From hospital equipment and engineering controls to telephone systems and household appliances, membrane keyboard are used in a wide variety of applications. At first glance, one might assume that a membrane keyboard is nothing more than a standard keyboard, similar to the type used with computers. While they share some similarities, however, it’s an entirely different type of peripheral with its own characteristics.
With a traditional computer keyboard, the keys are comprised of separate moving parts, independent from each other. A membrane keyboard differs in the sense that it’s a single piece of equipment, with the keys being a part of the entire device. Still confused? Think of it like this: membrane keyboards feature pressure pads on which symbols are printed. When the user presses one of these pads, the pressure is detected; thus, registering the key press. Membrane keyboards deliver a minimal amount of tactile feedback, which allows for easier key presses, although at the cost of lower accuracy.
One of the disadvantages associated with membrane keyboards is the lack of tactile feedback, as noted above. When you press a standard computer keyboard, you can “feel” the button being physically pressed down, at which point you know the key was registered. Membrane keyboards do not offer this same type of feedback, which can make it difficult for users to determine when a press is registered and when it is not.
So, how exactly does a membrane keyboard work? The exact design varies from model to model, but most membrane keyboards rely on an electrical connection between the keyboard and the circuits under which the keys are pressed (see illustration below for an example). In its normal state, the electrical circuit is broken. But when a user presses the key, the top membrane layer is pushed down into the bottom membrane, creating an electrical circuit to register the press.
The illustration above reveals the different layers of a typical membrane keyboard: an upper and bottom membrane layer containing conductive traces, as well as a center layer that’s filled with air or some other type of inert substance. Pressing a key pushes the top membrane layer into the bottom layer to keep the conductive traces flowing. Normally, the switch on a membrane keyboard is lift open, simply because the current cannot cross the gap without the assistance of the upper membrane layer.