Page 126 - Programming the Photon Getting Started With the Internet of Things

The program starts with a basic variable, which will be used to return a value when the
webpage requests the function on the Photon board. The other variable is used to identify
the analog pin that we are going to use to read from a sensor or similar device, in this case

analog pin A0. In the setup function we link the two variables together using
spark.variable. The first parameter is always the name given to the variable (analog),
and the second parameter identifies the variable that the sensor is connected to on the
Photon board (getvalue), and finally the last parameter defines the type of value, which

is an integer value.

Upload the program to the Photon board to test it out. You can do this using the Web
browser, because unlike functions, variables use HTTP GET requests, which can you can

easily issue using the uniform resource locator (URL) in your browser. So with this in
mind open up a browser and type the following URL into it:

https://api.spark.io/v1/devices/<device ID>/analog?access_token=<Access tok
en>

The request page should look like something Figure 6.7.

Figure 6.7 URL request in browser.

You can reload the page a few times, which will resend the URL request to the Photon,

and you should see a different value. Currently, as there is nothing connecting to the
analog pin, the value is floating.

Reading a Light Sensor

In this experiment we are going to be using a simple photoresistor to measure light levels
and display that information on a webpage with a nice interface that should look similar to
Figure 6.8.