Technical Documentation - LifeLink [ESP32-S3]

app_main: System entry point, hardware init, and sub-system startup.

void app_main(void) {
    i2c_init();             // Bus I2C initialization
    ble_spp_server_init();  // Bluetooth startup
    ui_init();              // LVGL GUI initialization
    xTaskCreate(read_sensor_data, "sensor_read_task", 4096, NULL, 10, NULL);
}

sensor_read_task: Sync with QMI8658 IMU and real-time fall detection logic.

void read_sensor_data(void *arg) {
    while (1) {
        if (qmi.getDataReady()) {
            qmi.getAccelerometer(acc.x, acc.y, acc.z);
            // Fall Detection State Machine...
        }
        vTaskDelay(pdMS_TO_TICKS(10));
    }
}

MAX30102: Asynchronous health tracking (BPM & SpO2) using FIFO buffers and FFT.

while (max30102.available()) {
    redBuffer[i] = max30102.getRed();
    irBuffer[i] = max30102.getIR();
    if (full) fft_process(red, ir, 100, &hr, &spo2);
}

gsm_task: Network monitoring and auto-recovery for the SIM800L module.

void gsm_status_task(void *arg) {
    while (1) {
        if (gsm_check_network() != ESP_OK) {
            gsm_a6_init(); // Re-init on network loss
        }
        vTaskDelay(pdMS_TO_TICKS(10000));
    }
}

ble_spp_server_task: NimBLE stack for Flutter app communication.

void ble_spp_server_host_task(void *param) {
    nimble_port_run(); // NimBLE stack main loop
    nimble_port_freertos_deinit();
}

AXP2101 PMIC: A smart power controller managing voltages for the ESP32 and peripherals.

• ALDO1 (3.3V): Powers main sensors and logic components.
• ALDO2 (1.8V): Dedicated power for the AMOLED digital interface.
• Boot-Loop Protection: Register 0x10 bit 1 (PWROFF) is cleared at startup to prevent the hardware from shutting down after 1s (critical fix for Waveshare boards).
• Charging: Configured for 500mA with a 4.2V target voltage for Li-Po batteries.

AMOLED Power Optimization: AMOLED screens consume power only for active pixels.

// Energy saving logic
void reset_screen_timer() {
    if (!screen_is_on) {
        esp_lcd_panel_disp_on_off(panel_handle, true); // Wake up
        ESP_LOGI("PWR", "Screen WAKE");
    }
    last_touch_time = esp_timer_get_time() / 1000;
}

Software Timeout: After 15 seconds of inactivity, the system calls esp_lcd_panel_disp_on_off(panel_handle, false), turning off all pixels to minimize draw while background tasks remain active.

TCA9554 IO Expander: A secondary chip at 0x20 that physically controls the Screen EN (Enable) pins.

// P2 pin on TCA9554 controls LCD_VCC_EN
uint8_t tca_val[] = {0x01, 0x27}; // Sets P0, P1, P2 High
i2c_master_write_to_device(I2C_NUM, TCA9554_ADDR, tca_val, 2, timeout);

BLE Communication Protocol: The app utilizes the flutter_blue_plus library for low-energy Bluetooth data exchange.

• Service UUID: 4fafc201-1fb5-459e-8fcc-c5c9c331914b
• Characteristic UUID: beb5483e-36e1-4688-b7f5-ea07361b26a8
• Subscription Model: The app subscribes to characteristic notifications, enabling real-time data streaming from the hardware without excessive polling.

BleService Architecture: Implemented as a Singleton service for robust connection management.

// BleService (Flutter) subscription logic
await targetCharacteristic.setNotifyValue(true);
targetCharacteristic.onValueReceived.listen((value) {
    // Parsing bytes into vital signs data
    _dataController.add(value); 
});

Core Features:

• Live Dashboard: Visual representation of Heart Rate and SpO2 levels received directly from the bracelet.
• Alarm Mirroring: Upon fall detection, the phone triggers a high-priority sound alert and displays the user's location on a map.
• Contact Management: Remote configuration of SOS telephone numbers via the BLE channel.