Bluetooth module with a bottom plate, this module is used HM-10 module.
5V power supply or 3.3V power supply Serial port power supply voltage and the same level
Built-in level conversion.
RX, Bluetooth module serial port receiver and MCU TXD connection.
TX, Bluetooth module serial port transmitter and MCU RXD connection.

Product Introduction:

1.Input Voltage:3.3V/5V 
2.Built-In Level Switch Function: 
If use 5.0V MCU to make communications with bluetooth module,5.0V power port supply power,RX TX logic level 5V 
If use 3.3V MCU to make communications with bluetooth module,3.3V power port supply power,RX TX logic level 3.3V 
3.RX:bluetooth module serial receiving port connect with MCU TXD 
4.TX:bluetooth module serial transmitting port connect with MCU RXD 
5.GND:ground port power negative 6.3.3V:power port 3.3V power 7.5V:power port 5V power