• MCU/module: ESP32-C3-WROOM-02-N4
• Framework: Arduino on PlatformIO
• Sensor: Sensirion/Adafruit SHT4x-compatible I2C driver, SHT40 address 0x44
• Primary debug/programming: Native USB Serial/JTAG on GPIO18/GPIO19 via USB-C
• Recovery debug: UART TX/RX test pads on GPIO21/GPIO20

Ini
[env:esp32-c3-env-node]
platform = espressif32
board = esp32-c3-devkitm-1
framework = arduino
monitor_speed = 115200
upload_speed = 921600
build_flags =
  -DARDUINO_USB_MODE=1
  -DARDUINO_USB_CDC_ON_BOOT=1
lib_deps =
  adafruit/Adafruit SHT4x Library@^1.0.5
  adafruit/Adafruit BusIO@^1.16.1

Cpp
#include <Arduino.h>
#include <Wire.h>
#include <WiFi.h>
#include <Adafruit_SHT4x.h>

#define I2C_SDA_PIN          0
#define I2C_SCL_PIN          1
#define STATUS_LED_PIN       3
#define EFUSE_FLT_PIN        4
#define BUCK_PGOOD_PIN       5
#define BOOT_BUTTON_PIN      9
#define UART_RX_PIN          20
#define UART_TX_PIN          21

#define SENSOR_ADDR          0x44
#define SENSOR_PERIOD_MS     5000
#define WIFI_RETRY_LIMIT     20

const char* WIFI_SSID = "YOUR_SSID";
const char* WIFI_PASSWORD = "YOUR_PASSWORD";

Adafruit_SHT4x sht4;
unsigned long lastSensorReadMs = 0;

void initStatusPins() {
  pinMode(STATUS_LED_PIN, OUTPUT);
  digitalWrite(STATUS_LED_PIN, LOW);

  pinMode(EFUSE_FLT_PIN, INPUT_PULLUP);
  pinMode(BUCK_PGOOD_PIN, INPUT_PULLUP);
  pinMode(BOOT_BUTTON_PIN, INPUT_PULLUP);
}

void initRecoveryUart() {
  Serial1.begin(115200, SERIAL_8N1, UART_RX_PIN, UART_TX_PIN);
  Serial1.println("ESP32-C3 environmental node recovery UART online");
}

bool initSensor() {
  Wire.begin(I2C_SDA_PIN, I2C_SCL_PIN, 400000);
  if (!sht4.begin(&Wire)) {
    Serial.println("SHT40 not detected at 0x44");
    return false;
  }
  sht4.setPrecision(SHT4X_HIGH_PRECISION);
  sht4.setHeater(SHT4X_NO_HEATER);
  Serial.println("SHT40 initialized");
  return true;
}

void connectWiFi() {
  WiFi.mode(WIFI_STA);
  WiFi.begin(WIFI_SSID, WIFI_PASSWORD);
  Serial.print("Connecting to WiFi");

  int retries = 0;
  while (WiFi.status() != WL_CONNECTED && retries < WIFI_RETRY_LIMIT) {
    digitalWrite(STATUS_LED_PIN, !digitalRead(STATUS_LED_PIN));
    delay(500);
    Serial.print('.');
    retries++;
  }

  if (WiFi.status() == WL_CONNECTED) {
    digitalWrite(STATUS_LED_PIN, HIGH);
    Serial.printf("\nWiFi connected, IP=%s\n", WiFi.localIP().toString().c_str());
  } else {
    digitalWrite(STATUS_LED_PIN, LOW);
    Serial.println("\nWiFi not connected; continuing offline");
  }
}

bool powerPathHealthy() {
  bool efuseOk = digitalRead(EFUSE_FLT_PIN) == HIGH;
  bool buckOk = digitalRead(BUCK_PGOOD_PIN) == HIGH;
  if (!efuseOk) Serial.println("WARN: eFuse fault asserted");
  if (!buckOk) Serial.println("WARN: 3V3 buck power-good is low");
  return efuseOk && buckOk;
}

void readAndReportSensor() {
  sensors_event_t humidity, temp;
  if (!sht4.getEvent(&humidity, &temp)) {
    Serial.println("ERROR: SHT40 read failed");
    return;
  }

  Serial.printf("T=%.2f C, RH=%.2f %%\n", temp.temperature, humidity.relative_humidity);
  Serial1.printf("T=%.2f C, RH=%.2f %%\n", temp.temperature, humidity.relative_humidity);

  if (WiFi.status() == WL_CONNECTED) {
    // Placeholder for production data path: publish MQTT or HTTP POST here.
    // Keep this non-blocking in production firmware.
  }
}

void setup() {
  Serial.begin(115200);
  delay(500);
  Serial.println("USB-C WiFi/BLE Environmental Node starting");

  initStatusPins();
  initRecoveryUart();
  powerPathHealthy();

  if (!initSensor()) {
    for (int i = 0; i < 10; i++) {
      digitalWrite(STATUS_LED_PIN, !digitalRead(STATUS_LED_PIN));
      delay(100);
    }
  }

  connectWiFi();
}

void loop() {
  if (WiFi.status() != WL_CONNECTED) {
    digitalWrite(STATUS_LED_PIN, LOW);
    connectWiFi();
  }

  unsigned long now = millis();
  if (now - lastSensorReadMs >= SENSOR_PERIOD_MS) {
    lastSensorReadMs = now;
    powerPathHealthy();
    readAndReportSensor();
  }

  delay(10);
}

Bash
pio run
pio run -t upload
pio device monitor -b 115200