Keyboard matrix circuit: Difference between revisions

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

{{Mergeto|Keyboard technology#Keyboard switch matrix|date=November 2008}}

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"/>

Most electronic [[musical keyboard|keyboard]]s used in [[synthesizer]]s, [[electronic organ]]s, and [[digital piano]]s use a '''keyboard matrix circuit''' to connect the switches for each key. In this matrix circuit, the rows and columns are made up of wiring. Depressing a key connects a circuit in the matrix, which causes the tone generation mechanism to be triggered.

==Description==

Without a matrix circuit, a 61-key keyboard wouldfor havea to[[digital havepiano]] 61or wiresa connectedcomputer tokeyboard themight integratedrequire circuit62 ofwires theto keyboard,connect which(one wouldfor beeach an awkwardkey, and a ground)—an awkwardly thick bundle of wiring. With thea matrix circuit, theany entireof 61-key keyboardkeys can sendbe signalsdetermined towith theonly integrated16 circuitwires. withThis twois matricesdrawn ofschematically eightas wiresa thatmatrix areof conceptually arranged into8 columns and 8 rows. Theof electronicwires, orwith digitala switch at every intersection. The keyboard controller scans all of the columns, to determine if a key has been pressed. If a key in the column has been pressed, then the controller scanscans the rows, todetermines determine whichthe row-column hascombination beenat activated. Inwhich a manner analogous to the children's board game "Battleship!", the keyboard controller determines which key has been pressed, and then closesgenerates the switchcode forcorresponding to that key's note. This entire process takes placeoccurs so quickly that the performeruser is not awareunaware of theany 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. ]]

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.

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—greatly improving the performance dynamic of a keyboard.

Matrix circuits for instruments that are intended to be used in a [[monophony|monophonic]] fashion (playing only one note at a time) such as a bass [[pedal keyboard]] are simpler than matrix circuits for instruments that will be used to play [[polyphony|polyphonically]] (multiple notes at once). For keyboards that will be used to play multiple-note chords or multiple-part melodies, the matrix circuit needs to have a diode soldered into the circuit for each key. The [[diode]] acts like a one-way valve in a water plumbing system. Without the diodes, the current would flow "backwards" up the matrix when several keys were pressed at once, which would trigger unwanted notes ("phantom keys") or mask intended notes ([[Keyboard_keys#Control_processor | "phantom key blocking"]).

The second is that instruments with a matrix circuit can only play in a [[Monophony|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]] prevents unwanted notes ("phantom keys") from being triggered, or intended notes from being masked ([[Computer keyboard#Control processor|"phantom key blocking"]]).<ref name="dribin" />

==References==

<references/>

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]].

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>

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>

==See also==

*[[Musical keyboardCharlieplexing]]

*[[Crossbar switch]]

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

*[[CrossbarDiode switchmatrix]]

*[[Polyphony (instrument)]]

==References==

{{Clear}}

{{Reflist|30em}}

[[Category:SynthesizersSynthesizer electronics]]

[[Category:KeyboardsComputer keyboards]]

[[Category:Switches]]