I'm writing this instructable because I have had nightmares getting this cheap, but well built bluetooth module to work. It was worth the challenge to save myself $50 for a simple SPP serial port (RS232 Emulator) service! I will go over the do's and don'ts I discovered while spending weeks with this board, both hardware and software.
I am assuming you are connecting this module to an Arduino or similar MCU development board.
Next up - The Pins...
Step 1: The Pins
The module has 6 pins labeled on the back, but most modules only have 4 of those populated with pogo pins. KEY & STATE seem to be not required, as KEY is used for flashing the device and STATE simply indicates if the device is awake or not. So that leaves only GND, VCC, TXD, RXD. Not shown is Pin 11 which is the RESET pin, resetting the module when pulled LOW.
Some boards have VCC labeled for working voltages up to ~6 volts. These modules DO NOT like anything except 3.3 volts on the VCC line. Also, some forums claim that the device works fine with 5 volt TTL levels. This is also not true and you should use a level converter to 3.3V on the RXD line. I used two resistors as a simple voltage divider to make the TTL level conversion. One 2.2k ohm resistor to ground, connected to a 1k ohm resistor, to the TXD line on the MCU. Connect the RXD pin in between the two resistors for an output of approx 3.4 volts. This about covers the hardware side of the module. As it turns out, the VCC voltage was one of the last things I tried to have full success with the module.
Next up - The Software...