HC-05 Bluetooth module features
The HC-05 is a popular Bluetooth module allowing wireless communication between devices. HC-05 Bluetooth serial communication module is a data transmission module based on Bluetooth Specification V2.0 with EDR Bluetooth protocol. The wireless operating frequency band is 2.4GHz ISM, and the modulation method is GFSK. The maximum transmit power of the module is 4dBm, the receiving sensitivity is -85dBm and the onboard PCB antenna can achieve communication at a distance of 10 meters.
The module’s LED light can visually determine the Bluetooth connection status. The module uses CSR’s BC417 chip and supports AT commands. Users can change roles (master and slave modes) and serial port baud rate, device name, and other parameters as needed, making it flexible to use.
HC-05 Bluetooth module principle
The communication diagram of the HC-05 Bluetooth module is as follows: the two device main control chips or microcontrollers are connected to their respective Bluetooth modules, that is, the serial port control pins of the main control chip and the Bluetooth module are cross-connected. Because the Bluetooth module has its own transparent transmission function, simply speaking, the Bluetooth module forwards whatever data is transmitted through the serial port of the main control chip. Therefore, the serial port of the main control chip can also be regarded as a serial port with wireless transmission.
Since Bluetooth is divided into master and slave, the module defaults to slave mode when shipped from the factory. If you need to set it as a host, you need to set up Bluetooth through AT commands.
Connection diagram of HC-05 Bluetooth module and microcontroller
When the HC-05 Bluetooth module is connected to an MCU whose power supply system is 3.3V, the serial port cross connection is sufficient (the RX of the module is connected to the TX of the MCU, and the TX of the module is connected to the RX of the MCU); when the module is connected to an MCU whose power supply system is 5V, You can connect a 220R~1K resistor in series to the RX end of the module and then connect it to the TX of the MCU. The TX of the module is directly connected to the RX of the MCU, without a series resistor. (Note: Please first confirm that the MCU you are using recognizes 3.0V or above as a high level, otherwise a 3.3V/5V level conversion circuit is required; I am using the STC89C52 microcontroller, which is directly connected and does not need to add a level conversion circuit. circuit).