Page 108 - Programming the Photon Getting Started With the Internet of Things

Const

In our code we introduced a couple of new programming concepts that we can use along

the way. We previously used variables to store our pin numbers in memory; however, in
our firmware we will use something called a constant:

const int POT A0;

This creates a spot of memory just like a variable does for an integer value called POT and
stores the pin value A0. This seems like a variable but it isn’t—when using a constant, you

cannot change or edit the value that is assigned to it, as the name suggests. This can be
useful when you want to store a value in the memory and you know that this value should
never be changed within the code. If you do change your code, then you will receive an

error when verifying your sketch.

map()

Because the returned value of analogRead() is a value between 0 and 4095, you may find

that you need to scale this range of values down into something a bit more manageable. In
our case what we want to do is receive the value from the potentiometer and then write
that value to the LED using analogWrite. Because the analogWrite function has a range

from 0 to 255, we cannot simply write the value of the POT because it would be too high.
For this we can use a function called map() to scale down the values to something we can
use. We can scale the input value using the following code:

int ledval = map(val, 0, 4095, 0, 255);

The map() function is responsible for scaling one set of ranges to another. The input
scale we use is from 0 to 4095, and the output scale is from 0 to 255. If we calculated this
scaling range manually, it would become too complicated and sometimes difficult to work

out; it could also return recurring values of an infinite nature.

The syntax of map() is

map(input, inform, inTo, outFrom, outTo);

The parameters for map() are

input the input value to be scaled

inform the first number in the input scale

inTo the second number in the input scale

outFrom the first number in the output scale

outTo the second number in the output scale