I wanted to control an Arduino UNO board using my android phones Bluetooth. The UNO board doesn’t have Bluetooth and so requires an external Bluetooth module. I found a small Bluetooth module (BOLUTEK BLK-MD-BC04-B) at digibay.in and purchased it for experimenting.
The BC04 module can be interfaced to your designs using UART. Before pairing with a device, the module enters into a command mode and can be configured using AT commands. Upon pairing with a device the module enters into a communication mode.
Documentation of the module:
BLK-MD-BC04-B Bluetooth Module Specification
BOLUTEK BLK-MD-BC04-B Bluetooth Module AT Commands
Testing the BC04 Bluetooth module:
Since I bought only one module I wanted to be extra careful, and so built a PCB for the module. The design is just an extension of the Application Circuit Diagram from the module specification file.