The HC-05 is a widely used Bluetooth 2.0 module designed for wireless serial communication. It supports both master and slave modes, making it ideal for Arduino, ESP32, STM32, and other microcontroller-based projects.

Specifications

• Bluetooth Version: 2.0 + EDR (Class 2)
• Frequency: 2.4 GHz ISM band
• Modulation: GFSK (Gaussian Frequency Shift Keying)
• Operating Voltage: 3.6 V–6 V (typ. 5 V)
• Logic Level: 3.3 V (compatible with 5 V via voltage divider)
• Default Baud Rate: 9600 (configurable via AT commands)
• Communication Interface: UART (TX, RX)
• Range: ~10 m (open space)
• Roles: Master/Slave (configurable via AT commands)
• LED Indicator:
  - Blinking = waiting for connection
  - Steady = connected
• Dimensions: ~37 mm × 15 mm
• Antenna: Onboard PCB antenna
• Breakout Pins:
  - VCC, GND
  - TXD, RXD
  - EN (key pin for AT mode)

Features

• Enables wireless serial communication between microcontrollers and devices
• Supports AT command configuration for baud rate, role, and pairing
• Compatible with Arduino, ESP32, STM32, and Raspberry Pi
• Ideal for remote control, data logging, and wireless sensor networks
• Common use cases:
  - Wireless serial link between Arduino boards
  - Bluetooth-controlled robots and automation systems
  - Data transmission from sensors to mobile apps
  - DIY Bluetooth remote controls and IoT nodes