• MCU module: Raytac MDBT50Q-P1MV2, nRF52840 inside.
• Main logic rail: 3V0.
• USB sense: module VBUS tied to VBUS_5V.
• VDDH is tied directly to 3V0. The previous Schottky D4 VBUS_5V-to-VDDH path was removed so the MCU remains powered correctly when USB is unplugged.
• DCCH uses 10 uH inductor L3 to VDD/3V0 and 1 uF C14 to GND.
• QSPI flash: W25Q64JVSSIQ, 3V-compatible substitute for requested W25Q64JWSSIQ because the JW family is 1.8 V.
• SGP41: VDD is powered from 1V8_SGP41 for the sensing/hotplate supply, while VDDH is powered from 3V0 for the digital/I2C interface supply. This matches the intended split-supply topology and keeps I2C compatible with the 3V0 pull-ups.

• BME280: 0x76, because SDO is pulled to GND.
• SGP41: 0x59.
• SPS30: typically 0x69 for the Sensirion I2C interface.

Ini
[env:nrf52840_wearable]
platform = nordicnrf52
board = adafruit_feather_nrf52840
framework = arduino
monitor_speed = 115200
lib_deps =
  adafruit/Adafruit BME280 Library
  adafruit/Adafruit Unified Sensor
  sensirion/Sensirion I2C SGP4x
  sensirion/Sensirion Core

Cpp
#include <Arduino.h>
#include <Wire.h>
#include <Adafruit_BME280.h>
#include <SensirionI2CSgp41.h>

// Pin definitions from schematic
static constexpr uint8_t PIN_I2C_SDA = 26;      // P0.26 -> I2C_SDA
static constexpr uint8_t PIN_I2C_SCL = 27;      // P0.27 -> I2C_SCL
static constexpr uint8_t PIN_AIN2_BAT = 4;      // P0.04 / AIN2 -> battery divider midpoint
static constexpr uint8_t PIN_LED_STATUS = 13;   // P0.13 -> R12 -> D5 green
static constexpr uint8_t PIN_LED_ERR = 14;      // P0.14 -> R13 -> D6 red
static constexpr uint8_t PIN_USER_BUTTON = 15;  // P0.15 -> SW1 -> GND

// QSPI flash pin mapping, for board-definition / Nordic SDK configuration
static constexpr uint8_t PIN_QSPI_CS  = 17;     // P0.17
static constexpr uint8_t PIN_QSPI_CLK = 19;     // P0.19
static constexpr uint8_t PIN_QSPI_IO0 = 21;     // P0.21
static constexpr uint8_t PIN_QSPI_IO1 = 22;     // P0.22
static constexpr uint8_t PIN_QSPI_IO2 = 23;     // P0.23
static constexpr uint8_t PIN_QSPI_IO3 = 32;     // P1.00 is encoded as 32 in many nRF52 Arduino cores

static constexpr uint8_t BME280_ADDR = 0x76;
static constexpr uint8_t SGP41_ADDR = 0x59;
static constexpr uint8_t SPS30_ADDR = 0x69;

Adafruit_BME280 bme;
SensirionI2CSgp41 sgp41;

uint16_t sgp41ConditioningTicks = 0;
uint32_t lastSensorMs = 0;

float readBatteryVolts() {
  // Divider is 100k / 100k, so VBAT/VSYS at ADC pin is half the rail.
  // analogRead() range depends on Arduino core ADC reference and resolution.
  // Use analogReadMilliVolts() if your selected core supports it.
#if defined(ARDUINO_ARCH_NRF52)
  uint16_t raw = analogRead(PIN_AIN2_BAT);
  float adcVolts = (raw / 1023.0f) * 3.0f;  // default approximation; calibrate in firmware
#else
  uint16_t raw = analogRead(PIN_AIN2_BAT);
  float adcVolts = (raw / 1023.0f) * 3.3f;
#endif
  return adcVolts * 2.0f;
}

bool probeI2C(uint8_t address) {
  Wire.beginTransmission(address);
  return Wire.endTransmission() == 0;
}

void setupGpio() {
  pinMode(PIN_LED_STATUS, OUTPUT);
  pinMode(PIN_LED_ERR, OUTPUT);
  pinMode(PIN_USER_BUTTON, INPUT_PULLUP);
  digitalWrite(PIN_LED_STATUS, LOW);
  digitalWrite(PIN_LED_ERR, LOW);
}

void setupI2C() {
  Wire.setPins(PIN_I2C_SDA, PIN_I2C_SCL);
  Wire.begin();
  Wire.setClock(400000);
}

bool setupBME280() {
  if (!bme.begin(BME280_ADDR, &Wire)) {
    Serial.println("BME280 not found at 0x76");
    return false;
  }

  bme.setSampling(
    Adafruit_BME280::MODE_NORMAL,
    Adafruit_BME280::SAMPLING_X2,
    Adafruit_BME280::SAMPLING_X16,
    Adafruit_BME280::SAMPLING_X1,
    Adafruit_BME280::FILTER_X16,
    Adafruit_BME280::STANDBY_MS_1000
  );
  return true;
}

bool setupSGP41() {
  sgp41.begin(Wire);
  uint16_t serialNumber[3] = {0, 0, 0};
  int16_t error = sgp41.getSerialNumber(serialNumber);
  if (error) {
    Serial.print("SGP41 serial read failed, error: ");
    Serial.println(error);
    return false;
  }
  Serial.print("SGP41 serial: ");
  Serial.print(serialNumber[0], HEX);
  Serial.print(serialNumber[1], HEX);
  Serial.println(serialNumber[2], HEX);
  return true;
}

void readSensors() {
  float tempC = bme.readTemperature();
  float humidity = bme.readHumidity();
  float pressurePa = bme.readPressure();
  float batteryV = readBatteryVolts();
  bool buttonPressed = (digitalRead(PIN_USER_BUTTON) == LOW);

  // SGP41 raw measurement. Use default compensation values initially:
  // relative humidity ticks = 0x8000, temperature ticks = 0x6666.
  uint16_t srawVoc = 0;
  uint16_t srawNox = 0;
  int16_t error = 0;

  if (sgp41ConditioningTicks < 10) {
    error = sgp41.executeConditioning(0x8000, 0x6666, srawVoc);
    sgp41ConditioningTicks++;
  } else {
    error = sgp41.measureRawSignals(0x8000, 0x6666, srawVoc, srawNox);
  }

  if (error) {
    digitalWrite(PIN_LED_ERR, HIGH);
    Serial.print("SGP41 read error: ");
    Serial.println(error);
  } else {
    digitalWrite(PIN_LED_ERR, LOW);
  }

  digitalWrite(PIN_LED_STATUS, !digitalRead(PIN_LED_STATUS));

  Serial.print("T="); Serial.print(tempC, 2); Serial.print(" C, ");
  Serial.print("RH="); Serial.print(humidity, 1); Serial.print(" %, ");
  Serial.print("P="); Serial.print(pressurePa / 100.0f, 1); Serial.print(" hPa, ");
  Serial.print("VBAT/VSYS="); Serial.print(batteryV, 3); Serial.print(" V, ");
  Serial.print("SGP41 VOCraw="); Serial.print(srawVoc); Serial.print(", NOxraw="); Serial.print(srawNox); Serial.print(", ");
  Serial.print("button="); Serial.println(buttonPressed ? "pressed" : "released");

  if (probeI2C(SPS30_ADDR)) {
    Serial.println("SPS30 present at 0x69");
  } else {
    Serial.println("SPS30 not detected at 0x69");
  }
}

void setup() {
  Serial.begin(115200);
  delay(500);
  Serial.println("MDBT50Q-P1MV2 wearable bring-up");

  setupGpio();
  setupI2C();

  bool ok = true;
  ok &= setupBME280();
  ok &= setupSGP41();

  digitalWrite(PIN_LED_ERR, ok ? LOW : HIGH);
  digitalWrite(PIN_LED_STATUS, ok ? HIGH : LOW);
}

void loop() {
  const uint32_t now = millis();
  if (now - lastSensorMs >= 1000) {
    lastSensorMs = now;
    readSensors();
  }
}

1. Power the board from USB and battery/system supply and confirm 3V0, 1V8_SGP41, VBUS_5V, VSYS, and 5V_SPS30 are present.
2. Program via TC2030 SWD: VTref=3V0, SWDIO, SWDCLK, nRESET, GND.
3. Verify I2C scan finds BME280 at 0x76 and SGP41 at 0x59.
4. Connect SPS30 and verify it appears at 0x69.
5. Calibrate battery voltage measurement because the ADC reference and raw-to-voltage scaling depend on the selected nRF52 Arduino core/board package.
6. If production firmware needs external QSPI flash, create a custom nRF52840 board definition or Zephyr board overlay that assigns P0.17/P0.19/P0.21/P0.22/P0.23/P1.00 to QSPI.