Article #19 : Arduino Timers

Introduction :

When we start learning about microcontrollers, and especially Arduino in our case, the first program that you have written was most probably the famous blinking LED program. In that program you certainly used to call the delay() function to set the time interval between blinks. The only thing is that delay() sets Arduino on pause mode, so how we can blink the LED while still using Arduino for doing other tasks at the same time like sending serial data for example ? That’s why we are going to learn about the Timer library to facilitate this task. 

The library :

The library Timer has a simple functioning principle. After adding the library to our project, we can create a variable of type Timer, then we update it in the loop function and finally give some instructions to our timer to perform the tasks like blinking an LED for 100ms for example.

Basic Commands :

As said previously, we have to import the Timer library to our program.

#include “Timer”

Then, we have to create our variable of type timer :

Timer timer;

Also, we have to update our newly created timer in the loop function as follows :

void loop(){

Timer.update();

}

Now we don’t need to use the delay() function anymore. We have our timer to count time in the program.

The most used functions in the Timer library are the following :

int every(long period, callback, int repeatCount)

Run the 'callback' every 'period' milliseconds for a total of 'repeatCount' times.

int after(long duration, callback)

Run the 'callback' once after 'period' milliseconds.

int oscillate(int pin, long period, int startingValue, int repeatCount)

Toggle the state of the digital output 'pin' every 'period' milliseconds 'repeatCount' times. 

The pin's starting value is specified in 'startingValue', which should be HIGH or LOW.

int pulse(int pin, long period, int startingValue)

Toggle the state of the digital output 'pin' just once after 'period' milliseconds. 

The pin's starting value is specified in 'startingValue', which should be HIGH or LOW.

int update()

Must be called from 'loop'. This will service all the events associated with the timer.

Examples :

The following example is a program that passes a pin from a state to another for a set period of time only once. To do it we need to implement the ‘pulse’ method.

#include "Timer.h"

Timer t;

int pin = 13; 

void setup()

{

  pinMode(pin, OUTPUT);

  t.pulse(pin, 10 * 60 * 1000, HIGH); // 10 minutes  

}

void loop()

{

  t.update();

}

The update method in the loop function takes only few milliseconds to run, and the program can continue executing other instructions while the timer counts the time in the setup function.

The second example is program that toggles the pin 13 from a state to another every 100 ms and reads the analog pin 0 from the serial monitor every 2 seconds.

#include "Timer.h"

Timer t;

int pin = 13;

void setup()

{

  Serial.begin(9600);

  pinMode(pin, OUTPUT);

  t.oscillate(pin, 100, LOW); // la fonction qui fait clignoter la led toutes les 100 ms

  t.every(1000, envoi); // et celle-ci qui appelle la fonction 'envoi' toutes les secondes

} 

void loop()

{

  t.update();

} 

void envoi() // fonction qui envoie par liaison série l'entrée du pin 0

{

  Serial.println(analogRead(0));

}

References :

http://playground.arduino.cc/Code/Timer