Documentation

// XIAO nRF52840 - Cycle the on-board RGB LED
// LEDs are active LOW (HIGH = off, LOW = on).
// Board: "Seeed XIAO nRF52840" (Seeed nRF52 mbed-enabled core)

#define LED_R LED_BUILTIN  // RED  (P0.26)
#define LED_G LED_GREEN    // GREEN (P0.30)
#define LED_B LED_BLUE     // BLUE  (P0.06)

void setup() {
  pinMode(LED_R, OUTPUT);
  pinMode(LED_G, OUTPUT);
  pinMode(LED_B, OUTPUT);
}

void all_off() {
  digitalWrite(LED_R, HIGH);
  digitalWrite(LED_G, HIGH);
  digitalWrite(LED_B, HIGH);
}

void loop() {
  all_off(); digitalWrite(LED_R, LOW); delay(400);
  all_off(); digitalWrite(LED_G, LOW); delay(400);
  all_off(); digitalWrite(LED_B, LOW); delay(400);
}

// XIAO nRF52840 - BLE peripheral advertising a Battery service
// Library: ArduinoBLE (Library Manager). Connect with nRF Connect on your phone.

#include <ArduinoBLE.h>

BLEService batteryService("180F");
BLEUnsignedCharCharacteristic batteryLevel("2A19", BLERead | BLENotify);

void setup() {
  Serial.begin(115200);
  while (!Serial && millis() < 3000) {}

  if (!BLE.begin()) {
    Serial.println("BLE init failed!");
    while (1) {}
  }

  BLE.setLocalName("ShillehTek-XIAO");
  BLE.setAdvertisedService(batteryService);
  batteryService.addCharacteristic(batteryLevel);
  BLE.addService(batteryService);
  batteryLevel.writeValue(100);

  BLE.advertise();
  Serial.println("Advertising as ShillehTek-XIAO");
}

void loop() {
  BLE.poll();

  static uint8_t level = 100;
  static unsigned long t = 0;
  if (millis() - t > 5000) {
    t = millis();
    level = (level > 0) ? level - 1 : 100;
    batteryLevel.writeValue(level);
    Serial.print("Battery: "); Serial.println(level);
  }
}

// XIAO nRF52840 - Read 12-bit analog on A0 (P0.02)
// Default reference is internal 0.6V * 6 = 3.6V; analogRead returns 0-4095.

void setup() {
  Serial.begin(115200);
  analogReadResolution(12);
}

void loop() {
  int raw = analogRead(A0);
  float volts = raw * (3.3f / 4095.0f);
  Serial.print(raw);
  Serial.print(" -> ");
  Serial.print(volts, 3);
  Serial.println(" V");
  delay(500);
}

# XIAO nRF52840 - CircuitPython Hello World
# Flash the official Adafruit CircuitPython UF2 for "Seeed XIAO nRF52840"
# (or "Seeed XIAO nRF52840 Sense" if you have the Sense version),
# then drop this as code.py on the CIRCUITPY drive.

import board
import digitalio
import time

red = digitalio.DigitalInOut(board.LED_RED)
red.direction = digitalio.Direction.OUTPUT

while True:
    red.value = False   # Active LOW: False = on
    time.sleep(0.25)
    red.value = True    # off
    time.sleep(0.25)