Problems with serial communication from Arduino to Bluetooth HC-05 I just purchased some HC-05 Bluetooth devices and I have followed the directions to put the devices in AT command mode by holding EN HIGH when the HC-05 powers up.  When I do this the HC-05 goes into the "slow blink" to indicate it is in command mode.  However, when I send it "AT" I get odd characters in the response.

Note that when I type "AT" I get exactly 4 characters back.  They are just not the "OK" characters I expect.  I also verified that the Arduino IDE serial console is sending both NL and CR characters.

BTW, here is the Mel Patrick HC-05 authored setup program I am running:

https://raw.githubusercontent.com/dmccreary/coderdojo-robots/master/src/bluetooth-remote/hc-05-setup/hc-05-setup.ino



It has been suggested that the data from the HC-05 is only going up to 3.3v and that might be the cause of the problem, since the Arduino is looking for a 0-5 volt signal.

I also note that when I remove the TDX line from the HC-05 that no responses come back.  So I suspect that it is getting the "AT" fine through the RTX from the Arduino to the HC-05.  It is just some problem in the return data format.

Is there a simple transistor circuit I can hookup to shift the levels back to 0 to 5 volts from the 0 to 3.3 volts?

I am also using an Arduino Nano if that makes any difference.

Thanks - Dan
If you use software serial for Bluetooth, you need to set the baud rate and the default baud rate of HC-05 is 38400.

You can change this baud to the desired with AT command.