Data Communication Principles
Working Principle
FSC-BT691 Bluetooth data transmission module realizes wireless communication between devices based on the BLE (Bluetooth Low Energy) protocol.
BLE: Adopts an event-driven low-power architecture, and defines a “Service-Characteristic” model through the GATT protocol to realize intermittent small data interaction (such as sensor data), which is suitable for IoT devices.
The module can send AT commands or perform transparent data transmission with host devices (mobile phones/MCUs) via UART to complete connection establishment, data exchange, and status management.
As shown in the figure above, the FSC-BT691 Bluetooth module is used to replace physical wires in full-duplex communication. Devices such as MCU (left) send data to the FSC-BT691 Bluetooth module (left) through TXD. After the RXD port of the Bluetooth module receives the UART data, it automatically transmits the data via radio waves over the air to the remote FSC-BT691 Bluetooth module. The remote Bluetooth module (right) receives the over-the-air data and sends it to local devices such as MCU (right) through TXD.
MCU-to-Module Communication
This diagram shows a connection schematic between a main control MCU (Microcontroller Unit) and an FSC-BT691 Bluetooth module. Command interaction between the main control and the Bluetooth module is realized through cross-connected UART, supporting wireless communication functions, which is applicable to scenarios such as IoT devices and remote control.
UART Communication Interface ：The transmission end of the main MCU (MCU_TX) is cross-connected to the receiving end of the Bluetooth module (UART_RX), and the receiving end of the main MCU (MCU_RX) is similarly connected to the transmission end of the Bluetooth module (UART_TX), forming a bidirectional data transmission channel;
Power Supply and Grounding : The Bluetooth module is powered with 3.3V through the VDD_3V3 pin and shares a common ground (GND) with the main MCU to ensure level compatibility and signal stability;
Module-to-Module Communication
Two FSC-BT691 Bluetooth modules can establish a Bluetooth connection automatically after being powered on.
FSC-BT691 module has master-slave device functionality. The left module can be configured as a master device, and the right module as a slave device. The master device can implement operations such as Bluetooth scanning, connection establishment, data transmission, and disconnection by sending commands. Among them, the device that actively initiates a Bluetooth connection is defined as the master device, and the device that receives the connection request is the slave device.
Module-to-Phone Communication
Why is an APP required on the 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 through the built-in settings program of the mobile phone, such as 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 SPP/GATT protocols), a specific mobile application (such as the FeasyBlue app) is generally required to connect to such modules.
Communication Application
Bluetooth Module side (FSC-BT691) : It will continuously send broadcast data outward after being powered on.
Mobile Phone side : The FeasyBlue App can search and obtain the broadcast packet of the FSC-BT691 module, and initiate a MAC address/UUID connection request to the module (FSC-BT691), while acquiring all services and characteristics provided by the device. After a successful connection, the Bluetooth module (FSC-BT691) will pull high the connection status pin and report the connection status command (valid in command mode) to notify the host that the Bluetooth connection is successful.
Host side: Data can be sent to the remote (mobile phone side) Bluetooth through the UART via the Bluetooth module, and the remote (mobile phone side) Bluetooth can also send data to the host.