What is a Keyboard Matrix Circuit?

Aug 22, 2017

Unless a computer has a touchscreen interface, it probably supports input through peripherals, the most  common of which is a keyboard. There are several different types of keyboards, including membrane, dome-switch, capacitive, mechanical-switch, buckling-spring, hall-effect, optical and more. Each type has its own unique characteristics. Keyboards used for computers, however, are often designed in a special format known as a matrix circuit. So, what is a keyboard matrix circuit and how does it work exactly?


In the most basic sense, a keyboard matrix circuit is a type of keyboard that features a grid-like array of wires connecting the key switches (hence the name). If the keyboard features 8 rows and 8 columns of wires, for instance, it can support up to 64 keys. The switches are located at the intersection of these wires. Keyboard matrix circuits contain a scanner that’s constantly scanner the grid; thus, allowing it to determine which key is pressed.


If you press the “H” key on a keyboard matrix circuit, for instance, the scanner will notice the switch being activated at the intersection of the wires where the “H” key is located. It’s a fast and accurate process that works well for most keyboards.


The primary benefit of using a matrix circuit design is a reduction of required wires. In keyboards with a matrix circuit, there’s typically a single wire for every key. If the keyboard features 64 keys, for instance, it would need 64 wires.


However, there are also some drawbacks to using keyboard matrix circuits, one of which is its use of binary on and off signals. When compared to other keyboards that use two sets of switches for each key, keyboard matrix circuits have a lower level of performance than their counterpart.


Secondly, keyboard matrix circuits used in musical instructions typically lack diodes at the intersections of the wires. This can result in phantom keys where the keyboard “thinks” a key is pressed when it is really not; thus, increasing the risk of errors.


To recap, keyboard matrix circuits are characterized by the use of a grid-like array of intersecting wires underneath the keys. They feature a sensor that’s specifically used to monitor these wires, which it uses to determine when and where a keypress occurs.

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