Lesson 21--Microduino "Use Timer Interrupt"

Objective This lesson will introduc Microduino's timer interrupt. Use the timer interrupt to control LED by IO port 13. The time slot is 500ms. Equipment Microduino-Core Microduino-FT232R Other hardware equipment Breadboard Jumper one box Breadboard one piece LED one 220Ω resistor one USB Data cable one Experiment 1 Use library MsTimer2 Download MsTimer2 library：File:MsTimer2.zip Example： // LED connects to Pin 13 #include <MsTimer2.h> //Timer's head file void flash() //The interrupt service function { static boolean output = HIGH; digitalWrite(13, output); output = !output; } void setup() { pinMode(13, OUTPUT); MsTimer2::set(500, flash); //Set interrupt function, the timer is 500ms MsTimer2::start(); //Start timer } void loop() { } Result The state of LED changs every 500ms. Experiment 2 Use function millis() Example program unsigned long ledOn=500,ledOff=500; //Define the timer 500ms int ledStatus; //Define LED state, HIGH or LOW void setup() { pinMode(13,OUTPUT); digitalWrite(13,HIGH); ledStatus=HIGH; } void loop() { unsigned long nowtime=millis(); //Get the system current runned time if(ledStatus==HIGH) //Check LED state { if(nowtime>ledOn) //Check if time out happened { ledOn=nowtime; //Record time, the first time is 500ms ledOff=nowtime+500; //Calculate next time when LED state change digitalWrite(13,LOW); //LED off ledStatus=LOW; //Record current LED state, used next time } } else{ if(nowtime>ledOff) { ledOff=nowtime; ledOn=nowtime+500; digitalWrite(13,HIGH); ledStatus=HIGH; } } } Result Use the function mills()has the same result. LED state changed every 500ms. Function mills() can achieve the functionality of interrupt. The function of mills() is to obtain the system running time length, and the unit is ms. Up range is 9 hours 22 minutes, if beyond this time slot will start from zero. The return value of a function is unsigned long type. Players can use function mills() according to actual situation. The advantages of using function mills()is that take up the entire program running time is short, if use time delay function, in the delay time, the CPU can't do anything else.