Code: telling the brain what to do

A board does nothing until you give it a program: a list of instructions written in a coding language. You write it on a computer in the free Arduino IDE app, then send it to the board through the USB cable. This is called uploading.

Think in "if-then"

Most IoT programs are just smart if-then rules:

• If it is dark, then turn on the light.
• If the soil is dry, then start the pump.
• If someone moves, then sound the buzzer.

Every Arduino program has two parts

• setup() runs once when the board starts, like getting ready in the morning.
• loop() runs again and again forever, like checking your homework over and over.

Your first program: blink a light

void setup() {
  pinMode(LED_BUILTIN, OUTPUT);     // get the light ready
}

void loop() {
  digitalWrite(LED_BUILTIN, HIGH);  // light ON
  delay(1000);                      // wait 1 second
  digitalWrite(LED_BUILTIN, LOW);   // light OFF
  delay(1000);                      // wait 1 second
}

Text after // is a comment: a note for humans that the board ignores.

A smart night lamp in a few lines

void setup() {
  pinMode(13, OUTPUT);              // the lamp LED is on pin 13
}

void loop() {
  int light = analogRead(A0);       // read the light sensor
  if (light < 300) {                // if it is dark...
    digitalWrite(13, HIGH);         // ...turn the lamp on
  } else {
    digitalWrite(13, LOW);          // otherwise, turn it off
  }
}