LeaningTech HC-05 Wireless Bluetooth Host Serial Transceiver Module Slave & Master RS232 for Arduino (BC27823) Bluetooth module hc-05 Master and Slave two in one module Use the CSR mainstream Bluetooth chip, Bluetooth V2.0 Protocol standards Module working Voltage 3.3 V Potter default rate of 9600, the user can be set up The Core module size : 28 mm x 15 mm x 2.35 mm