Pull a key off the keyboard and you’ll see roughly how it works. There is a little hole within the plastic base and also the keyboard contains a long round bar with an identical shape. After you press the key, the bar pushes down through the opening to touch the contact layers below. Inside the outlet, there is a little tiny piece of rubber that stops the key from moving down and pushes it copy after you release it. This is often what gives the spring to the keys.
What’s under the keyboard?
Take off the keyboard’s bottom panel and you’ll see how it all works from beneath. The green rectangle at the highest contains three small LEDs that activate the indicator lights for “Num lock”, “Caps lock”, and “Scroll lock”. Notice also the cable running along the within of the case at the highest of the keyboard, which carries electrical signals from the keyboard to your computer’s USB port (or PS/2 port on older machines).
How do the contact layers work?
This is the magic part of a keyboard. The dots you’ll see are places where the keys press the 2 conducting layers together. You’ll see a closeup of the underside of 1 key—and, if you look closely, almost see how it works. The opposite set is on the upper sheet of plastic and printed in dark gray. The 2 sheets are kept apart by a transparent plastic layer except at the holes, which is where the keys knockdown to create the 2 sheets touch.