductor LMX9838 Bluetooth Serial Port module is a fully integrated Bluetooth 2.0 baseband controller, 2.4 GHz radio, crystal, antenna, LDO and discreets; combined to form a complete small form factor Bluetooth (BT) node[1] . I made a board (not my best soldering job) to connect an LMX9838 to a Launchpad and test it out. The circuit is really simple, the module needs a couple of resistor to set the baud rate (9600) and 3.3 volt, that it’s!


The basic circuit (just sending data) use  three wires; VCC, GND and the TX->RX connection.

Adding Bluetooth to the MSP430 Launchpad

After powering up the module is recognized by the PC as a Bluetooth Serial Port Device and the installation was pretty straight forward.Sin5

I programed the Launchpad (LP) using Energia but I wasn´t receiving the right data using the BT module. The circuit seemed to be fine so I tried with a simpler program that just send “hello world” every time I press the S2 switch. This is what I got:


D is an MSP430G2452 using the LP serial interface to send the message, C is the same MCU with the BT module. The data was there but for some reason the BT module wasn’t sending the whole message. Then I changed the MCU and used an MSP430G2553 instead and A shows the LP serial interface and B shows the data received through the BT module.  It seemed like the BT module doesn’t like the software UART implemented in the MSP430G2452 but works fine with the hardware UART in the MSP430G2553. I connected the Open Bench Logic Sniffer to see what’s going on and the signals seemed to be the same with both microcontrollers. I analyzed the data stream with the software and there was a little difference between the signals.

uartsw uarthw

The first image shows that the baud rate using the MSP430G2553 with hardware UART is 9523, pretty close to 9600. The other one is the software UART and the baud rate there is 9090, a 5.31% difference that the BT module seems to not be able to handle.


10 thoughts on “Adding Bluetooth to the MSP430 Launchpad

  1. Thanks, I have lmx9838 and msp430. I will try it, but there are rts, cts, pg6 pins and crystal in the datasheet reference designs, so I am confused. I want to only send and receive data over bluetooth with computer.

    • According to the datasheet:
      RTS-> Not Connected (if not used)
      CTS-> GND (if not used)
      PG6 is there to connect a led to show the LINK status
      and the crystal:
      32K- -> NC (if not used)
      32K+ -> GND (if not used), i didn’t use a crystal

  2. Hello ssihla
    When you said “After powering up the module is recognized by the PC as a Bluetooth Serial Port Device and the installation was pretty straight forward”, I am guessing that you are using 2 PCs- First PC connected to MSP launchpad to write and download the program and Second PC to recognize the Bluetooth. Is that right? Is the realterm software installed on PC2?
    Thank you.

    • Nop, just one PC. The BT module doesn’t need any configuration (except for the resistors to set the Baudrate). I programmed the MSP430 to send data through UART, but disconnected the jumpers in the LP Board, so instead of using the USB/Serial Port y used the BT module.

      • Hi. How did you do that? I´ve tried here i could not make it. My windows7 always recognize the lauchpad as a lauchpad itself (instead of the BT module), even if a remove the TX, RX Emulator Jumpers. Could you tell me how you wrote the code?
        Thx a lot.

      • The launchpad will not be recognized as a BT module. Once you power on the BT you have to add a new BT device in win7, you’ll see the module there.

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