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===== Oak: blinking the on-board LED =====

A common first project with a microcontroller is to "blink" an LED. It's very simple, is a good way to get familiar with the basics of writing code, and many boards (including the Oak) include an on-board LED, so no additional components are necessary. A tutorial using additional LEDs can be found [[oak:tutorials:leds|here]].

===== Components used =====

^ Part       ^ Quantity          ^Identification^
| Oak with soldered headers |1| |

While we only need an Oak for this lesson, be sure to make sure you have completed the steps in the "Getting Started" section of the [[http://digistump.com/wiki/oak?redirect=1|tutorials]]. In particular, ensure that your Oak is associated with [[https://www.particle.io/|particle.io]] and that your Arduino IDE  is [[http://digistump.com/wiki/oak/tutorials/arduino|properly configured]].

===== Concepts =====

=== digitalWrite() ===

''digitalWrite(pin_number, value)'' is the command used to send a ''HIGH'' or ''LOW'' voltage to the pin of a microcontroller. In the case of the Oak, pin 1 is connected to a small surface mounted LED on the board. We will be turning the voltage on and off to this pin to turn this LED on and off.

=== pinMode() ===

Microcontrollers can often change the functionality of a pin internally by using code. For pins that are meant to "listen," for example when connected to a sensor, we use ''pinMode(pin_number, INPUT)''. When we plan to "send" a signal, we use ''pinMode(pin_number, OUTPUT)''. Since we will be sending voltage //to// the LED, we will use ''OUTPUT'' for the mode of pin 1.


=== delay() ===

The ''delay(milliseconds)'' function is used to take a break from the code that's being run. Code is written in lines, and each line is read and execute one at a time. When the microcontroller encounters the ''delay()'' function, it waits for that many milliseconds before moving on to the next line. This is important for timing the blinking of the LED.


===== Code =====

=== The blink sketch ===

This code will make the on-board LED connected to pin 1 blink. It will turn on for 1 second, and then off for one second, over and over:

<code>
// comments are inserted by putting two forward
// slashes at the beginning of a line

// the setup() loop sets pinModes, starts things like Serial,
// and is run once when the Oak powers on
void setup()
{                

  // initialize digital pin 1 as an output.
  pinMode(1, OUTPUT); //LED on Oak

}


// the loop() routine runs over and over again
void loop()
{

  // turn pin 1 "on" by making the voltage HIGH)
  // the light will turn on here
  digitalWrite(1, HIGH);
  
  // wait a second (1000 milliseconds)
  // since we told the voltage to be on,
  // it will stay on while the Oak waits
  delay(1000);
  
  // turn the LED off by making the voltage LOW
  digitalWrite(1, LOW);

  // wait another second
  // since the voltage was low when the Oak
  // started to wait, it will stay off during this time
  delay(1000);

}
</code>

This code tells the Oak that we will be using pin 1 as an output, and then loops over and over sending a ''HIGH'' signal to pin 1 (turns the LED on), waits 1 second, and then turns the LED off by sending a ''LOW'' signal.

You can find a template like this in the Arduino IDE under ''File -> Examples -> Oak Examples -> Start''. Otherwise, start a new sketch and copy/paste the above into your file. Make sure the port and board selections are correct and then upload the code (the button above the text window with a right arrow icon). You should see this in the message area at the bottom of the Arduino window:

<code>
Sketch uses 259,578 bytes (24%) of program storage space. Maximum is 1,040,368 bytes.
Global variables use 51,048 bytes (62%) of dynamic memory, leaving 30,872 bytes for local variables. Maximum is 81,920 bytes.
Using config file at: /path/to/.oak/config.json
Sending file to cloud, to flash device-name (Device ID: 123456789)
Flashing..........
Rebooting Oak.........
Oak Ready
</code>

Once the Oak receives the code, it will blink as shown here (if the image isn't animated, click to open in a new tab):

[[http://digistump.com/wiki/_media/oak/tutorials/blink-simple.gif|{{oak:tutorials:blink-simple.gif?300}}]]

===== Code: changing LED behavior =====

Now that you have a general idea of how to turn a light on and off, what else could you do? How might you make the blink shorter or longer? What do you think this changed code might do? (Hint: compare the delay values after each step!)

<code>
void setup()
{                

  pinMode(1, OUTPUT); //LED on Oak

}

// the loop() routine runs over and over again
void loop()
{

  // faster blink
  digitalWrite(1, HIGH);
  delay(100);
  
  // longer off time
  digitalWrite(1, LOW);
  delay(2000);

}
</code>

With this code, the light will blink for a shorter time and stay off longer.

=== Code: a for() loop ===

You can also define the delays using variables and loops to make things more interesting:

<code>
// now we've added two variables to hold our
// on and off time delays
// the "int" variable is able to hold integer values
int on_time;
int off_time;

void setup() 
{                

  pinMode(1, OUTPUT); //LED on Oak

}

void loop()
{

  // the for() loop will initialize a new temporary variable, i
  // it runs until i >= 500, adding 50 each time
  for(int i = 0; i < 500; i = i+50)
  {

    // the on time will equal i (0, 50, 100, ...)
    on_time = i;
    
    // the off time will equal 500 - i (500, 450, 400, ...)
    off_time = 500 - i;

    digitalWrite(1, HIGH);
    delay(on_time);
  
    digitalWrite(1, LOW);
    delay(off_time);
  
  }
  
}
</code>

Here is what happens each time the loop runs:

^time through loop ^i ^on_time ^off_time|
|1|0|0|500|
|2|50|50|450|
|3|100|100|300|
|.|.|.|.|
|.|.|.|.|
|10|450|450|50|

When the ''for()'' loop above runs, ''i'' is equal to 0. It calculatesIf you upload this code, you will see this (click for enlarged view in new tab):

[[http://digistump.com/wiki/_media/oak/tutorials/loop-changing-blink.gif|{{oak:tutorials:loop-changing-blink.gif?300}}]]


Congratulations! You've taken your first steps with the Oak. Take a look at some of the other [[http://digistump.com/wiki/oak?redirect=1|tutorials]] for more!
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