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author	Scott Gorsuch <sgorsuch@gmail.com>	2018-10-23 12:29:35 -0400
committer	Drashna Jaelre <drashna@live.com>	2018-10-23 09:29:35 -0700
commit	572c316e7dfb0bcd495ce09e068078593fd4ec82 (patch)
tree	7a1551755892b2577a412edd17ebfc586316221d /lib/lufa/Projects/AVRISP-MKII/Lib/V2ProtocolParams.h
parent	cb1e45b4efdc685134c0dbc35100e2fb99c5b006 (diff)
download	firmware-572c316e7dfb0bcd495ce09e068078593fd4ec82.tar.gz firmware-572c316e7dfb0bcd495ce09e068078593fd4ec82.tar.bz2 firmware-572c316e7dfb0bcd495ce09e068078593fd4ec82.zip

Keymap: Fix missing 4 key (#4219)

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# Hand-Wiring Guide

## Preamble: How a Keyboard Matrix Works (and why we need diodes)

The collapsible section below covers why keyboards are wired the way they are, as outlined in this guide.  It isn't required reading to make your own hand wired keyboard, but provides background information.

<details>

<summary>Click for details</summary>

Without a matrix circuit each switch would require its own wire directly to the controller.

Simply put, when the circuit is arranged in rows and columns, if a key is pressed, a column wire makes contact with a row wire and completes a circuit. The keyboard controller detects this closed circuit and registers it as a key press.

The microcontroller will be setup up via the firmware to send a logical 1 to the columns, one at a time, and read from the rows, all at once - this process is called matrix scanning. The matrix is a bunch of open switches that, by default, don't allow any current to pass through - the firmware will read this as no keys being pressed. As soon as you press one key down, the logical 1 that was coming from the column the keyswitch is attached to gets passed through the switch and to the corresponding row - check out the following 2x2 example:

        Column 0 being scanned     Column 1 being scanned
                  x                                   x
                 col0     col1              col0     col1
                  |        |                 |        |
        row0 ---(key0)---(key1)    row0 ---(key0)---(key1)
                  |        |                 |        |
        row1 ---(key2)---(key3)    row1 ---(key2)---(key3)

The `x` represents that the column/row associated has a value of 1, or is HIGH. Here, we see that no keys are being pressed, so no rows get an `x`. For one keyswitch, keep in mind that one side of the contacts is connected to its row, and the other, its column.

When we press `key0`, `col0` gets connected to `row0`, so the values that the firmware receives for that row is `0b01` (the `0b` here means that this is a bit value, meaning all of the following digits are bits - 0 or 1 - and represent the keys in that column). We'll use this notation to show when a keyswitch has been pressed, to show that the column and row are being connected:

        Column 0 being scanned     Column 1 being scanned
                  x                                   x
                 col0     col1              col0     col1
                  |        |                 |        |
      x row0 ---(-+-0)---(key1)    row0 ---(-+-0)---(key1)
                  |        |                 |        |
        row1 ---(key2)---(key3)    row1 ---(key2)---(key3)

We can now see that `row0` has an `x`, so has the value of 1. As a whole, the data the firmware receives when `key0` is pressed is

    col0: 0b01
    col1: 0b00
            │└row0
            └row1

A problem arises when you start pressing more than one key at a time. Looking at our matrix again, it should become pretty obvious:

        Column 0 being scanned     Column 1 being scanned
                  x                                   x
                 col0     col1              col0     col1
                  |        |                 |        |
      x row0 ---(-+-0)---(-+-1)  x row0 ---(-+-0)---(-+-1)
                  |        |                 |        |
      x row1 ---(key2)---(-+-3)  x row1 ---(key2)---(-+-3)

      Remember that this ^ is still connected to row1

The data we get from that is:

    col0: 0b11
    col1: 0b11
            │└row0
            └row1

Which isn't accurate, since we only have 3 keys pressed down, not all 4. This behavior is called ghosting, and only happens in odd scenarios like this, but can be much more common on a bigger keyboard. The way we can get around this is by placing a diode after the keyswitch, but before it connects to its row. A diode only allows current to pass through one way, which will protect our other columns/rows from being activated in the previous example. We'll represent a dioded matrix like this;

        Column 0 being scanned     Column 1 being scanned
                    x                                   x
                  col0      col1              col0     col1
                    │        │                 |        │
                 (key0)   (key1)            (key0)   (key1)
                  ! │      ! │               ! |      ! │
        row0 ─────┴────────┘ │     row0 ─────┴────────┘ │
                    │        │                 |        │
                 (key2)   (key3)            (key2)   (key3)
                  !        !                 !        !
        row1 ─────┴────────┘       row1 ─────┴────────┘

In practical applications, the black line of the diode will be placed facing the row, and away from the keyswitch - the `!` in this case is the diode, where the gap represents the black line. A good way to remember this is to think of this symbol: `>|`

Now when we press the three keys, invoking what would be a ghosting scenario:

        Column 0 being scanned     Column 1 being scanned
                    x                                   x
                  col0      col1              col0     col1
                    │        │                 │        │
                 (┌─┤0)   (┌─┤1)            (┌─┤0)   (┌─┤1)
                  ! │      ! │               ! │      ! │
      x row0 ─────┴────────┘ │   x row0 ─────┴────────┘ │
                    │        │                 │        │
                 (key2)   (┌─┘3)            (key2)   (┌─┘3)
                  !        !                 !        !
        row1 ─────┴────────┘     x row1 ─────┴────────┘

Things act as they should! Which will get us the following data:

    col0: 0b01
    col1: 0b11
            │└row0
            └row1

The firmware can then use this correct data to detect what it should do, and eventually, what signals it needs to send to the OS.

Further reading:
- [Wikipedia article](https://en.wikipedia.org/wiki/Keyboard_matrix_circuit)
- [Deskthority article](https://deskthority.net/wiki/Keyboard_matrix)
- [Keyboard Matrix Help by Dave Dribin (2000)](https://www.dribin.org/dave/keyboard/one_html/)
- [How Key Matrices Works by PCBheaven](http://pcbheaven.com/wikipages/How_Key_Matrices_Works/) (animated examples)
- [How keyboards work - QMK documentation](how_keyboards_work.md)

</details>


## Parts list

You will need: (where *x* is the number of keys on your planned keyboard)

* QMK compatible microcontroller board (Teensy, Pro-Micro, QMK Proton C etc.)
* *x* keyswitches (MX, Matias, Gateron, etc)
* *x* through hole diodes
* Keyboard plate and plate mount stabilisers
* Wire
* Soldering iron
* Rosin-cored solder
* Adequate ventilation/a fan
* Wire cutters/snippers

Optional but useful:

* Wire strippers/a sharp knife
* Tweezers and/or small needle nose pliers
* Soldering station/Helping hands

## Starting the build

There are many ways to hand wire a PCB matrix, this guide will describe the fundamentals as well as some recommended ways to go about it.

As we are dealing with hand wiring, it is assumed that you already have a plate.  If you are planning a completely custom layout, tools such as [ai03 Plate Generator](https://kbplate.ai03.me/) and [Swillkb Plate & Case Builder](http://builder.swillkb.com/) can help when designing one.

Start by installing the switches and stabilisers in the plate. Depending on the thickness and material this may also involve hot gluing it in place.

## Planning the matrix

If you are following a pre-existing handwire guide (e.g. for the keyboards in the [handwire firmware section](https://github.com/qmk/qmk_firmware/tree/master/keyboards/handwired) you can skip this step, just ensure you wire the matrix as described.

What you want to achieve is one leg from each switch being attached to the corresponding switches next to it (rows) and the other leg being attached to the switches above and below it (columns) and a diode to one of the legs, mosy commonly this will be the leg attached to the rows, and the diode will face away from it (Column to Row) i.e. with the wire furthest from the black line on the diode connected to the switch (as current will only travel in one direction through a diode)


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