Arduino (C/C++)

TL; DR;

See also : https://wiki.seeedstudio.com/XIAO-RP2040-with-Arduino/

Hello World

For this “Hello World”, we will “just” make a LED blink.

The sections were created to help you starting with Arduino and to give the Fab Academy 2025 programming recitation.

Please note that for the next code and simulations, examples will be given on PIN25, which is the blue builtin LED of your XIAO RP2040, or the green LED of your Raspberry Pico board. On the related Wokwi simulation, we will use PIN0 with a connected LED just because the (very) small LED represented on the board is a bit too discrete.

Loop : “Infinite” while

Blinking the onboard blue led, minimalistic code. Based on an inifinite while because the condition next to it is declared “always true”, so that it will last forever.

// Set pin 25 (= blue led on XIAO RP2040, builtin led on RPi Pico) as an output
const int ledPin = 25;

void setup() {
  pinMode(ledPin, OUTPUT);
}

void loop() {
  // Infinite loop to blink the LED
  while (true) {
    digitalWrite(ledPin, !digitalRead(ledPin)); // Change LED's status
    delay(500);                                 // Wait for 0.5 seconds
  }
}

Wokwi simulation : https://wokwi.com/projects/422329075777941505

Loop : “conditional” while

This code will set a variable “a” to the value 10, then decrement it (a-=1) on each loop until a becomes 0. The code will then stop. This will thus make your LED blink 5 times. (every loop toggle its status)

// Set pin 25 (= blue led on XIAO RP2040, builtin led on RPi Pico) as an output
const int ledPin = 25;
int a = 10;

void setup() {
  pinMode(ledPin, OUTPUT);
}

void loop() {
  // Make your led blink 5 times (=10/2 because toggle)
  while (a > 0) {
    a -= 1;           // equivalent to a=a-1
    digitalWrite(ledPin, !digitalRead(ledPin)); // Change LED's status
    delay(500);       // Wait for 0.5 seconds
  }
}

Wokwi simulation : https://wokwi.com/projects/422329385597616129

Loop : for

// Set pin 25 (= blue led on XIAO RP2040, builtin led on RPi Pico) as an output
const int ledPin = 25;

void setup() {
  pinMode(ledPin, OUTPUT);
}

void loop() {
  // Make your led blink 5 times (=10/2 because toggle)
  for (int i = 0; i < 10; i++) {
    digitalWrite(ledPin, !digitalRead(ledPin)); // Change LED's status
    delay(500);                                 // Wait for 0.5 seconds
  }
}

Wokwi simulation : https://wokwi.com/projects/422329575967662081

Function Call

// Set pin 25 (= blue led on XIAO RP2040, builtin led on RPi Pico) as an output
const int ledPin = 25;

void blink_led(int times) {
  for (int i = 0; i < times; i++) {
    digitalWrite(ledPin, HIGH);
    delay(200);
    digitalWrite(ledPin, LOW);
    delay(300);
  }
}

void setup() {
  pinMode(ledPin, OUTPUT);
}

void loop() {
  for (int i = 0; i < 5; i++) {
    blink_led(i);         // Blink i times
    delay(2000);          // Wait for 2 seconds
  }
}

Wokwi simulation : https://wokwi.com/projects/422329711912410113

Using arrays

This code will define an array containing five different values and then will make the LED blink that amount of times (using the blink_led() function).

// Array with 5 pre-defined values
int values[] = {3, 7, 2, 5, 1};

// Set pin 25 (= blue led on XIAO RP2040, builtin led on RPi Pico) as an output
const int ledPin = 25;

void blink_led(int times) {
  for (int i = 0; i < times; i++) {
    digitalWrite(ledPin, HIGH);
    delay(200);
    digitalWrite(ledPin, LOW);
    delay(300);
  }
}

void setup() {
  pinMode(ledPin, OUTPUT);
}

void loop() {
  for (int i = 0; i < 5; i++) {
    blink_led(values[i]);         // Blink i times
    delay(2000);                  // Wait for 2 seconds
  }
}

Wokwi simulation : https://wokwi.com/projects/422329831991158785

Branching : if then else

// Set pin 25 (= blue led on XIAO RP2040, builtin led on RPi Pico) as an output
const int ledPin = 25;

void blink_led(int times) {
  for (int i = 0; i < times; i++) {
    digitalWrite(ledPin, HIGH);
    delay(200);
    digitalWrite(ledPin, LOW);
    delay(300);
  }
}

void setup() {
  pinMode(ledPin, OUTPUT);
}

void loop() {
  for (int i = 0; i < 5; i++) {
    if (i % 2 == 0) {       // if i is even
      blink_led(2);
    } else {
      blink_led(1);         // if i is odd
    }
    delay(2000);
  }
}

Wokwi simulation : https://wokwi.com/projects/422330021890421761

Using libraries

Libraries let you do more complex stuffs with a few lines of code.

Note : this example must still be checked : please repport any error you might find.

#include <Adafruit_NeoPixel.h>

// Number of LEDs and pin
const int leds_n = 16;
const int np_pin = 6;

// Initialize NeoPixel strip
Adafruit_NeoPixel pixels(leds_n, np_pin, NEO_GRB + NEO_KHZ800);

// Define colors
uint32_t colors[] = {
  pixels.Color(255, 0, 0),   // RED
  pixels.Color(0, 255, 0),   // GREEN
  pixels.Color(0, 0, 255),   // BLUE
  pixels.Color(255, 255, 0), // YELLOW
  pixels.Color(0, 255, 255), // TURQUOISE
  pixels.Color(255, 0, 255)  // PURPLE
};
const int color_n = sizeof(colors) / sizeof(colors[0]);

int pixel_index = 0;
int color_index = 0;

void setup() {
  pixels.begin();
  pixels.setBrightness(50);
  pixels.show(); // Initialize all pixels to 'off'
}

void loop() {
  pixels.setPixelColor(pixel_index, colors[color_index]);
  pixels.show();
  // Serial.print(pixel_index); Serial.println(colors[color_index]);
  pixel_index++;
  if (pixel_index == leds_n) {
    pixel_index = 0;
    color_index = (color_index + 1) % color_n;
  }
  delay(100);
}

Coming soon : PIO & Debugging basics

Playground / sandbox board