Hi,
I bought on ebay a HC-05 module and it has 6 pins (VCC, GND, TXD, RXD, KEY and LED). It says that works with 3.3V but can take 4,5~6V from input. How can I be sure what is the voltage to connect to the VCC? And can I directly connect a TXD and RXD from the board to the module or do I need to lower the value to 3.3V?
José Coelho
I don't have such module myself, but if you start with the lower voltage you are on the safe side: connect to the Arduino 3.3V pin and you should be good.
For RX and TX and the other pins it's not unusual to have the other pins to be 5V tolerant on those boards, like for the nRF24 boards.
Consider that if you connect the HC-05 to your Arduino TX/RX pins you cannot use the Arduino IDE serial monitor or any other serial connection to your board as that will clash with the Bluetooth module: either use a SoftSerial using other two pins (search in the Arduino libraries) or don't open a serial connection to the board while connected to HC-05.
Have fun!
Hi again, I decided to try it at default 5V and without any resistor between TX-RX and RX-TX and it worked just fine. I might say that the module has some capacity to lower the voltage.