LeaningTech HC-05 Module Bluetooth Serial Pass-Through Module Wireless Serial Communication with Button for Arduino Bluetooth module HC-05 Master and slave Two in one module Use the CSR BC417 mainstream bluetooth chip, bluetooth V2.0 SPP protocol standards Module working voltage 3.6 V to 6V Default rate of 9600,default pin:1234, the user can be set up.click the button into AT MODE Can be switched via AT commands as master or slave mode , the device can be connected via AT commands specified