How to read GNSS / GPS NMEA sentences on Yuz Badge using custom firmware?

Here is the hardware configuration for the GNSS receiver on the Yuz Badge:

1. Pinout Mapping

• GNSS TX (ESP32 RX): GPIO 44 (UART1_RXD)
• GNSS RX (ESP32 TX): GPIO 43 (UART1_TXD)
• GNSS Power Enable (EN / VCC control): GPIO 17 (Active HIGH). You must set gpio_set_level(GPIO_NUM_17, 1) to power on the GNSS LDO.
• TIMEPULSE (1PPS): Routed to GPIO 18 for sub-millisecond time synchronization interrupt.

2. Default Configuration

• Baud Rate: 9600 bps (8 data bits, no parity, 1 stop bit).
• Protocol: NMEA 0183 standard sentences (GNGGA, GNRMC, GNVTG, GNZDA).

3. ESP-IDF Initialization Snippet

#define GNSS_UART_NUM     UART_NUM_1
#define GNSS_TX_PIN       GPIO_NUM_43
#define GNSS_RX_PIN       GPIO_NUM_44
#define GNSS_EN_PIN       GPIO_NUM_17

void init_gnss(void) {
    // Power on GNSS module
    gpio_set_direction(GNSS_EN_PIN, GPIO_MODE_OUTPUT);
    gpio_set_level(GNSS_EN_PIN, 1);
    vTaskDelay(pdMS_TO_TICKS(100)); // allow LDO to stabilize

    uart_config_t uart_config = {
        .baud_rate = 9600,
        .data_bits = UART_DATA_8_BITS,
        .parity = UART_PARITY_DISABLE,
        .stop_bits = UART_STOP_BITS_1,
        .flow_ctrl = UART_HW_FLOWCTRL_DISABLE,
        .source_clk = UART_SCLK_DEFAULT,
    };
    uart_param_config(GNSS_UART_NUM, &uart_config);
    uart_set_pin(GNSS_UART_NUM, GNSS_TX_PIN, GNSS_RX_PIN, UART_PIN_NO_CHANGE, UART_PIN_NO_CHANGE);
    uart_driver_install(GNSS_UART_NUM, 1024 * 2, 0, 0, NULL, 0);
}

If you test indoors, place the badge near an open window or connect an active external patch antenna to get a 3D satellite fix.