HC-05 is a popular Bluetooth module used to add wireless serial communication to microcontroller projects (like with Arduino, ESP32, etc.). It's based on the Bluetooth 2.0 standard and supports the Serial Port Protocol (SPP), making it suitable for classic Bluetooth communication (not BLE).
Bluetooth Version: 2.0 + EDR
Operating Voltage: 3.3V (but many breakout boards have onboard regulators, so they accept 5V)
Communication: UART (Rx/Tx)
Default Baud Rate: 9600 (configurable)
Modes:
Master – initiates connection
Slave – waits for connection (default)
AT Commands: Used to configure parameters like name, baud rate, and role