Review on DSD TECH HC-05 Bluetooth Serial Pass-through Module: Seamless Wireless Serial Communication with Arduino Button by Rob Sanchez

The documentation is a little inconsistent, but it worked for me at 3.3v. I'm using the Sparkfun CH340 USB-UART for testing. This outputs 3.3 V at up to 600 mA. The manual says the HC-05 operates at 3.1V to 4.2V and 30mA to 40mA. The Revain and DSD Tech websites, as well as the board itself, state that the 3.6v to 6.0 VI uses two serial ports, one connecting to the CH340's COM port and the other to either one (why two?) Bluetooth COM ports is connected to HC-05. (both on 9600 8N1) and had no communication problems. I got it into AT mode on the first try, using method 2 I held the button down when it was on. I held it for a few more seconds until the light started blinking. I set their Bluetooth Tools software to 38400 (default for Method 2) and selected the CH340 COM port and I was able to change the HC-05 settings.