Arduino Cookbook

Chapter 12. Using Time and Dates

12.0. Introduction

Managing time is a fundamental element of interactive computing. This chapter covers built-in Arduino functions and introduces many additional techniques for handling time delays, time measurement, and real-world times and dates.

12.1. Creating Delays

Problem

You want your sketch to pause for some period of time. This may be some number of milliseconds, or a time given in seconds, minutes, hours, or days.

Solution

The Arduino delay function is used in many sketches throughout this book. delay pauses a sketch for the number of milliseconds specified as a parameter. (There are 1,000 milliseconds in one second.) The sketch that follows shows how you can use delay to get almost any interval:

/*
 * delay sketch
 */

const long oneSecond = 1000;  // a second is a thousand milliseconds
const long oneMinute = oneSecond * 60;
const long oneHour   = oneMinute * 60;
const long oneDay    = oneHour * 24;


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

void loop()
{
  Serial.println("delay for 1 millisecond");
  delay(1);
  Serial.println("delay for 1 second");
  delay(oneSecond);
  Serial.println("delay for 1 minute");
  delay(oneMinute);
  Serial.println("delay for 1 hour");
  delay(oneHour);
  Serial.println("delay for 1 day");
  delay(oneDay);
  Serial.println("Ready to start over");
}

Discussion

The delay function has a range from one one-thousandth of a second to around 25 days (just less than 50 days if using an unsigned long variable type; see Chapter 2 for more on variable types).