A button is not the simplest kind of sensor to read. While the concept is simple, there's an interesting subtlety to reading a button. The problem is that buttons bounce: they make some intermittent contact before they make a final, solid connection.
There's a simplistic way to debounce that involves a Busy Waiting design. We'll avoid this and show a somewhat more sophisticated debounce algorithm. As with the LED blinking, we'll rely on the
millis() function to see how long the button has stayed in a given state.
To debounce, we'll need to save the current state of the button. When the button is pressed, the signal on the input pin will become
HIGH and we can save the time at which this leading edge event occurred. ...