Data Communication Principles
Communication Principle
FSC-BT3721V Bluetooth BLE data transmission modules enable wireless communication between devices based on the BLE (Bluetooth Low Energy) protocol.
BLE : It adopts an event-driven low-power architecture and defines a “Service-Characteristic” model through the GATT protocol to realize intermittent small-data interaction (e.g., sensor data), making it suitable for IoT (Internet of Things) devices.
The module sends AT commands or transparent transmission data to the host device (mobile phone/MCU) via UART to complete connection establishment, data exchange, and status management.
As shown in the diagram, the Bluetooth module is used to replace the physical wires in full-duplex communication. A device such as a microcontroller unit (MCU) (on the left) sends data to the left-side Bluetooth module via its TXD pin. After the RXD pin of the left-side Bluetooth module receives the serial data, it automatically transmits the data via radio waves to the remote Bluetooth module (on the right). The right-side remote Bluetooth module then receives the over-the-air data and sends it to the local device (e.g., an MCU) on the right via its TXD pin.
MCU-to-Module Communication
This diagram illustrates a connection schematic between a main control MCU (Microcontroller Unit) and an FSC-BT3721V Bluetooth module. Through cross-connected serial ports, command interaction between the main controller and the Bluetooth module is achieved, enabling wireless communication functionality. This setup is suitable for scenarios such as IoT (Internet of Things) devices and remote control.
Serial Communication Interface：The transmitting end of the main MCU (MCU_TX) is cross-connected to the receiving end of the Bluetooth module (UART_RX), and similarly, the receiving end of the MCU (MCU_RX) is connected to the transmitting end of the Bluetooth module (UART_TX), forming a bidirectional data transmission channel.
Power Supply and GND：The Bluetooth module is connected to 3.3V via the VDD_3V3 pin and shares a common GND with the main MCU to ensure level compatibility and signal stability.
Module-to-Module Communication
Two FSC-BT3721V Bluetooth modules can establish a Bluetooth connection automatically upon power-on.
The module can act as a master device to connect to slave devices. The host can send commands to control the module for Bluetooth scanning, connection establishment, data transmission, and connection disconnection.
Module-to-Phone Communication
Why is an APP required on a mobile phone for Bluetooth connection and communication?
The native Bluetooth function of mobile phones only supports general scenarios, such as audio transmission and file transfer. Some Bluetooth peripheral devices can be connected via the built-in settings program of the mobile phone, including Bluetooth speakers, Bluetooth headsets, Bluetooth keyboards, Bluetooth mice, etc. When a Bluetooth peripheral device cannot be connected by the mobile phone's native settings program (for example, the Bluetooth module only supports the SPP/GATT protocol), a specific mobile application (such as the FeasyBlue app) usually needs to be installed on the mobile phone to connect to such a module.
Communication Application Diagram
Bluetooth Module（FSC-BT3721V）：Upon power-on, it will continuously send out broadcast data;
Mobile Terminal：The broadcast packets can be obtained through searching, and a connection request can be initiated to the module side (FSC-BT3721V). After a successful connection, the Bluetooth module (FSC-BT3721V) will pull up the connection status pin and respond to the indication command (effective in command mode) to notify the host side that the Bluetooth connection is successful;
Host：Data can be sent to the remote (mobile phone side) Bluetooth via the serial port through the Bluetooth module, and the remote (mobile phone side) Bluetooth can also send data to the host .