I have a requirement to make a BT2.1 adapter, which I have to connect to a balance scale via serial port. The weighing scale transfers weight data to the adapter via serial port. This BT adapter has to pair to any mobile phone. The application running on the BT based mobile phone should display the weight measured on the weighing scale.

Keeping this in mind, can anybody suggest me the profile that i should implement on the BT adapter?

Also, Is anybody aware of a single chip based BT solution which I can use for building the adapter?

I am new to the world of Bluetooth...

  • \$\begingroup\$ I confirm that the HC-05 module works with 230400, but not 460800 \$\endgroup\$
    – user17475
    Jan 2 '13 at 18:38

Sounds like you need to use the SPP (Serial Port Profile)

This basically makes the BT module look like a UART to whatever is connected to it, although internally the BT module deals with things in packets (transparent to the user)

You will need to implement the module as a master service, then anything can request to connect accordingly (modules mentioned below usually come set to master, but can be changed)

For the actual module, there are various well documented on Farnell, Mouser, etc, but pricey (>£10 generally)
For cheaper options that come with next to no documentation there are plenty on eBay to choose from. Luckily I have recently been through the frustrating process of... *rant on* messaging vendors for detail/documentation, getting no reply (apart from "did you buy our module?"), buying a few samples, trying to work out what the AT commands are, searching for/finding documentation elsewhere and attempting to match it with the module, finding out the higher few baud rates advertised don't work and if set to cause the module no longer to respond to AT commands, messaging the vendor with requests for clarification on this matter and getting no reply and much more fun stuff *rant off*

In the end I found out that the HC-05 (not HC-06 as you cannot change master/slave) is a reasonable module and AT commands and pinout documentation can be found for it. I used one like this, though you can get them with a header adapter (e.g. for plugging into breadboard) Just search for "HC-05".

Note that the advertised maximum rate of 1382400 is almost certainly unachievable. I have tested okay at 115200 (I think 230400 works too, but it's around 460800 problems start. IIRC the module worked okay at this speed but I could no longer get any response from AT commands - may not be an issue it you just want to "set and forget")
Note that some have a cmd pin which needs to be driven high to enter AT commands, and some are automatically in this mode when not paired (if you get one with no cmd pin, then it will probably be the latter)

User manual
AT commands
Company Website (use Google Translate and look over to the right under "Download Section")


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