A FT-232 USB to serial board is used to program the Arduino. A standard Bluetooth module has to have HID firmware installed. [Dastardly] makes a homemade daughterboard–er, shield–to connect ...

Fortunately for hardware hackers, such an architecture ... cut the trace leading to the Bluetooth interface module and soldered a wire so the switch now pulls an Arduino pin to ground when pressed.

The HID Relay takes the form of a small adapter that has been built using an Arduino Pro Mini, a Bluetooth module, a USB host shield together with a few other components. Check out the video below ...