UART
https://github.com/jdunmire/HC05
http://wiki.iteadstudio.com/Serial_Port_Bluetooth_Module_(Master/Slave)_:_HC-05
https://arduino-info.wikispaces.com/BlueToothCommandUtility?responseToken=06a422624d3118e9d6b678cfe47c8a449
3 €
Aliexpress