Last post show a "Android communicate with Arduino + HC-06 Bluetooth Module". Alternatively, the HC-06 can connect to PC via a FTDI USB-to-Serial adapter, such that Android can talk to PC by Bluetooth.
This video show how to:
Android side, refer to last post "Android communicate with Arduino + HC-06 Bluetooth Module", with source code and APK.
In my setup, both FT232RL (FTDI USB-to-Serial adapter) and HC-06 (Bluetooth Module) operate on 3.3V.
HC-06 VCC - FT232RL VCC *make sure both devices work on the same voltage.
HC-06 GND - FT232RL GND
HC-06 TXD - FT232RL RXD
HC-06 RXD - FT232RL TXD
PC running Windows 10, connect to FT232RL by USB.
Serial Monitor of Arduino IDE is used as a terminal to talk with Android.