• MCU: ESP32-C3-WROOM-02-N4
• Framework: Arduino for ESP32 using PlatformIO
• Board target: esp32-c3-devkitm-1 as a practical starting target for ESP32-C3 modules

Ini
[env:espresso_scale]
platform = espressif32
board = esp32-c3-devkitm-1
framework = arduino
monitor_speed = 115200
build_flags =
  -D ARDUINO_USB_MODE=1
  -D ARDUINO_USB_CDC_ON_BOOT=1
lib_deps =
  bogde/HX711@^0.7.5
  olikraus/U8g2@^2.35.30

Cpp
#include <Arduino.h>
#include <Wire.h>
#include <WiFi.h>
#include <HX711.h>
#include <U8g2lib.h>

#define HX711_DOUT_PIN   0
#define HX711_SCK_PIN    1
#define BAT_SENSE_PIN    3
#define BTN_TARE_PIN     4
#define I2C_SDA_PIN      5
#define I2C_SCL_PIN      6
#define BTN_MODE_PIN     7

#define VBAT_TOP_OHMS    1000000.0f
#define VBAT_BOTTOM_OHMS 330000.0f
#define ADC_MAX_COUNTS   4095.0f
#define ADC_REF_VOLTS    3.3f

#define SCALE_READ_INTERVAL_MS 100
#define DISPLAY_INTERVAL_MS    250
#define LONG_PRESS_MS          800

HX711 scale;
U8G2_SSD1306_128X64_NONAME_F_HW_I2C display(U8G2_R0, U8X8_PIN_NONE);

static float calibrationFactor = 1000.0f;  // TODO: calibrate with known mass
static unsigned long lastScaleRead = 0;
static unsigned long lastDisplay = 0;
static float weightGrams = 0.0f;
static bool timerRunning = false;
static unsigned long timerStartMs = 0;

float readBatteryVoltage() {
  uint16_t raw = analogRead(BAT_SENSE_PIN);
  float adcVoltage = (raw / ADC_MAX_COUNTS) * ADC_REF_VOLTS;
  return adcVoltage * ((VBAT_TOP_OHMS + VBAT_BOTTOM_OHMS) / VBAT_BOTTOM_OHMS);
}

bool pressed(uint8_t pin) {
  static unsigned long lastDebounce[10] = {0};
  static bool lastState[10] = {false};
  bool nowPressed = digitalRead(pin) == LOW;
  uint8_t idx = pin < 10 ? pin : 0;
  if (nowPressed != lastState[idx] && millis() - lastDebounce[idx] > 40) {
    lastDebounce[idx] = millis();
    lastState[idx] = nowPressed;
    return nowPressed;
  }
  return false;
}

void initScale() {
  scale.begin(HX711_DOUT_PIN, HX711_SCK_PIN);
  scale.set_scale(calibrationFactor);
  scale.tare(20);
}

void initDisplay() {
  Wire.begin(I2C_SDA_PIN, I2C_SCL_PIN);
  display.begin();
  display.setFont(u8g2_font_6x12_tf);
}

void updateDisplay() {
  float vbat = readBatteryVoltage();
  unsigned long elapsed = timerRunning ? (millis() - timerStartMs) / 1000UL : 0;

  display.clearBuffer();
  display.setCursor(0, 12);
  display.print("Smart Espresso Scale");
  display.setCursor(0, 30);
  display.print("Weight: ");
  display.print(weightGrams, 1);
  display.print(" g");
  display.setCursor(0, 46);
  display.print("Timer: ");
  display.print(elapsed);
  display.print(" s");
  display.setCursor(0, 62);
  display.print("VBAT: ");
  display.print(vbat, 2);
  display.print(" V");
  display.sendBuffer();
}

void setup() {
  Serial.begin(115200);
  delay(300);
  Serial.println("Smart Espresso Scale booting");

  WiFi.mode(WIFI_OFF); // keep RF quiet during precision measurements by default

  pinMode(BTN_TARE_PIN, INPUT_PULLUP);
  pinMode(BTN_MODE_PIN, INPUT_PULLUP);
  analogReadResolution(12);
  analogSetPinAttenuation(BAT_SENSE_PIN, ADC_11db);

  initDisplay();
  initScale();
  updateDisplay();
}

void loop() {
  unsigned long now = millis();

  if (pressed(BTN_TARE_PIN)) {
    Serial.println("Tare requested");
    scale.tare(20);
  }

  if (pressed(BTN_MODE_PIN)) {
    timerRunning = !timerRunning;
    if (timerRunning) timerStartMs = now;
    Serial.printf("Timer %s\n", timerRunning ? "started" : "stopped");
  }

  if (now - lastScaleRead >= SCALE_READ_INTERVAL_MS) {
    lastScaleRead = now;
    if (scale.is_ready()) {
      weightGrams = scale.get_units(3);
      Serial.printf("Weight: %.2f g, VBAT: %.2f V\n", weightGrams, readBatteryVoltage());
    } else {
      Serial.println("HX711 not ready");
    }
  }

  if (now - lastDisplay >= DISPLAY_INTERVAL_MS) {
    lastDisplay = now;
    updateDisplay();
  }
}

Bash
pio run
pio run -t upload
pio device monitor