• MCU: ESP32-S3-WROOM-1-N8R8
• Framework: Arduino via PlatformIO
• Main peripherals: NAU7802 over I2C, SSD1306 OLED over I2C, microSD over SPI, BLE GATT, buttons, status LED.

Ini
[env:esp32-s3-devkitc-1]
platform = espressif32
board = esp32-s3-devkitc-1
framework = arduino
monitor_speed = 115200
build_flags =
  -DARDUINO_USB_MODE=1
  -DARDUINO_USB_CDC_ON_BOOT=1
lib_deps =
  sparkfun/SparkFun Qwiic Scale NAU7802 Arduino Library@^1.0.5
  adafruit/Adafruit SSD1306@^2.5.10
  adafruit/Adafruit GFX Library@^1.11.9
  h2zero/NimBLE-Arduino@^1.4.2

Cpp
#include <Arduino.h>
#include <Wire.h>
#include <SPI.h>
#include <SD.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>
#include <SparkFun_Qwiic_Scale_NAU7802_Arduino_Library.h>
#include <NimBLEDevice.h>

#define I2C_SDA_PIN 8
#define I2C_SCL_PIN 9
#define NAU_DRDY_PIN 7
#define SD_CS_PIN 10
#define SD_MOSI_PIN 11
#define SD_SCK_PIN 12
#define SD_MISO_PIN 13
#define SD_PWR_EN_PIN 21
#define BTN_TARE_PIN 4
#define BTN_START_STOP_PIN 5
#define STATUS_LED_PIN 6

#define SCREEN_WIDTH 128
#define SCREEN_HEIGHT 64
#define OLED_RESET -1
Adafruit_SSD1306 display(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire, OLED_RESET);
NAU7802 scale;

NimBLEServer *bleServer = nullptr;
NimBLECharacteristic *weightCharacteristic = nullptr;
static const char *SERVICE_UUID = "b7a8f7e0-41a3-42e5-8c6e-espresso0001";
static const char *WEIGHT_UUID  = "b7a8f7e0-41a3-42e5-8c6e-espresso0002";

float calibrationFactor = 1.0f;
long zeroOffset = 0;
bool timerRunning = false;
uint32_t shotStartMs = 0;
uint32_t lastSampleMs = 0;
uint32_t lastLogMs = 0;
File logFile;

bool pressed(uint8_t pin) { return digitalRead(pin) == LOW; }

void initBLE() {
  NimBLEDevice::init("EspressoScale");
  bleServer = NimBLEDevice::createServer();
  NimBLEService *service = bleServer->createService(SERVICE_UUID);
  weightCharacteristic = service->createCharacteristic(
      WEIGHT_UUID, NIMBLE_PROPERTY::READ | NIMBLE_PROPERTY::NOTIFY);
  weightCharacteristic->setValue("0.00,0");
  service->start();
  NimBLEAdvertising *adv = NimBLEDevice::getAdvertising();
  adv->addServiceUUID(SERVICE_UUID);
  adv->start();
}

void initDisplay() {
  if (!display.begin(SSD1306_SWITCHCAPVCC, 0x3C)) {
    Serial.println("OLED not found at 0x3C");
    return;
  }
  display.clearDisplay();
  display.setTextColor(SSD1306_WHITE);
  display.setTextSize(1);
  display.setCursor(0, 0);
  display.println("Smart Espresso Scale");
  display.display();
}

void initScale() {
  if (!scale.begin()) {
    Serial.println("NAU7802 not detected");
    return;
  }
  scale.setGain(NAU7802_GAIN_128);
  scale.setSampleRate(NAU7802_SPS_80);
  scale.calibrateAFE();
  delay(100);
  zeroOffset = scale.getAverage(16);
}

void initSD() {
  digitalWrite(SD_PWR_EN_PIN, HIGH);
  delay(20);
  SPI.begin(SD_SCK_PIN, SD_MISO_PIN, SD_MOSI_PIN, SD_CS_PIN);
  if (!SD.begin(SD_CS_PIN, SPI)) {
    Serial.println("microSD init failed; continuing without local log");
    return;
  }
  logFile = SD.open("/shots.csv", FILE_APPEND);
  if (logFile && logFile.size() == 0) {
    logFile.println("ms,grams,timer_ms");
    logFile.flush();
  }
}

float readGrams() {
  if (!scale.available()) return NAN;
  long raw = scale.getReading();
  return (raw - zeroOffset) / calibrationFactor;
}

void updateDisplay(float grams, uint32_t timerMs) {
  display.clearDisplay();
  display.setTextSize(2);
  display.setCursor(0, 0);
  display.printf("%6.1fg", grams);
  display.setTextSize(2);
  display.setCursor(0, 28);
  display.printf("%5.1fs", timerMs / 1000.0f);
  display.setTextSize(1);
  display.setCursor(0, 56);
  display.print(NimBLEDevice::getAdvertising()->isAdvertising() ? "BLE adv" : "BLE on");
  display.print(logFile ? " SD" : " noSD");
  display.display();
}

void logSample(float grams, uint32_t timerMs) {
  if (!logFile) return;
  logFile.printf("%lu,%.2f,%lu\n", millis(), grams, timerMs);
  if (millis() - lastLogMs > 1000) {
    logFile.flush();
    lastLogMs = millis();
  }
}

void handleButtons() {
  static bool lastTare = false, lastStart = false;
  bool tareNow = pressed(BTN_TARE_PIN);
  bool startNow = pressed(BTN_START_STOP_PIN);
  if (tareNow && !lastTare) zeroOffset = scale.getAverage(16);
  if (startNow && !lastStart) {
    timerRunning = !timerRunning;
    if (timerRunning) shotStartMs = millis();
  }
  lastTare = tareNow;
  lastStart = startNow;
}

void setup() {
  pinMode(STATUS_LED_PIN, OUTPUT);
  pinMode(SD_PWR_EN_PIN, OUTPUT);
  pinMode(BTN_TARE_PIN, INPUT_PULLUP);
  pinMode(BTN_START_STOP_PIN, INPUT_PULLUP);
  pinMode(NAU_DRDY_PIN, INPUT);
  digitalWrite(STATUS_LED_PIN, LOW);
  digitalWrite(SD_PWR_EN_PIN, LOW);

  Serial.begin(115200);
  delay(200);
  Wire.begin(I2C_SDA_PIN, I2C_SCL_PIN, 400000);
  initDisplay();
  initScale();
  initSD();
  initBLE();
}

void loop() {
  handleButtons();
  uint32_t now = millis();
  if (now - lastSampleMs >= 50) {
    lastSampleMs = now;
    float grams = readGrams();
    if (isnan(grams)) return;
    uint32_t timerMs = timerRunning ? now - shotStartMs : 0;
    updateDisplay(grams, timerMs);
    logSample(grams, timerMs);
    char payload[32];
    snprintf(payload, sizeof(payload), "%.2f,%lu", grams, timerMs);
    weightCharacteristic->setValue(payload);
    weightCharacteristic->notify();
    digitalWrite(STATUS_LED_PIN, !digitalRead(STATUS_LED_PIN));
  }
}

• Build: pio run
• Flash over native USB: hold BOOT, tap RESET, then pio run -t upload
• Monitor: pio device monitor