Lab Session 2: Timers

Estimated time: 1.5h (1 session)

Description

The goal of this session is to learn the different ways a microcontroller can perform timing operations. As seen previously, the delay() function can be used to create a wait for the required amount of time. However, to solve slightly more complex problems, it becomes necessary to use timers, which allow us to interrupt the normal execution of the program in order to handle a periodic event.

1. Working with real hardware

1.1. Using an external library - Ticker

The Arduino Ticker Library allows you to create easily Ticker callbacks, which can call a function in a predetermined interval The following example shows how to perform timing operations using the Ticker library and the attach() or attach_ms() functions.

#include <M5Core2.h>   // M5Stack Core2 library
#include <Ticker.h>    // Ticker library

#define LED_PIN 14     // GPIO pin where the LED is connected on the M5Core2

Ticker blinker;        // Create a Ticker object. It will call a function at regular intervals.

/*
  This function (callback) will be called by the Ticker at the configured time interval.
  It simply toggles the LED state:
    - digitalRead(LED_PIN) reads the current state (HIGH/LOW)
    - ! inverts that state
    - digitalWrite writes the inverted state back to the pin
*/
void changeState()
{
    digitalWrite(LED_PIN, !(digitalRead(LED_PIN))); 
}

void setup() 
{
    M5.begin();          // Initialize the M5Core2 hardware (display, I2C, etc.)
    pinMode(LED_PIN, OUTPUT); // Configure the LED pin as an output

    // Initialize the Ticker to call changeState() periodically.
    // attach() accepts time in seconds (here 0.5 s = 500 ms).
    // If you prefer milliseconds, use attach_ms(milliseconds, callback).
    blinker.attach(0.5, changeState); 
}

void loop() 
{      
    // Empty: the Ticker handles the periodic LED toggling asynchronously.
}

Connect an LED to pin 14 of the M5Core2 and modify this example so that the LED blinks every second instead of every 500 ms.

1.2. Use hardware timers

However, as stated in the Ticker library documentation, "The library use no interupts of the hardware timers and works with the micros() / millis() function." This means that our ability to develop an application using different timer configurations or to implement multitasking applications would be highly limited if we restrict ourselves to using this library.

Perform the previous exercise again, but in this case use an interrupt generated directly by the timer, and configure it so that the LED turns ON and OFF every second. Verify with a watch that it works correctly.

2. Working in simulation

You can do exactly the same exercises in simulation. Just use the same circuit with the LED we used in the previous lab sessions.