Getting started with Arduino

6.1 Getting started — first circuit (LED)

• An Arduino is a small programmable microcontroller board with input/output (I/O) pins.
• It runs simple C/C++ programs called sketches.

Every sketch has two main functions:

void setup() {
  // runs once when the board starts
  pinMode(13, OUTPUT);
}

void loop() {
  // runs over and over forever
  digitalWrite(13, HIGH);
  delay(1000);
  digitalWrite(13, LOW);
  delay(1000);
}

• pinMode(pin, OUTPUT) — set the pin's direction.
• digitalWrite(pin, HIGH/LOW) — turn the pin ON or OFF (5V or 0V).
• delay(ms) — pause for that many milliseconds.

6.2 Breadboards and buttons

• A breadboard is a reusable board with hidden wires that connect rows of holes — you push components in instead of soldering.
• A button connects a pin to either +5V or GND when pressed.
• Use a pull-down or pull-up resistor so the pin reads a clear HIGH or LOW.

int buttonPin = 2;

void setup() {
  pinMode(buttonPin, INPUT);
}

void loop() {
  if (digitalRead(buttonPin) == HIGH) {
    digitalWrite(13, HIGH);
  } else {
    digitalWrite(13, LOW);
  }
}

6.3 Latching buttons using variables

A latch remembers a state — e.g. one press turns the LED on, the next turns it off, even though the button is only momentarily pushed.

int ledState = LOW;

void loop() {
  if (digitalRead(buttonPin) == HIGH) {
    ledState = !ledState;     // flip
    digitalWrite(13, ledState);
    delay(300);               // debounce
  }
}

Variables in Arduino C: int, bool, float, String. Always declare with a type.

6.4 Analogue input and output

Analogue input

• analogRead(A0) returns a value from 0 to 1023.
• Used with sensors that give a varying voltage (e.g. light sensor, temperature sensor, potentiometer).
• Serial.begin(9600) + Serial.println(value) sends data back to the computer to view in the Serial Monitor.

Analogue output (PWM)

• Arduino digital pins can only be HIGH or LOW. PWM (Pulse Width Modulation) fakes analogue output by switching very fast — average voltage is between 0V and 5V.
• analogWrite(pin, value) with value 0–255 — used to dim LEDs, control motor speed, etc.
• Only works on certain pins (marked with ~).

6.5 Subroutines

Pull repeated code into a function, just like in Python:

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

void loop() {
  blink(13, 3);
  delay(1000);
}

• void means the function doesn't return a value.
• Parameters allow the same code to do different things.

6.6 Making a useful system

Combine inputs, outputs and logic to build something real.

• Temperature sensor — outputs a voltage that depends on temperature; read with analogRead.
• LDR (light sensor) — resistance changes with light; in a divider circuit, gives a varying analogue voltage.
• Motors need more current than the Arduino can give directly — use a transistor (e.g. NPN) as a switch, with the motor powered separately.