Getting Started with Arduino

Using a Pushbutton to Control the LED

Blinking an LED was easy, but I don't think you would stay sane if your desk lamp were to continuously blink while you were trying to read a book. Therefore, you need to learn how to control it. In our previous example, the LED was our actuator, and our Arduino was controlling it. What is missing to complete the picture is a sensor.

In this case, we're going to use the simplest form of sensor available: a pushbutton.

If you were to take apart a pushbutton, you would see that it is a very simple device: two bits of metal kept apart by a spring, and a plastic cap that when pressed brings the two bits of metal into contact. When the bits of metal are apart, there is no circulation of current in the pushbutton (a bit like when a water valve is closed); when we press it, we make a connection.

To monitor the state of a switch, there's a new Arduino instruction that you're going to learn: the digitalRead() function.

digitalRead() checks to see whether there is any voltage applied to the pin that you specify between parentheses, and returns a value of HIGH or LOW, depending on its findings. The other instructions that we've used so far haven't returned any information—they just executed what we asked them to do. But that kind of function is a bit limited, because it will force us to stick with very predictable sequences of instructions, with no input from the outside world. With digitalRead(), we can "ask a question" of Arduino and receive an answer that ...