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{{Short description|Input device}}
{{Use dmy dates|date=September 2023|cs1-dates=y}}
[[File:Telephone-keypad2.svg|thumb|A telephone keypad using the [[ITU E.161]] standard.]]
[[File:Numpad.svg|thumb|Numeric keypad, integrated with a computer keyboard]]
[[
[[File:Window_keypad.jpg|thumb|1984 flier for projected capacitance keypad]]
A '''keypad''' is a block or pad of buttons set with an arrangement of digits, symbols, or alphabetical letters. Pads mostly containing numbers and used with computers are [[numeric keypad]]s. Keypads are found on devices which require mainly numeric input such as [[calculator]]s, [[television remote control|television remote]]s, [[push-button telephone]]s, [[vending machine]]s, [[Automated teller machine|ATM]]s, [[point of sale]] terminals, [[combination lock]]s, [[safe]]s, and [[digital door lock]]s. Many devices follow the [[E.161]] standard for their arrangement.
== Uses and functions ==
A computer keyboard usually
Many [[laptop
▲[[Image:Calculator.kodabar.jpg|thumb|right|120px|A [[calculator]]]]
Keypads for the entry of [[personal identification number|PIN]]s and for product selection appear on many devices including ATMs, vending machines, [[point of sale]] payment devices, time clocks, combination locks and digital door locks.
The keypad of a [[calculator]] contains the digits 0 through 9, together with the four [[arithmetic]] operations, the [[decimal point]] and other more advanced functions.▼
==Keypad technologies==
Apart from mechanical keypads,<ref>{{cite web|url=https://switchandclick.com/best-mechanical-numpads-of-2020/|title=Mechanical keypad|access-date=2023-12-17}}</ref><ref>{{cite web|url=https://voltcave.com/programmable-keypads/|title=Mechanical keypads|access-date=2023-12-17}}</ref><ref>{{cite web|url=https://www.screwfix.com/c/security-ironmongery/mechanical-push-button/cat810342?cm_sp=managedredirect-_-ironmongery-_-pushbuttonlock|title=Mechanical push-button keypad|access-date=2023-12-17}}</ref> there are a wide range of technologies that can be used as keypads, each with distinctive advantages and disadvantages. These include Resistive,<ref>{{cite web|url=https://www.farnell.com/datasheets/523847.pdf|title=Resistive membrane keypad|access-date=2023-12-19}}</ref> Capacitive,<ref>{{cite web|url=https://www.electricity-magnetism.org/capacitive-keypads/|title=Capacitive keypads|access-date=2023-12-17}}</ref> Inductive,<ref>{{cite web|url=https://www.ti.com/lit/ug/tiducr1/tiducr1.pdf?ts=1634269041396&ref_url=https%253A%252F%252Fwww.google.com%252F|title=Inductive keypads|access-date=2023-12-17}}</ref>
Piezoelectric,<ref>{{cite web|url=https://nelson-miller.com/piezo-switches-an-introduction-to-these-touch-switches/|title=Piezo keypads|access-date=2023-12-17}}</ref> and Optical.<ref>{{cite web|url=https://www.ign.com/articles/the-best-optical-keyboards-for-gaming|title=Optical keypads|access-date=2023-12-17}}</ref>
The first key-activated [[mechanical calculator]]s and many [[cash register]]s used "parallel" keys with one column of 0 to 9 for each position the machine could use. A smaller, 10-key input first started on the Standard Adding Machine in 1901.<ref>{{cite web |title=William and Hubert Hopkins machines |url=http://history-computer.com/MechanicalCalculators/20thCentury/Hopkins.html |access-date=2017-07-18}}</ref> The calculator had the digit keys arranged in one row, with zero on the left, and 9 on the right. The modern four-row arrangement debuted with the Sundstrand Adding Machine in 1911.<ref>{{cite web |title=Sundstrand Adding Machine - Underwood Sundstrand |url=http://retrocalculators.com/sundstrand.htm |access-date=2017-07-18}}</ref>
▲
▲== See also ==
The invention of the [[push-button telephone]] keypad is attributed to [[John Karlin|John E. Karlin]], an industrial psychologist at [[Bell Labs]] in Murray Hill, New Jersey.<ref name="NYTObit">{{cite news |title=John E. Karlin, Who Led the Way to All-Digit Dialing, Dies at 94 |date=2013-02-08 |access-date=2013-02-09 |newspaper=[[The New York Times]] |url=https://www.nytimes.com/2013/02/09/business/john-e-karlin-who-led-the-way-to-all-digit-dialing-dies-at-94.html |author-first=Margalit |author-last=Fox}}</ref><ref>{{cite news |title=Monmouth man, inventor of touch-tone keypad, dies at 94 |newspaper=The Star-Ledger |date=2013-02-09 |url=http://www.nj.com/news/index.ssf/2013/02/monmouth_man_inventor_of_touch.html |archive-url=https://web.archive.org/web/20130213085246/http://www.nj.com/news/index.ssf/2013/02/monmouth_man_inventor_of_touch.html |url-status=dead |archive-date=2013-02-13 |access-date=2013-02-09}}</ref> On a [[telephone keypad]], the numbers 1 through 9 are arranged from left to right, top to bottom with 0 in a row below 789 and in the center. Telephone keypads also have the special buttons labelled * ([[asterisk|star]]) and # (octothorpe, [[number sign]], "pound", "hex" or "hash") on either side of the zero key. The keys on a [[telephone]] may also bear letters which have had several auxiliary uses, such as remembering [[area code]]s or whole telephone numbers.
* [[Keyboard]]▼
The layout of calculators and telephone number pads diverged because they developed at around the same time. The phone layout was determined to be fastest by Bell Labs testing for that application, and at the time it controlled all the publicly connected telephones in the United States.
{{further|Telephone keypad#Layout}}
== Origin of the order difference ==
Although calculator keypads pre-date telephone keypads by nearly thirty years, the top-to-bottom order for telephones was the result of research studies conducted by a Bell Labs Human Factors group led by John Karlin. They tested a variety of layouts including a Facit like the two-row arrangement, buttons in a circle, buttons in an arc, and rows of three buttons.<ref name="NYTObit"/> The definitive study was published in 1960: "Human Factor Engineering Studies of the Design and Use of Pushbutton Telephone Sets" by R. L. Deininger.<ref name=":0">{{cite journal |author-last=Deininger |author-first=R. L. |title=Human Factor Engineering Studies of the Design and Use of Pushbutton Telephone Sets |journal=[[The Bell System Technical Journal]] |date=July 1960 |volume=39 |issue= |page=995 |doi=10.1002/j.1538-7305.1960.tb04447.x |url=http://www.ascend.com/bstj/vol39-1960/articles/bstj39-4-995.pdf |access-date=2014-02-07 |archive-url=https://web.archive.org/web/20140124061527/http://www.ascend.com/bstj/vol39-1960/articles/bstj39-4-995.pdf |archive-date=2014-01-24 |url-status=dead}}</ref><ref>{{cite book |author-last=Feldman |author-first=Dave |title=Why Do Clocks Run Clockwise |date=1987 |publisher=Harper & Row |location=New York, USA}}</ref> This study concluded that the adopted layout was best, and that the calculator layout was about 3% slower than the adopted telephone keypad.
Despite the conclusions obtained in the study, there are several popular theories and folk histories explaining the inverse order of telephone and calculator keypads.
* One popular theory suggests that the reason is similar to that given for the QWERTY layout, the unfamiliar ordering slowed users to accommodate the slow switches of the late 1950s and early 1960s.<ref>{{cite web |title=Why is the keypad arrangement different for a telephone and a calculator? |date=2001-05-22 |url=http://www.howstuffworks.com/question641.htm |work=How Stuff Works |access-date=2014-02-07}}</ref>
* Another explanation proposed is that at the time of the introduction of the telephone keypad, telephone numbers in the United States were commonly given out using alphabetical characters for the first two digits. Thus 555-1234 would be given out as KL5-1234. These alpha sequences were mapped to words. "27" was given out as "CRestview", "26" as "ATwood", etc. By placing the "1" key in the upper left, the alphabet was arranged in the normal left-to-right descending order for English characters. Additionally, on a rotary telephone, the "1" hole was at the top, albeit at the top right.
== Keypad track design ==
[[File:Keypad1.png|thumb|Figure 1. Keypad wiring methods: separate connections (left), x/y multiplexing (center), [[Charlieplexing]] (right).]]
=== Separate connections ===
A mechanically-switched 16-key keypad can be connected to a host through 16 separate connecting [[lead (electronics)|lead]]s, plus a [[ground (electricity)|ground]] lead (Figure 1, left). Pressing a key will [[short circuit|short]] to ground, which is detected by the host. This design allows any number or combination of keys can be pressed simultaneously. [[Shift register#Parallel-in serial-out (PISO)|Parallel-in serial-out shift register]]s may be used to [[Shift register#More I/O pins|save I/O pin]]s.
=== X/Y multiplexing ===
{{See also|Keyboard matrix circuit}}
These 16 + 1 leads can be reduced to just 8 by using x/y multiplexing (Figure 1, center). A 16-key keypad uses a 4 × 4 array of 4 I/O lines as outputs and 4 as inputs. A circuit is completed between an output and an input when a key is pressed. Each individual keypress creates a unique signal for the host. If required, and if the processor allows, two keys can be pressed at the same time without ambiguity. Adding [[diode]]s in series with each key prevents [[key ghosting]], allowing multiple simultaneous presses.
=== Charlieplexing ===
{{Main|Charlieplexing}}
8 leads can detect many more keys if [[tri-state multiplexing]] (Figure 1, right) is used instead, which enables (''n''-1) × (''n''/2) keys to be detected with just ''n'' I/O lines. 8 I/O can detect 28 individual keys without ambiguity. Issues can occur with some combinations if two keys are pressed simultaneously. If diodes are used, then the number of unique keys detectable is doubled.<ref>{{cite web |url=https://worldwide.espacenet.com/patent/search/family/054064687/publication/GB2540560A?q=pn%3DGB2540560A |title=Touch sensor |access-date=2023-08-04}}</ref>
==See also==
* [[Arrow keys]]
* [[Charlieplexing]]
* [[Digital door lock]]
* [[Keyboard (computing)]]
* [[Keyboard matrix circuit]]
▲* [[Keyboard technology]]
* [[Key rollover]]
* [[Mobile phone]]
* [[Numeric keypad]]
* [[Push-button telephone]]
* [[Rotary dial]]
* [[Silicone rubber keypad]]
* [[Telephone keypad]]
==References==
{{reflist}}
==External links==
{{Wiktionary|keypad}}
* [http://www.dnatechindia.com/Tutorial/8051-Tutorial/Interfacing-Matrix-Keypad-to-8051.html Interfacing Matrix Keypad to 8051 Controller]
[[Category:Computer
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