Keyboard matrix circuit: Difference between revisions

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{{Short description|Electronics in music and computer keyboards}}

Most electronic [[musical keyboard|keyboard]]s used in [[synthesizer]]s, [[electronic organ]]s, and [[digital piano]]s use a '''keyboard matrix circuit''' in which eight rows and eight columns of wires cross. In this way, 16 wires can provide (8x8) 64 crossings — sufficient for a full five octaves of range (61 notes). By scanning these crossings, a keyboard controller can determine which key was pressed<ref>[http://www.dribin.org/dave/keyboard/one_html/ Dave Dribin: "Keyboard Matrix Help"], (June 24, 2000)</ref>.

A '''keyboard matrix circuit''' is a design used in most electronic [[musical keyboard]]s and [[computer keyboard]]s in which the key switches are connected by a grid of wires, similar to a [[diode matrix]]. For example, 16 wires arranged in 8 rows and 8 columns can connect 64 keys—sufficient for a full five octaves of range (61 notes). By scanning these crossings, a keyboard controller can determine which keys are currently pressed.<ref name="dribin"/>

==Description==

Without a matrix circuit, a 61-key keyboard wouldfor a [[digital piano]] or a computer keyboard might require 62 wires to connect (one for each notekey, and a ground) — an—an awkwardly thick bundle of wiring. With a matrix circuit, any of 61 noteskeys can be determined with only 16 wires. This is drawn schematically as a matrix of 8 columns and 8 rows of wires, with a switch at every intersection. The keyboard controller scans the columns. If a key has been pressed, the controller scans the rows — and in a manner analogous to the board game "Battleship!", the controller determines the row-column combination at which a key has been pressed, and generates athe notecode corresponding to that key. This process occurs so quickly that the performeruser is unaware of any delay.<ref name="dribin">Dave Dribin. [http://www.dribin.org/dave/keyboard/one_html/ "Keyboard Matrix Help"]. 2000.</ref>

[[Image:Inside the Yamaha SY77.jpg|thumb|300px|The inside of a [[Yamaha SY77]] synthesizer shows the various internal components. The switches for each key are connected to the microprocessor chip using a matrix circuit. Even though the SY77 has 61 keys, only atwo small ribbon cablecables of wiring comes from the keyboard matrix. ]]

Dave Dribin.

[http://www.dribin.org/dave/keyboard/one_html/ "Keyboard Matrix Help"]. 2000.

</ref>

[[Image:Inside the Yamaha SY77.jpg|thumb|300px|The inside of a [[Yamaha SY77]] synthesizer shows the various internal components. The switches for each key are connected to the microprocessor chip using a matrix circuit. Even though the SY77 has 61 keys, only a small ribbon cable of wiring comes from the keyboard. ]]

There are at least two limitations with this system. The first is that it provides only a crude binary on/off signal for each key. Better electronic musical keyboards employ two sets of switches for each key that are slightly offset. By determining the timing between the activation of the first and second switches, the velocity of a key press can be determined — greatlydetermined—greatly improving the performance dynamic of a keyboard.

The second is that instruments with a matrix circuit can only play in a [[monophonyMonophony|monophonic]] fashion without the addition of a diode for each key crossing.<ref>Jim Cairns, "Keyboard Encoders" [https://web.archive.org/web/20130708233543/http://www.jimspage.co.nz/encoders.htm jimspage.co.nz]</ref>. The [[diode]] is a one-way valve which prevents unwanted notes ("phantom keys") from being triggered, or intended notes from being masked ([[KeyboardComputer (computing)keyboard#Control_processorControl processor|"phantom key blocking"]]).<ref name="dribin" />

Monophonic instruments and most low-cost computer keyboards reduce costs by leaving out most or all of those diodes. To avoid "phantom keys", the keyboard controller in modern low-cost computer keyboards will ignore further key presses once two keys (other than [[modifier key]]s) have been pressed, which is known as [[rollover (key)#Key jamming and ghosting|key jamming or ghosting]].

To avoid "phantom keys", the keyboard controller in modern low-cost computer keyboards will ignore further key presses once two keys (other than [[modifier key]]s) have been pressed down, which is known as [[rollover (key)#Key jamming and ghosting | jamming]].

In addition to musical keyboards and regular computer keyboards, the matrix circuit approach is also used in [[keypads]] (such as for calculators) and [[pinball]] machines.<ref>Jeff Tyson and Tracy V. Wilson. [http://computer.howstuffworks.com/keyboard2.htm "How Computer Keyboards Work"]</ref><ref>{{cite web |url=http://webpages.charter.net/coinopcauldron/swarticle.html |title=Understanding the Switch Matrix|url-status=dead |archive-url=https://web.archive.org/web/20170611150745/http://webpages.charter.net/coinopcauldron/swarticle.html |archive-date=2017-06-11}}</ref>

The matrix circuit approach used in musical keyboards is also used in other types of non-musical keyboards, such as in the keypads for calculators and the "QWERTY" alphabetic and numeric keyboards used to enter information into computers.<ref>

Jeff Tyson and Tracy V. Wilson.

[http://computer.howstuffworks.com/keyboard2.htm "How Computer Keyboards Work"]

</ref>

The same matrix circuit approach is also used

in many [[pinball]] machines.<ref>

[http://webpages.charter.net/coinopcauldron/swarticle.html "Understanding the Switch Matrix"]

</ref>

Often in pocket calculators the [[multiplexed display#Character-oriented displays|multiplexed digit drive lines]] would be used to scan the keyboard as well, providing further savings.<ref>Stan D’Souza. [http://ww1.microchip.com/downloads/en/appnotes/00529e.pdf "Microchip AN529: Multiplexing LED Drive and a 4x4 Keypad Sampling"]. 1997.</ref>

==References==

<references/>

==See also==

*[[Charlieplexing]]

*[[Crossbar switch]]

*[[Diode matrix]]

*[[Polyphony (instrument)]]

*[[Musical keyboard]]

*[[Keyboard (computing)|Alphanumeric keyboard]] (computing)

*[[Crossbar switch]]

==References==

[[Category:Synthesizers]]

{{Clear}}

{{Reflist|30em}}

[[Category:Synthesizer electronics]]

[[Category:Computer keyboards]]

[[Category:Switches]]