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So, you've got an Oak all set up and ready to go. Now it's time to put its wireless
abilities to work!  This lesson will introduce ''Particle.variable()'' a method provided by [[https://www.particle.io/|particle.io]] for reading data from the Oak. The basic idea is pretty simple, and we'll start with a simple push button. Feel free to review the [[oak:tutorials:button|tutorial on buttons]] for a refresher. In addition, please do take a look at the [[https://docs.particle.io/reference/firmware/core/#particle-variable-|official documentation]].

==== Requirements ====

This lesson will use (in addition to an Oak):

  * a tactile push button
  * a photoresistor
  * jumper wires
  * a breadboard
  * a resistor (10k ohms is good)

Optionally, you can install [[https://curl.haxx.se/download.html|curl]] to get data from the Particle API, however pasting the links into a browser works just as well.


==== Example: getting the state of a button ====

Here's the circuit we'll use, which reads the button (pulled up to ''Vcc'' through a 10k resistor) on pin 10:

[[http://digistump.com/wiki/_media/oak/tutorials/button-pullup.png|{{http://digistump.com/wiki/_media/oak/tutorials/button-pullup.png?400}}]]


The code we'll start with is as follows:

<code>
int button;

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

  // use the on-board LED to illuminate when the button is pressed
  pinMode(1, OUTPUT);
  
  // initialize the digital pin as an input
  pinMode(10, INPUT);

  // Particle.variable() takes two options:
  // 1) the name of the varialbe to access in the GET request
  // 2) the name of the local variable that holds the value to report
  Particle.variable("button", button);

}


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

  button = digitalRead(10);

  // for debugging, it's helpful to have a way to know
  // that the button is being reported properly

  if(button == HIGH) {digitalWrite(1, HIGH); }
  if(button == LOW) { digitalWrite(1, LOW); }

}
</code>

The only thing we did other than reading a button as usual is to attach ''Particle.variable()'' to that variable and give it a name we can use through the web to access the value. After uploading the code above, press the button to check that the on-board LED illuminates:

[[http://digistump.com/wiki/_media/oak/tutorials/button-led-off.jpg|{{oak:tutorials:button-led-off.jpg?300 }}]]
[[http://digistump.com/wiki/_media/oak/tutorials/button-led-on.jpg|{{ oak:tutorials:button-led-on.jpg?310 }}]]

This confirms that the variable ''button'' is being read correctly. Next, make sure you have your ''device_id'' and ''access_token'' as described in the [[oak:tutorials:particle-id-token|Particle API wiki entry]].

[pic of device id]
[pic of access token]

If you have ''curl'' installed, open a command prompt/terminal, and type the following (replacing ''id_here'' and ''token_here'' with the appropriate values). Otherwise, type out the URL somewhere you can copy/paste from, and visit that page in a browser.

<code>
$ curl https://api.particle.io/v1/devices/id_here/button?access_token=token_here
</code>

Hopefully this is what you get in return!

<code>
$ curl https://api.particle.io/v1/devices/id_here/button?access_token=token_here
{
  "cmd": "VarReturn",
  "name": "button",
  "result": 1,
  "coreInfo": {
    "last_app": "",
    "last_heard": "2016-03-19T20:51:18.623Z",
    "connected": true,
    "last_handshake_at": "2016-03-19T20:32:30.268Z",
    "deviceID": "12345678",
    "product_id": 82
  }
</code>

Neat, huh? Keep in mind that we're pulling the button up to ''Vcc'', so it's //non-pressed// state reads ''HIGH'', or 1. If we press it and re-run the curl command/paste into a browser, we get back the following:

<code>
$ curl https://api.particle.io/v1/devices/id_here/button?access_token=token_here
{
  "cmd": "VarReturn",
  "name": "button",
  "result": 0,
  "coreInfo": {
    "last_app": "",
    "last_heard": "2016-03-19T20:51:30.817Z",
    "connected": true,
    "last_handshake_at": "2016-03-19T20:32:30.268Z",
    "deviceID": "12345678",
    "product_id": 82
  }
</code>

Note that the contents in ''result'' changed. Since the data is sent in ''json'' format, you can use any number of methods to query the above URL, extract the contents of ''result'', and do something based on that value.

==== Example: getting the brightness from a photoresistor ====

From a code standpoint, this example is nearly identical to the above. The difference is that we will be reading the analog signal from a photoresistor. For some great background information, Adafruit has a [[https://learn.adafruit.com/photocells|nice writeup]] on photoresistors. Here's how we'll wire up our circuit:

[fritzing]

In pictures:

[pic]

**TODO...***
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