# Bluetooth HC-05 AT Commands

I'm attempting to put an HC-05 module into command mode in order to change the PIN and default baud rate etc. According to the datasheet, PIO11 needs to be high to do this, so I connect it to 3.3v, remove power and power it back up.

Using an FT232 interface and a level converter, I send the AT command to it via Putty. I can observe the command on the RX pin of the HC-05 module but I don't see anything come back. I've tried various combinations of baud rates and flow control settings.

For the record, I can pair with the module and receive data sent to it in my Putty window via the FT232/level converter.

I got there in the end with this. Bear in mind the following conditions when trying to send AT commands to the HC-05:

• The default baud rate on my module was 9600, not 38400 as described in certain places
• If you make PIO11 (key) high (3.3v) while the module is on, it will enter AT command mode but will retain the default baud rate
• If you power the module up with PIO11 high, it will enter AT command mode but the baud rate will be set to 38400
• All AT commands must end with Carriage Return and Line Feed (\r\n)

The key bit for me was sending AT commands CR & LF enabled on transmit.

For going into command mode Use a TTL to USB converter.

To connect this converter module to the Bluetooth module, just follow the following wiring

    ***** VCC Bluetooth to VCC Converter
*** GND Bluetooth to GND Converter
*** TX Bluetooth to RX Converter
*** Bluetooth RX to TX Converter
that is all!**


To switch to command mode, disconnect power (pull from USB) before reconnecting, power PIO11 needs to be high  In this case, connect the converter to the USB port to turn it on. Now if you look at the LED it's blinking slower than before. So drop PIO11 Welcome to Command mode and start sending commands.

• My module wasn't mounted on a PCB with those pin outs. It was just the (34 pin) surface mount part I was trying to use. Mar 3 '20 at 8:23

I have been purchased modules with KEY button on the interface board. So the only thing I need is to hold it pressed during connecting power.

In my case:

• i used USB-TTL converter based on PL2303 chip,
• command mode always use speed 38400,
• to check the values there is no need to append question mark at the end,
• text values (pin, name) must be quoted,
• Arduino IDE's serial monitor works fine for me.