• MCU board: ESP32-DEVKIT-V1
• Framework: Arduino via PlatformIO
• Sensors: SHT31-DIS-B2.5KS on I2C, HX711 load-cell ADC on two GPIOs
• I2C address: SHT31 ADDR is tied to GND, so address is 0x44

Ini
[env:esp32dev]
platform = espressif32
board = esp32dev
framework = arduino
monitor_speed = 115200
lib_deps =
    adafruit/Adafruit SHT31 Library@^2.2.2
    bogde/HX711@^0.7.5

Cpp
#include <Arduino.h>
#include <Wire.h>
#include <Adafruit_SHT31.h>
#include <HX711.h>

// Pin definitions from schematic
#define I2C_SDA_PIN       21   // U1 D21 -> I2C_SDA -> U2 SDA
#define I2C_SCL_PIN       22   // U1 D22 -> I2C_SCL -> U2 SCL
#define HX711_DOUT_PIN    32   // U1 D32 -> HX711_DOUT -> U3 DOUT
#define HX711_SCK_PIN     33   // U1 D33 -> HX711_SCK -> U3 PD_SCK

// Sensor configuration
#define SHT31_I2C_ADDR    0x44 // U2 ADDR tied to GND
#define READ_INTERVAL_MS  1000

Adafruit_SHT31 sht31 = Adafruit_SHT31();
HX711 scale;

unsigned long lastReadMs = 0;

// Calibration value: replace after calibration with known weight.
// Positive/negative sign depends on load-cell wiring polarity.
float hx711CalibrationFactor = 1.0f;
long hx711ZeroOffset = 0;

void initI2CAndSHT31() {
  Wire.begin(I2C_SDA_PIN, I2C_SCL_PIN);
  Wire.setClock(100000); // 100 kHz is conservative for initial bring-up

  if (!sht31.begin(SHT31_I2C_ADDR)) {
    Serial.println("ERROR: SHT31 not found at 0x44. Check SDA/SCL, 3V3, and GND.");
  } else {
    Serial.println("SHT31 detected at I2C address 0x44.");
    sht31.heater(false);
  }
}

void initHX711() {
  scale.begin(HX711_DOUT_PIN, HX711_SCK_PIN);

  Serial.println("Waiting for HX711...");
  if (scale.wait_ready_timeout(2000)) {
    // Use channel A, gain 128 by default in the HX711 library.
    scale.set_scale(hx711CalibrationFactor);
    scale.tare(10);
    hx711ZeroOffset = scale.get_offset();
    Serial.print("HX711 ready. Zero offset: ");
    Serial.println(hx711ZeroOffset);
  } else {
    Serial.println("ERROR: HX711 not ready. Check DOUT/SCK, 3V3, GND, and load-cell wiring.");
  }
}

void readSHT31(float &temperatureC, float &humidityPct, bool &ok) {
  temperatureC = sht31.readTemperature();
  humidityPct = sht31.readHumidity();
  ok = !isnan(temperatureC) && !isnan(humidityPct);
}

bool readHX711(long &rawValue, float &scaledValue) {
  if (!scale.wait_ready_timeout(1000)) {
    return false;
  }

  rawValue = scale.read_average(10);
  scaledValue = scale.get_units(10);
  return true;
}

void printSensorReadings() {
  float temperatureC = NAN;
  float humidityPct = NAN;
  bool shtOk = false;
  readSHT31(temperatureC, humidityPct, shtOk);

  long hxRaw = 0;
  float hxScaled = 0.0f;
  bool hxOk = readHX711(hxRaw, hxScaled);

  Serial.println("--- Sensor Readings ---");
  if (shtOk) {
    Serial.print("Temperature: ");
    Serial.print(temperatureC, 2);
    Serial.println(" °C");
    Serial.print("Humidity: ");
    Serial.print(humidityPct, 2);
    Serial.println(" %RH");
  } else {
    Serial.println("SHT31 read failed.");
  }

  if (hxOk) {
    Serial.print("HX711 raw: ");
    Serial.println(hxRaw);
    Serial.print("HX711 scaled units: ");
    Serial.println(hxScaled, 3);
  } else {
    Serial.println("HX711 read failed or device not ready.");
  }
}

void setup() {
  Serial.begin(115200);
  delay(500);
  Serial.println();
  Serial.println("ESP32 temperature + load-cell firmware starting...");

  initI2CAndSHT31();
  initHX711();

  Serial.println("Initialization complete.");
}

void loop() {
  unsigned long now = millis();
  if (now - lastReadMs >= READ_INTERVAL_MS) {
    lastReadMs = now;
    printSensorReadings();
  }
}

1. Upload the firmware and open the serial monitor.
2. With no load on the load cell, let scale.tare(10) zero the reading.
3. Place a known mass on the load cell.
4. Compute hx711CalibrationFactor = raw_change / known_units or use the HX711 library calibration examples.
5. Replace hx711CalibrationFactor = 1.0f with the measured value.
6. If the reading decreases when weight increases, invert the sign of the calibration factor or swap S+ and S-.

Bash
pio run
pio run -t upload
pio device monitor