Membrane Keyboards
A membrane keyboard is one where the keys are not separate, moving parts. These keyboards have outlines and symbols printed on a flat, flexible surface. Membrane keyboards function by electrical contact between the keyboard surface and the underlying circuits when key areas are pressed. Two major benefits of membrane keyboards are that they are very inexpensive to mass produce, and are more resistant against dirt and liquids than most other keyboards.
In general, membrane keyboards consist of three layers. The top and bottom layers contain conductive traces. The center layer, called a spacer, is non-conductive and contains holes wherever a key exists. Its function is to keep the other two layers separate. The key or switch is open because current cannot cross the non-conductive gap. However, when the top layer is pressed down causing it to make contact with the bottom layer, the circuit closes. The conductive traces on the underside of the top layer meet those of the bottom layer, allowing current to flow. This is when a membrane keyboard registers a keystroke.
Membrane keyboards have a variety of applications including PDAs, pocket computing devices, simple handheld calculators, access control systems, remote controls, and similar devices. Typically, they are used in applications where the amount of typing is relatively small or infrequent because most people find typing on them difficult due to the low or non-existent amount of tactile feedback provided.