Eztronics Corp&reg; Bluetooth Serial Transceiver Module Base Board HC-05 Baseboard For Arduino This module includes key interface and state interface compared with Smart Bluetooth Module Baseboard. The Bluetooth Module Baseboard can be compatible with master mode,slave mode and both master-slave mode. Works for Bluetooth TTL transceiver module which allows your target device to both send or receive the TTL data. The key interface on the baseboard is the master mode button and can be controlled by high level from external MCU, then this module will search again automatically. This module power supply input is 3.6~6V, Please be careful that it should be not more than 7V.