Good question! The HC-05 Bluetooth module isn't explicitly mentioned in the code because it communicates through the serial interface. The commands are processed by the line `command = Serial.read();`, which directly reads the input from the HC-05 module and controls the robot accordingly. If you're interested in learning more about how to use the HC-05 and an app to control devices, like turning a lamp on and off, check out my other video here: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-z1VubkUD264.html