Standard keypads allow users to press keys or enter codes to control equipment and machinery. They use several basic switching technologies. Direct membrane keypads consist of a membrane painted with conductive ink, a spacer, and a substrate. Holes punched in the spacer are arranged so that pressing a key deflects the contacts on the membrane to complete the circuit on the substrate. Indirect full-travel membrane keypads mount keys above three layers of punched, flexible polymer sheets that are sandwiched together. Circuits are silk-screened with a conductive silver ink on both the top and bottom membrane layers. A middle spacer separates the two circuits and holes punched in the top spacer are arranged so that pressing a key deflects the top circuit to connect with the bottom circuit. Carbon pill keypads contain protruding, pill-shaped covers that are molded over the top of each key. When a key is pressed, the conductive pill actuates a pad trace. The average life for a carbon pill exceeds 5 million actuations. The contact resistance is usually less than 200 W.
Standard keypads mount on the front or rear of panels and are made from a variety of plastic, thermoplastic, and metallic materials. There are four standard keypad sizes: 1 x 4, 3 x 4, 4 x 4 and 5 x 4. For each keypad size, the first number indicates the number of columns and the second indicates the number of buttons. For example, 1 x 4 keypads have one column and four rows of buttons. 3 x 4 keypads are telephone-style devices with three columns and four rows of buttons. 4 x 4 keypads have four columns and four by rows of buttons. 5 x 4 keypads have five columns and four rows of buttons. Electrical switch specifications for standard keypads include maximum current rating, maximum alternating current (AC) voltage rating, and maximum direct current (DC) current rating. Standard keypads with X-Y outputs are matrix-style devices. Devices with a single pole or common bus outputs require the same number of pins as buttons.
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Grayhill - fully customizable switches, keypads, front panels,... Keypads Front Panels Military Display and Keypad Assemblies Mobile Computers and other Computer Based Products See Grayhill, Inc. Information |
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Crystalfontz: Serial LCD Modules, USB LCD Modules, and... USB LCD Modules with integrated keypads The CFA-635 (20x4) and CFA-631 (20x2), pack the most display area and features possible into the smallest See Crystalfontz America, Inc. Information |
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Universal Serial Bus - Wikipedia, the free encyclopedia In information technology, Universal Serial Bus (USB) is a serial bus standard to interface devices to a host computer. |
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