ATmega328P Timer Overview

PWM Frequencies (prescaler)

analogWrite() Resolution

Blink with millis() (non-blocking)

const int LED = 13;
unsigned long prev = 0;
const long interval = 500;

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

void loop() {
  unsigned long now = millis();
  if (now - prev >= interval) {
    prev = now;
    digitalWrite(LED, !digitalRead(LED));
  }
}

Read Analog + Serial Print

void setup() { Serial.begin(9600); }

void loop() {
  int val = analogRead(A0);       // 0–1023
  float volts = val * (5.0 / 1023.0); // convert to volts
  Serial.print("A0: ");
  Serial.print(volts);
  Serial.println(" V");
  delay(500);
}

I2C Scanner

#include <Wire.h>

void setup() {
  Serial.begin(9600);
  Wire.begin();
  Serial.println("Scanning I2C bus...");
  for(byte a=1; a<127; a++){
    Wire.beginTransmission(a);
    if(Wire.endTransmission()==0){
      Serial.print("Found: 0x");
      Serial.println(a, HEX);
    }
  }
}

Debounce Button

const int BTN=2; bool state, last;
unsigned long debounce=50, t=0;

void setup(){ pinMode(BTN, INPUT_PULLUP); }

void loop(){
  bool reading = !digitalRead(BTN); // active low
  if(reading != last) t = millis();
  if(millis()-t > debounce) state = reading;
  last = reading;
}

Multiple LEDs in series

Specs — Arduino Uno Rev3