Working with Buttons

Arduino: A Quick-Start Guide, Second Edition — by Maik Schmidt (36 / 146)

👈 First Version of a Binary Die | TOC | Adding Your Own Button 👉

In this section you’ll learn how pushbuttons work in principle and how you can use them with an Arduino. We’ll start small and build a circuit that uses a pushbutton to control a single LED.

What exactly is a pushbutton? The following figure shows three views of a typical pushbutton. It has four connectors that fit perfectly on a breadboard (at least after you have straightened them with a pair of pliers). Two opposite pins connect when the button is pushed; otherwise, they are disconnected.

The following picture shows a simple circuit using a pushbutton. Connect pin 7 (chosen completely arbitrarily) to the pushbutton, and connect the pushbutton via a 10kΩ resistor to ground. Then connect the 5-volt power supply to the other pin of the button. Make sure the pushbutton’s orientation is right. Its connected pins have to bridge the gap of the breadboard.

All in all, this approach seems straightforward, but why do we need a resistor again? The problem is that we expect the pushbutton to return a default value (LOW) in case it isn’t pressed. But when the button isn’t pressed, it would be directly connected to ground and would flicker because of static and interference. Only a little bit of current flows through the resistor, and this helps prevent random fluctuations in the voltage at the input pin.

When the button is pressed, there will still be 5 volts at the Arduino’s digital pin, but when the button isn’t pressed, it will cleanly read the connection to ground. We call this a pull-down resistor; a pull-up resistor works exactly the other way around. That is, you have to connect the Arduino’s signal pin to power through the pushbutton and connect the other pin of the pushbutton to ground using a resistor.

Now that we’ve eliminated all this ugly unstable real-world behavior, we can return to the stable and comforting world of software development. The following program checks whether a…

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