In many of the sketches shared by us have the millis() instead of delay(). Not always it is possible to explain a function within a guide on how to do a thing. In this article, we will explain about millis() and provide some easy examples so that you can reproduce yourself.
It is normal that the Arduino users initially use the delay() function. The main reason is the blink example is the thing that almost every newbie starts with. While the delay() function is easy to use it has side effects.
One of the main complain (or side effects) of the delay() function is that it stops all activity on the Arduino until the delay is finished. It is not quite true, but this is what usually the problem becomes.
We already know how to set the pinMode() of input and output. Any pin including pins A1, A2, A3 other than 0 and 1 can be used as digital inputs.
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There are two type of delay functions, first is delay() and second is delayMicroseconds(). Both functions are near the same except unit. When we are adding a delay of 1 second, the microcontroller cannot proceed till that 1 second is passed. It is like a pause function. This essentially hampers the performance and speed. If we want to control two LEDs using two pushbuttons, then the delay() function will not work. Arduino 2 Push Button One LED Switch On/Off is a situation where we still could use the delay() function.
This is the traditional example of Blink :
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int led = 13; void setup() { pinMode(led, OUTPUT); } void loop() { digitalWrite(led, HIGH); // turn the LED on (HIGH is the voltage level) delay(1000); // wait for a second digitalWrite(led, LOW); // turn the LED off by making the voltage LOW delay(1000); // wait for a second } |
Blink without Delay is the example where the delay() function is replaced by millis() :
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unsigned long interval=1000; // the time we need to wait unsigned long previousMillis=0; // millis() returns an unsigned long. bool ledState = false; // state variable for the LED void setup() { pinMode(13, OUTPUT); digitalWrite(13, ledState); } void loop() { unsigned long currentMillis = millis(); // grab current time // check if "interval" time has passed (1000 milliseconds) if ((unsigned long)(currentMillis - previousMillis) >= interval) { ledState = !ledState; // "toggles" the state digitalWrite(13, ledState); // sets the LED based on ledState // save the "current" time previousMillis = millis(); } } |
Above is the shortest, easiest “Blink without Delay” sketch. The advantage is that if you want to add two LEDs in the above sketch, then add in this way :
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unsigned long previousMillisLED12=0; unsigned long previousMillisLED13=0; |
You need not to alter this :
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void loop() { // get current time stamp // only need one for both if-statements unsigned long currentMillis = millis(); |
Slightly complex version can be this example :
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int ledPin = 13; // the number of the LED pin int ledState = LOW; // ledState used to set the LED unsigned long previousMillis = 0; // will store last time LED was updated long OnTime = 250; // milliseconds of on-time long OffTime = 750; // milliseconds of off-time void setup() { // set the digital pin as output: pinMode(ledPin, OUTPUT); } void loop() { // check to see if it's time to change the state of the LED unsigned long currentMillis = millis(); if((ledState == HIGH) && (currentMillis - previousMillis >= OnTime)) { ledState = LOW; // Turn it off previousMillis = currentMillis; // Remember the time digitalWrite(ledPin, ledState); // Update the actual LED } else if ((ledState == LOW) && (currentMillis - previousMillis >= OffTime)) { ledState = HIGH; // turn it on previousMillis = currentMillis; // Remember the time digitalWrite(ledPin, ledState); // Update the actual LED } } |
As you can see, using the millis() function will make a sketch more complicated but the sketch becomes significantly more mature.
Now the above sketches will run happily deducting the current time by turning the LED on and off. But if you code in a manner to compare, after just over 49 days, the value returned by millis() will get so large that it will not fit in an unsigned long variable and it will roll over to zero and start incrementing again. After handling the basics, you should read the below webpages:
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https://arduino.stackexchange.com/questions/12587/how-can-i-handle-the-millis-rollover https://www.learncpp.com/cpp-tutorial/unsigned-integers-and-why-to-avoid-them/ https://www.gammon.com.au/millis |
