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JESK56

The JESK56 is a diodeless 56-key ortholinear keyboard, using a single QMK-compatible RP2040-based microcontroller. The JESK56 utilises a new type of circuit design stemming from graph theory and mathematical design theory. All previous diodeless keyboards on the market have at most 21 keys per microcontroller. So all such keyboards must be split into two halves to function as a regular keyboard, and must use two microcontrollers over the two halves. This makes the JESK56 the first non-split diodeless keyboard.

Due to its diodeless-ness, the JESK56 is ideal for the custom keyboard community, as it reduces the cost and complexity of making a custom mechanical keyboard.

Why 'JESK'?

Typical mechanical keyboards arrange their keys in a grid pattern. In such a grid, there are cycles of four keys. If no diodes were used and three keys of a four-key cycle were pressed, the keyboard would act like all four keys were being pressed. See https://pcbheaven.com/wikipages/How_Key_Matrices_Works/ for an explainer of this phenomenon. By adding a diode to every key, the keyboard becomes "n-key-rollover", meaning that the keyboard can theoretically distinguish all combinations of keypresses. In software, however, 6-key rollover is typically used, meaning the software assumes that if more than six keys are being pressed, then keys were pressed on accident. Common standards are 2-key-rollover (such as in membrane keybards), 6-key-rollover (mechanical/gaming keyboards), and n-key-rollover (where all combinations of keypresses are distinguished). These are often written as 2KRO, 6KRO, and NKRO. The JESK56 obtains 4-key-rollover, although the board has been specifically designed to function as a n-key-rollover in almost all practical situations.

In graph theory, it is possible to make graphs that do not contain small cycles. Each graph can be converted into a new type of key matrix, with differing characteristics. A recent paper studied graphs of high algebraic connectivity; see Attainable bounds for algebraic connectivity and maximally-connected regular graphs. They found a graph of girth 6 (no 3-, 4-, or 5-cycles) with 28 vertices and 56 edges. JESK is an acronym of the four authors' surnames: Janssen, Exoo, Salamon, and Kolokolnikov.

For more details on this graph, see House of Graphs. This converts to a key matrix with just a 4-key rollover (4KRO). However, by designing the board specifically, all problematic 5-key and 6-key sequences may be practically eliminated. When each finger uses one column (or half a row for the thumb keys), the JESK56 will have NKRO as long as you do not press two pairs of keys (4 keys) with each pair of keysactivated using the same finger (i.e. in the same coloumn/thumb row).

This design is powered using an RP2040-powered microcontroller with 28 pins. I suggest the 16M version of the following: See https://www.aliexpress.com/item/1005006130019224.html

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