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I see a lot of baud rates in the AT Command documentation for the HC05 however I am not sure what is the fastest that can work between the Arduino controlled embedded system and the Android phone. I also do not know of a way to change the baud rate of the Bluetooth communication in software. I am writing the application in Java with Android Studio IDE.

I read the documentation for HC05 and realize that it only operates with one Bluetooth profile. i.e the Serial Port Profile. The documentation says that this profile offers a maximum data-rate of 128000 bits/sec. However, the HC05 has a max baud rate option of 1382400 bits/sec. Why would this option be there if it is not possible to use? Can you please explain what I am missing and point me into the direction of some useful information? Thank you.

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The HC-05 may only have implemented baud rates up to 1382400, even though the protocol is spec'd for up to 128000.

If you're using Software Serial to talk to the HC-05 from an Uno, 9600 baud is about as fast as SoftwareSerial can keep up with incoming bytes (I've heard from some people that 19200 will work).

If you're using one of the UARTs on a Mega, you may be able to use the full rate implemented by the HC-05. An experiment would be in order...

Update:

I did an experiment and found out that the maximum baud rate achievable between the HC05 (communicated with by SoftwareSerial on Arduino Nano) and the Android device is 115200.

I would guess you were transmitting from the Arduino? I've been able to transmit that fast with SoftwareSerial but its receiving ability is more limited. (This has enabled me to, f/ex, set an HC-05 or an ESP8266 to a slower baud-rate than it shipped with, by blindly transmitting an appropriate 'AT' command at the higher speed, then testing it at my intended speed to see if the command worked).

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  • I did an experiment and found out that the maximum baud rate achievable between the HC05 (communicated with by SoftwareSerial on Arduino Nano) and the Android device is 115200. Any baud rate higher than this did not work for neither HC05 - HC05 nor HC05 - Android. Also, I could not find a way in the Bluetooth Documentation (developer.android.com/reference/android/bluetooth/…) to change the baud rate used on the Android device with Bluetooth SPP. It was as if the device automatically adjusted to the baud rates I configured on the HC05. i.e. 9600 - 115200.
    – Alick Campbell
    Mar 7, 2021 at 7:20
  • Seems logical, that Android will change the baudrate to be matched. The communication from HC-05 to Android is only a virtual serial interface. Baudrate doesn't have much meaning for it. Only the real UART interface between HC-05 and Arduino really needs a baudrate
    – chrisl
    Mar 7, 2021 at 20:45

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