The Physics of Keyboards

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    The Anatomy of a Keyboard

    Cody Dianopoulos

    Introduction

    Physics is everywhere: every lightbulb we turn on, every telephone that we use, every timewe get into our car and start the engine. Our ability to conquer physics has set us apartfrom animals and has allowed us to accomplish many incredible feats that, just 100 yearsago, one never wouldve imagined possible.

    The computer is probably the most useful invention for productivity, utilising powerfulcircuitry and computational engines to create an input/output stream. It has several neces-sary components from the tiniest pixels of light that make up the screen to the data storagedevices such as the hard drive.

    The keyboard is a very important component of a computer, as it allows us to actuallyuse the computer. Through a series of keystrokes, we can enter commands as input, driveany of our computational needs, and control the computer to execute what we are lookingto accomplish from the computer. The keyboard is a very complex work of circuitry thatutilises methods that we have studied to make the keyboard functional.

    Basics

    Each key of the keyboard corresponds to a certain ASCII identification. If you hit the ekey, it gets registered by the keyboard, sent to an integrated circuit (IC), gets processed bythe IC, and sent to the computer as a hexadecimal code corresponding to an ASCII character.The certain hexadecimal code that would be sent by the keyboard to the computer as theletter e happens to be 6516. There are 256 different hexadecimal codes that correspond to256 different hexadecimal characters.

    There are several different types of keyboards based on the circuitry that they use. Thereare the membrane, dome-switch, scissor-switch, capacitive, mechanical-switch, buckling-spring, hall-effect, laser, and optical keyboards as the popular ones. In order to make this

    report less than 100 pages, the focus will just be on the membrane keyboard.

    Membrane Keyboard

    The membrane keyboard is currently the most popular keyboard on the market. The follow-ing description is of a standard desktop keyboard. On the surface, there are the keys, whichhave flexible rubber domes attached to them. When one presses the key, the key presses thedome to create contact with the dome and the top membrane layer.

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    The top membrane layer is a layer of vertical circuit paths and nodes. There is a nodefor each of the 109 keys on the keyboard, and each node has its own path to one of 19 pinsthat lead into the IC. Sometimes paths overlap, so new nodes are formed that traverse pathson the other side of the top membrane layer.

    The middle layer is the holes layer. It is made of an insulating plastic material that

    has holes at each node. The holes allow a path between the nodes at the same point on thetop membrane layer and the bottom membrane layer. When no nodes are connected, theholes layer separates the nodes.

    The bottom membrane layer is similar to the top membrane layer. It has nodes at thesame positions as on the top membrane layer, but the circuits consist of horizontal pins thatlead to one of 10 pins that go to the IC.

    When a rubber dome presses a node on the top membrane layer, it comes in contactwith the corresponding node on the bottom membrane layer. One pin is activated on thetop membrane layer, and the corresponding pin is activated on the bottom membrane layer,causing a key press to be registered by the processor. Since there are 19 pins on the topmembrane layer and 10 pins on the bottom membrane layer, there are 19 10 = 190 distinctcombinations that can be formed, which is enough to accommodate for each of the 109 keyson the keyboard.

    Bottom Membrane LayerHoles Layer

    Top Membrane Layer

    Key

    Key Matrix and Graph Theory

    The network of nodes via the top membrane layer, holes layer, and the bottom membranelayer is called the key matrix. The key matrix was designed to ensure that each combinationcorresponds to exactly one key. Without the key matrix, there would be a thick bundle ofwires inside each computer keyboard.

    Each node on the membrane layers is associated with a capacitor in the IC, which isdischarged every time the key is pressed so that a relay of electricity to the capacitor can beformed. The key matrix organises this network of circuits to the IC.

    When more than one key is pressed down, sometimes the keyboard does not type at all.

    With multiple circuits running at once inside the IC at each of the different pins, the ICcannot distinctify one top-bottom combination from another. So often it solves this problemby simply not typing anything.

    The design of the key matrix was an application of graph theory to electrical engineering.It is not simple to design a computer keyboard, as one must accommodate for each of the109 keys. The key matrix started off as a simple 19 10 array, and was transformed intowhat it is now using graph theory and topological manipulations. The design process was

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    not easy, and involved strenuous calculations such the graphs adjacency matrix and turningnumbers.

    Physics

    Keyboards are a prime application of circuitry and electrical engineering to everyday life. Itshard to imagine how much work was behind a keyboard during each use of it. Certain aspectsthat were taught in this course such as resistance (V= IR) and capacitance (Q = CV) wereapplied to the production and design of the keyboard. The processor is an application of datastructures and algorithmic design, and the form of hexadecimal compression was an exampleof using bases from mathematics. But overall, the circuits that comprise the keyboard showexamples of series and parallel capacitors. Each path on each membrane layer is comprisedof multiple nodes in series. Using these concepts from physics, scientists have designed afully operational tool that is used very frequently in modern human life.

    References

    ASCII Table and Description. AsciiTable.com. Ascii Table, n.d. Web. 18 June2013.

    Design Guide - Membrane Switch, Keypad, Membrane Keyboard. YanChuen.com.Yan Chuen Co., LTD, n.d. Web. 18 June 2013.

    Lazaridis, Giorgos. How a Key Matrix Work. PCBHeaven.com. PCB Heaven, 27June 2010. Web. 18 June 2013.

    Mechanical Keyswitches, Membrane Keyswitches, Scissor-Switch Membrane Keyswitches.ErgoCanada.com. Ergo Canada, n.d. Web. 18 June 2013.

    Tyson, Jeff, and Tracy V. Wilson. How Computer Keyboards Work. HowStuff-Works.com. HowStuffWorks, n.d. Web. 18 June 2013.

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