How to convert delay to millis - arduino

Question

I have a simple code with delays.
I'd like to know how to convert this code to millis? Is there a function to do so?
long revers = 1000;
void setup() {
pinMode(D1, OUTPUT);
pinMode(D2, OUTPUT);
}
void loop() {
digitalWrite(D1, LOW);
delay(revers);
digitalWrite(D2, HIGH);
delay(revers);
digitalWrite(D2, LOW);
delay(revers);
digitalWrite(D1, HIGH);
delay(revers);
}

Answer 1

The basic concept is this: record the millis() at a given moment in a variable - say 'starttime'. Now, during every loop(), check the time that has elapsed by subtracting millis() from 'starttime'. If the elapsed time is greater than the delaytime you set, execute code. Reset the starttime to create a repeating pattern.
That may be too short of an explanation for you, so before you dive into the code, I highly advise you to read this introduction about using millis() for timing. It's lengthy, but it explains the principle extensively. This will help you understand the code below.
Lastly, there are several libraries written to make the use of timing easier. For instance the SimpleTimer-library, but you can google "arduino timer library" for others. I've included an example below.
1 second on, 3 seconds off:
unsigned long startMillis; //some global variables available anywhere in the program
unsigned long currentMillis;
const unsigned long period = 1000; //the value is a number of milliseconds
int fase; //value used to determine what action to perform
void setup() {
pinMode(7, OUTPUT);
pinMode(8, OUTPUT);
startMillis = millis(); //initial start time
fase = 0;
}
void loop() {
currentMillis = millis(); //get the current "time" (actually the number of milliseconds since the program started)
if (currentMillis - startMillis >= period) //test whether the period has elapsed
{
if (fase == 0)
{
digitalWrite(8, LOW);
startMillis = currentMillis; //IMPORTANT to save the start time of the current LED state.
fase = 1; //increment fase, so next action will be different
}
else if (fase == 1)
{
digitalWrite(7, HIGH);
startMillis = currentMillis;
fase = 2;
}
else if (fase == 2)
{
digitalWrite(7, LOW);
startMillis = currentMillis;
fase = 3;
}
else if (fase == 3)
{
digitalWrite(8, HIGH);
fase = 0;
startMillis = currentMillis;
}
}
}
Example of a flashing led using the SimpleTimer library
#include <SimpleTimer.h>
// the timer object
SimpleTimer timer;
int ledPin = 13;
// a function to be executed periodically
void repeatMe() {
digitalWrite(ledPin, !digitalRead(ledPin));
}
void setup() {
pinMode(ledPin, OUTPUT);
timer.setInterval(1000, repeatMe);
}
void loop() {
timer.run();
}