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.. _ar_interval:

1.11 Interval
=============

Overview
--------

Sometimes you need to do two things at once. For example you might want
to blink an LED while reading a button press. In this case, you can't
use delay(), because Arduino pauses your program during the delay(). If
the button is pressed while Arduino is paused waiting for the delay() to
pass, your program will miss the button press.

This sketch demonstrates how to blink an LED without using delay(). It
turns the LED on and then makes note of the time. Then, each time
through loop(), it checks to see if the desired blink time has passed.
If it has, it toggles the LED on or off and makes note of the new time.
In this way the LED blinks continuously while the sketch execution never
lags on a single instruction.

An analogy would be warming up a pizza in your microwave, and also
waiting some important email. You put the pizza in the microwave and set
it for 10 minutes. The analogy to using delay() would be to sit in front
of the microwave watching the timer count down from 10 minutes until the
timer reaches zero. If the important email arrives during this time you
will miss it.

What you would do in real life would be to turn on the pizza, and then
check your email, and then maybe do something else (that doesn't take
too long!) and every so often you will come back to the microwave to see
if the timer has reached zero, indicating that your pizza is done.


Components Required
-------------------

.. image:: img/list_1.11.png

* :ref:`cpn_mega2560`
* :ref:`cpn_breadboard`
* :ref:`cpn_wires`
* :ref:`cpn_led`
* :ref:`cpn_resistor`

Fritzing Circuit
----------------

In this example, we use digital pin 9 to drive the LED, and we attach
one side of the resistor to the corresponding digital pins. The longer
pin of LED (a positive electrode, referred to as anode) is connected to
the other side of the resistor. The shorter pin (a negative electrode,
referred to as cathode) of LED is attached to GND.

.. image:: img/image30.png

Schematic Diagram
-----------------

.. image:: img/image466.png

Code
----

.. note::

    * You can open the file ``1.11_interval.ino`` under the path of ``sunfounder_vincent_kit_for_arduino\code\1.11_interval`` directly.
    * Or copy this code into Arduino IDE 1/2.




.. raw:: html

    <iframe src=https://create.arduino.cc/editor/sunfounder01/9aa795a1-fcb1-4773-98bc-a353d3d21750/preview?embed style="height:510px;width:100%;margin:10px 0" frameborder=0></iframe>

When you finish uploading the codes to the Mega2560 board, you can see the LED uploading. 


Code Analysis
-------------


Declare the digital pin 9 as ledPin.

.. code-block:: arduino

    const int ledPin = 9;

Set the state of ledState to LOW to turn off the LED.

.. code-block:: arduino

    int ledState = LOW;

Initial a variable named previousMillis to store previous operating time of microcontroller.

.. code-block:: arduino

    unsigned long previousMillis = 0;     

Set the interval time to 1000ms (milliseconds).

.. code-block:: arduino

    const long interval = 1000; 

Set ledPin to OUTPUT mode.

.. code-block:: arduino

    pinMode(ledPin, OUTPUT);

In loop(), declare currentMillis to store the current time.

.. code-block:: arduino

    unsigned long currentMillis = millis();

When the interval between the current operating time and last updating time is larger than 1000ms, certain functions are triggered. Meanwhile, update the previousMillis to the current time for the next triggering that is to happen 1 second latter.  

.. code-block:: arduino

    if (currentMillis - previousMillis >= interval) {
        previousMillis = currentMillis;// save the last time you blinked the LED
    //...
    }

Here, certain functions executed at intervals are to change the state of LED. 

.. code-block:: arduino

    if (ledState == LOW) 
    {ledState = HIGH;} 
    else 
    {ledState = LOW;}
    digitalWrite(ledPin, ledState);

Phenomenon Picture
------------------

.. image:: img/image36.jpeg