Fail: My old HC-05 Bluetooth module was an HC-06 and it only took me a week to figure it out.

Sometimes you make bad assumptions and they lead you into the alley for a week.  Then you figure it out and get back on the path to getting stuff done.

I spent a week trying to reconfigure my Bluetooth HC-05 module to a higher data rate. I tried the key pin.  Then I tried strapping the mode switch pin to 3.3 volts.  Nothing worked.  My devices were 8 years old so I assumed the missing buttons on my devices were just a versioning thing

My HC-06 Devices JY-MCU

I was just stuck with 9600 bps which is not cool because causes its own issues https://joe.blog.freemansoft.com/2023/01/replicating-micropython-repl-across-hc.html

I did notice something weird it always responded to the AT command when connected to a terminal prompt.  It just didn't respond as expected to the AT commands.  I couldn't type any of the expected commands.

HC-06 Bluetooth board JY-MCU

Eventually, I ran across this instructable that said that the board with my markings was probably actually an HC-06 which was always in command mode. This was originally an HC-05 article that had HC-06 content added later.  That mix of content was enough to recognize the issue.

  • https://www.instructables.com/AT-command-mode-of-HC-05-Bluetooth-module/#:~:text=For%20HC05%3A%20Type%20%22AT%22,name%2C%20type%20AT%2BNAME.
Yes, there are a bunch of pictures about the differences between the two devices but there were so many variations over enough years that they weren't convincing. Or I had a preconceived notion I wouldn't give up.

Communicating with the HC-06

The HC-06 is always in AT command mode.  You don't strap one of the pins to switch from data to command. 

The HC-06 AT command mode expects the entire command to be entered within 1 second.  This is part of the reason only bare AT was accepted. I took longer than a second to enter the command.  The Bluetooth adapter started responding as an HC-06 when I pasted the commands into the window instead of typing.  Note that you never need a return character.  Just paste the whole line as is with no extra spaces or returns.

  • AT
    • Replied: OK
  • AT+NAME
    • Replied: setname
  • AT+VERSION
    • Replied: linvorV1.5
  • AT+NAMEMOD2
    • Replied: <i don't remember>
    • Changes the name to MOD2
  • AT+BAUD8
    • Replied: OK115200
    • Changes the device RX/TX rate to 115100

Revision History

Created 2023 01

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