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Embedded Bluetooth - Serial module?

Discussion in 'Electronic Design' started by John Devereux, Mar 1, 2011.

  1. Hi,

    Any suggestions for a SMT/pcb mount module for a bluetooth-serial
    adapter?

    It's to act as a "slave" device, ideally operating a RS485
    tranceiver. I.e.

    PC -> bluetooth -> Module -> RS485

    There seem to be too many manufacturers I have never heard of...

    Qty ~100, initially, would also like it to still be available in 6
    months time.

    Thanks,
     
  2. I'd look for the LairdTech modules. (formerly Ezurio, more formerly TDK).
    I'm using the BISM2 modules for years now with good success. Configured
    properly, they operate as a cable replacement for a serial line. I can help
    you with the proper configuration for that.

    Meindert
     
  3. Hi Meindert,

    Thanks for the recommendation, they look good.

    A quick scan indicates that they need a wired host to configure them
    before use, is that right? I.e. you can't configure them by pins or over
    bluetooth. (But this would not necessarily rule them out for me).

    Or is the configuration non-volatile so it can be done once during
    production. Is this practical for a RS485 node? What we want is to be
    able to send out a bluetooth "box" with our own cabling to connect to
    our RS485 instrument (which may have no UI).
     
  4. hamilton

    hamilton Guest

    So your not going to test this box you send out to customers ??

    Configuration of any BlueTooth module has default and custom settings.

    Just use the defaults.

    hamilton
     
  5. Of course we will test it. The question is whether we have to add a
    separate wired interface to it just so we, or the customer, can
    configure the bluetooth part.
    As I said a quick scan of the manual indicates that the defaults do
    nothing. I.e it looks like the device does not act as a bluetooth node
    at all by default. But if the configuration is non-volatile we can
    probably configure it during test, so that might be OK. But can the
    customer pair with it without a UI? Yes I am being lazy by not going
    through all the documentation to answer these points but it seems like
    Meindart has done it all already so might be able to give me some more
    pointers.
     
  6. No of course not :)

    Hardly anything does AIUI, unless you are willing to except a lossy
    compression over the link.
    That I don't know.
     
  7. Hi John,
    The configuration is stored in non-volatile memory and done by modem-style
    AT commands over the serial port. Once enabled through the serial port, the
    module can also be configured over the air. Switching the DSR line switches
    the module from command to data mode (or and escape sequence which lowers
    the data throughput).
    We configure them during production.
    One caveat: don't use any speeds over 57600 baud without flow control to the
    module (CTS/RTS). I have seen some data loss at 115200 but I am not quite
    sure if it was the module, this test ran on an Mac, running a windows app in
    Parallels (virtual machine). But on 57600 the module will keep up easily.

    I'm not sure if the module could drive the direction control signals of your
    RS-485 chip all by itself. You might need a small timer for that, triggered
    by the TxD pin.

    Meindert
     
  8. OK, thanks Meindart. In particular I was thinking about the user being
    able to pair with the device, since I don't know much about the
    process. As long as the parameters are non-volatile I think we can
    preset everything else ourselves.
    OK, thanks for the tip.
    OK, and thanks again.
     
  9. Jon Kirwan

    Jon Kirwan Guest

    Claims 300kb here:

    http://www.newark.com/jsp/search/productdetail.jsp?SKU=23T4541&CMP=AFC-GB100000001

    Hopefully Laird Tech tests them against their spec.

    Hmm. Close to US$50 each.

    Jon
     
  10. Yes, that is correct. But you still risk internal buffer overflows if you
    don't use flow control. That's what they say in the datasheet too.
    And again: I tested this on a virtual windows machine on a Mac. I have seen
    similar problems with this setup using UDP over one of the network
    interfaces. On a real windows machine, I can dump data as fast as I can to
    my device while on this virtual setup only 5 of the 50 UDP frames I sent
    came across to my device.

    Meindert
     
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