In-Depth: Interfacing HC05 Bluetooth Module with Arduino

The core of this system is the Arduino Uno, which acts as the central processing and communication hub, paired with the HC-05 Bluetooth module to enable wireless serial communication. The HC-05 module communicates with the Arduino using Universal Asynchronous Receiver-Transmitter (UART) protocol, translating serial data streams into radio frequency signals that can be paired and exchanged with an Android smartphone running a terminal application. Because the Arduino Uno operates on standard 5V logic levels while the HC-05 module is a 3.3V-tolerant device, a voltage level shifting circuit—constructed using 1K and 2K resistors in a voltage divider configuration—is strictly required on the Arduino's TX to HC-05 RX line to step down the signal and prevent hardware damage. Power is distributed using a breadboard and jumper wires to supply the necessary voltage rails from the Arduino to the Bluetooth module. Once the physical circuit is wired and the Arduino IDE is used to flash the appropriate sketch, characters and telemetry data can be sent bi-directionally between the smartphone and the microcontroller. The Android device acts as a remote master or slave terminal, letting the user transmit commands or receive real-time text feedback from the Arduino over the air, effectively replacing a physical USB tether with a wireless serial link.