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I am using two Bluetooth dongles for an Arduino project of mine. I am only sending a single int over the connection so it does not need to have a high baud rate.

If I use a baud rate of 1200 will I be able to have more range than if I were to use something such as 115200?

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In my experience, radio modules usually have 2 different baud rates:

  • UART baud rate is the baud rate for communicating to microcontroller on the board. Usually, it's adjustable.
  • Over-the-air baud rate is the baud rate for communicating via Bluetooth. It's usually fixed.

I've searched through the user manual and datasheet for RN-41, which is the Bluetooth module inside the dongle. I didn't find any indication that over-the-air baud rate is adjustable in this module.

So, I doubt that you will get more range if you configure the baud rate down to 1200.

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Marginally or not. The serial protocol is only a logical abstraction layer on top of the Bluetooth protocol. The Bluetooth signaling sets up an over the air 'tube' that you can route your data through, independent of what sort of data it is. Data put into it at one end, will come out at the other end. If this 'tube' cannot be set up, then no content is transmitted; if the 'tube' can be set up, then data can be sent through it without any problems.

At a certain point you may get loss of data due to the 'tube' disconnecting/reconnecting, and of course the number of bits you loose at different baudrates will vary. This is not so much to do with pulse width of the data bits, but by the number of packets that are lost in transit.

UART data is not being sent as a serial bit train, but it is encapsulated in packets that containd data and original baud rate. The Bluetooth transceivers decode the original serial bitstrean and encode it into datapackets, the other side reversing it. All being transparent to the user.

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    \$\begingroup\$ A possible interpretation is that the micro-to-module baud rate may not matter, but the reasons why the baud rate could be low would perhaps allow building a lot of redundancy into the data sent, which might help in marginal connection situations. \$\endgroup\$ – Chris Stratton Aug 16 '12 at 19:50
  • \$\begingroup\$ I like to run TCP/IP over my serial connections, so I don't have to worry about almost anything. It does require a decent microcontroller though, but an Arduino Mega 1280 runs serial IP easily \$\endgroup\$ – jippie Aug 16 '12 at 19:52
  • \$\begingroup\$ @jippie Did you roll you own library for serial IP? Did you find an existing one on the web? After reading your comment, I've tried to find one on the web. No luck yet. \$\endgroup\$ – Nick Alexeev Aug 17 '12 at 22:54
  • \$\begingroup\$ En existing one: arduino.cc/playground/Code/SerialIP It may very well be overkill for a lot of applications, but is does make communicating robust and easy to monitor (you can ping the Arduino for connectivity testing). \$\endgroup\$ – jippie Aug 18 '12 at 12:53
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As others have said, the serial communication rate is not necessarily related to the over-the-air rate. But in general, you might expect the opposite -- a faster over the air data transmission rate might have an increased range, because there is less time that your signal can be negatively affected by changing atmospheric configurations, changing environmental geometry, other radio signal interference, etc.

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    \$\begingroup\$ Some radio modules which allow control of the data rate will vary the input filtering of the radio signal according to the data rate selected. Using a lower data rate will allow modules to filter out more noise, increasing the useful range. In some environments with frequent bursts of noise, it's possible that faster communications may be more reliable than slower communications because the chronologically-shorter transmissions present a "smaller target" for a noise burst to hit, but range is often limited more by the presence of semi-continuous noise than by noise bursts. \$\endgroup\$ – supercat Aug 16 '12 at 22:42

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