# 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.
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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
| | | |