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# Quantum Hand-Wiring Guide
Parts list:
* *x* keyswitches (MX, Matias, Gateron, etc)
* *x* diodes
* Keyboard plate (metal, plastic, cardboard, etc)
* Wire (strained for wiring to the Teensy, anything for the rows/columns)
* Soldering iron set at 600ºF or 315ºC (if temperature-controlled)
* Rosin-cored solder (leaded or lead-free)
* Adequate ventilation/a fan
* Tweezers (optional)
* Wire cutters/snippers
## How the Matrix Works (Why We Need Diodes)
The microcontroller (in this case, the Teensy 2.0) 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.
# The Actual Hand-Wiring
## Getting Things in Place
When starting this, you should have all of your stabilisers and keyswitches already installed (and optionally keycaps). If you're using a Cherry-type stabiliser (plate-mounted only, obviously), you'll need to install that before your keyswitches. If you're using Costar ones, you can installed them afterwards.
To make things easier on yourself, make sure all of the keyswitches are oriented the same way (if they can be - not all layouts support this). Despite this, it's important to remember that the contacts on the keyswitches are completely symmetrical. We'll be using the keyswitch's left side contact for wiring the rows, and the right side one for wiring the columns.
Get your soldering iron heated-up and collect the rest of the materials from the part list at the beginning of the guide. Place your keyboard so that the bottoms of the keyswitches are accessible - it may be a good idea to place it on a cloth to protect your keyswitches/keycaps.
Before continuing, plan out where you're going to place your Teensy. If you're working with a board that has a large (6.25u) spacebar, it may be a good idea to place it in-between switches against the plate. Otherwise, you may want to trim some of the leads on the keyswitches where you plan on putting it - this will make it a little harder to solder the wire/diodes, but give you more room to place the Teensy.
## Preparing the Diodes
It's a little easier to solder the diodes in place if you bend them at a 90º angle immediately after the black line - this will help to make sure you put them on the right way (direction matters), and in the correct position. The diodes will look like this when bent (with longer leads):
```
┌─────┬─┐
───┤ │ ├─┐
└─────┴─┘ │
│
```
We'll be using the long lead at the bent end to connect it to the elbow (bent part) of the next diode, creating the row.
## Soldering the Diodes
Starting at the top-left switch, place the diode (with tweezers if you have them) on the switch so that the diode itself is vertically aligned, and the black line is facing toward you. The straight end of the diode should be touching the left contact on the switch, and the bent end should be facing to the right and resting on the switch there, like this:
```
│o
┌┴┐ o
│ │ O
├─┤
└┬┘
└─────────────
```
Letting the diode rest, grab your solder, and touch both it and the soldering iron to the left contact at the same time - the rosin in the solder should make it easy for the solder to flow over both the diode and the keyswitch contact. The diode may move a little, and if it does, carefully position it back it place by grabbing the bent end of the diode - the other end will become hot very quickly. If you find that it's moving too much, using needle-nose pliers of some sort may help to keep the diode still when soldering.
|
