Note: I understand this is a very old example, and the recommendation is to use the updated example shared above.
However, I had some free time and decided to power up my 20-year-old Arduino and Bluetooth module.
To my surprise, I was still able to make it work using this classic example:
In this example we will connect an Android device to an Arduino using class Bluetooth with the HC 05 module. Working with this module is simple. Connect the power and gnd pins and connect the HC05 RX pin to an Arduino TX pin and the HC05 TX pin to an Arduino RX pin. The HC05 RX pin expects 3.3...
www.b4x.com
In the Arduino code, I set it up to send dummy temperature data, I can read that and also control ON/OFF the led-Arduino