The connection method between a Bluetooth module and the main MCU mainly depends on the type of module you choose. Considering the smart ring project you are working on, there are usually two mainstream connection solutions:
1. UART Transparent Transmission Mode (The simplest, suitable for quick start-up)
If you are using a pre-flashed module with integrated Bluetooth firmware (such as E104-BT09, MS52SF1, etc., based on Telink TLSR8208), they usually communicate with the MCU via UART transparent transmission.
Connection method:
TXD (Module Transmit) connects to the MCU's RXD (Receive)
RXD (Module Receive) connects to the MCU's TXD (Transmit)
GND connects to GND (Common Ground)
VCC connects to 3.3V (Power Supply)
Working principle: The MCU only needs to send standard AT commands via UART to configure Bluetooth parameters (such as device name, transmit power, etc.). After the connection is established, any data sent by the MCU through the UART will be directly forwarded via Bluetooth, and vice versa. This method doesn't require you to dive deep into the complex Bluetooth protocol stack, making it perfect for rapid development.
2. Protocol Docking Mode (Mainstream solution, suitable for deep customization)
If you are developing deeply based on the Telink SDK (for example, using Tuya Smart's BLE solution), in addition to basic UART communication, you also need to connect some status control pins to achieve low-power management and status synchronization.
Basic connections:
TX / RX: Cross-connected with the MCU, used for transmitting Bluetooth protocol data packets (DP data reporting and receiving).
Advanced control pins (Highly recommended):
Low-power control pin (Wakeup/Sleep): The MCU uses this pin to put the module into deep sleep mode. For battery-powered devices like smart rings that are extremely sensitive to power consumption, this pin is crucial.
Connection status notification pin (Link/State): When the phone connects or disconnects via Bluetooth, the module will output a high or low logic level through this GPIO to notify the MCU. This allows the MCU to switch working states in time (e.g., sleeping when disconnected, staying active when connected).
RST (Reset pin): The MCU can force a reboot of the Bluetooth module by pulling this pin low.
💡 Hardware connection suggestions for smart rings:
Since the internal space of a smart ring is extremely limited and it is powered by a battery, please pay close attention to the following two points when designing the PCB or flying wires:
Low-power design: Be sure to connect the module's low-power control pin. When the MCU detects low battery voltage or the device is idle, it can actively put the Bluetooth module into deep sleep to prevent abnormal power drain.
Stable power supply: Bluetooth draws a large instantaneous current when transmitting signals. It is recommended to connect a suitable filtering capacitor between the module's VCC and GND pins to prevent voltage fluctuations from causing the module to restart unexpectedly.
