Page 96 - Programming the Photon Getting Started With the Internet of Things

5

Inputs

In this chapter we will program some input devices such as switches, temperature

sensors, and many more. Input devices are generally used to trigger some output or event.
A simple switch can easily be used to turn something on or off, such as a light-emitting
diode (LED). A sensor used as an input device can be used to monitor something like
temperature or a certain type of gas, and when triggered, it can set a series of events in

motion or just be collected as data and interpreted into something visual. This chapter will
also look at some of the basic programming used in reading and detecting inputs, which
you can use for your own projects in the future. We will look at both digital and analog
inputs, where a digital system will return a value of either 1 or 0 and an analog input will

return a value from 0 to 4095 using some sort of analog-to-digital conversion. In this
chapter you will accomplish the following:

Understand how to read digital and analog inputs

Experiment with using different types of input devices
Learn more about coding with the Particle programming language

Digital Inputs

When we used digitalWrite() in the previous chapter, there were two different states

that the LED could be: either HIGH or LOW. When it comes to using digital inputs, the
same states apply to the switch—it is either HIGH or LOW. When you read the state of a
digital input, it will be connected to either 3V3, which indicates a HIGH state, or to

ground, which indicates a LOW state. By connecting a simple push-button switch to your
Photon, you can easily change the state of a digital input pin by pressing it.

A simple push-button switch as shown in Figure 5.1 is great for experimenting with
digital inputs, and is also an inexpensive component—something to consider when

building your own circuits. You can see it snaps straight into the breadboard on either side
of the gap. This switch is a common component you will become familiar with, as it is
included in almost every electronic starter kit. When looking at the switch in Figure 5.1,
the top two pins are connected together, as are the bottom two pins. When the push-button
switch is pressed down, both sets of pins are connected in a circuit and it becomes

complete.