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• HC-06 Bluetooth Serial Module Evaluation

  Rene • 04/20/2017 at 11:55 • 0 comments

  I've had a couple of these modules for a while, but never got around to testing them. There seem to be even cheaper ones available now! If they work as expected, they would be a useful interface (USB alternative) from the ModAir hardware to a tablet / phone / PC.

  I found this datasheet to be the most complete and accurate. Reliable documentation seems to be scarce for most of these cheap Chinese modules.

  I soldered up the 4 wires and added the status LED before heat-shrinking it all together. A FT232R based USB-to-Serial converter is used on the other end.

  When powering up the module, the status LED flashes and the device configuration can be accessed from the serial port side via AT commands. Once a Bluetooth device (in this case my laptop) is connected and the virtual serial port is opened (I used Realterm), the LED stops flashing and remains ON. The AT commands stop working and the link now becomes a straight-through data link.

  Changing the baud rate and device name was straightforward as listed in the datasheet. I changed the baud rate to 921600 bps on both ends and used Tera Term since the file send function in Realterm peaks out at 4800 CPS.

  When from the BT side, Tera Term shows a speed of 22.5 KB/s and all bytes were received correctly on the FT232R side. File size was around 5 MB.
  

  When sending the same file from the FT232R side, Tera Term reports a speed of more than 98 KB/s (theoretical max of 921600 bps == 92160 bytes/sec == 90 KB/s ??), but only around 22% of those are received on the BT side.

  In hardware loopback (TxD to RxD wire):

  • FT232R sustains around 68 KB/s
  • Bluetooth module sustains around 10.8 KB/s

  Seems like these modules are only good for a half duplex data rate of around 20 KB/s, or a full duplex rate of 10 KB/s. Maybe some optimal burst sizes would achieve a higher rate?

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