AngloDox Keyboard

This is yet another split keyboard with the following features:

• Per-key RGB LEDs
• Separate function row
• RC-circuit debouncing for each key (the internal pullups allow you to swap switches while the keyboard is on!)
• Kailh hot-swap sockets
• USB-C connectors (but I2C protocol!) for the halves, with ESD protection
• Key polling via shift register instead of matrix
• Entirely manufacturable by JLCPCB, using basic parts as much as possible.

Keyboard Layout

The keyboard layout is specified in keyboard-layout.json and can be edited in KLE. The current layout is based on the reference ANSI-104 layout, with a macro column on the left, a collapsed arrow cluster on the right, and added thumb clusters from the venerable Ergodox keyboard.

The current layout has 46 keys on the left and 54 on the right, for a total of 100 keys.

Development

This relies on a combination of scripts and hand-routing. Here's the general workflow:

1. Generate the basic circuitry as a hierarchical schematic in KiCad.
2. Specify a key layout as a [http://www.keyboard-layout-editor.com/#/](KLE) JSON file.
3. Run the [KLE Placement Plugin](TODO) for the key layout.
4. Specify the layout for each key next to the schematic for the key.
5. Enforce the layout using the [HierarchicalPCB plugin](https://github.com/gauravmm/HierarchicalPcb).
6. Route the parts between keys, using the swap positions option in the KLE Placement Plugin to improve performance.

Regenerate KiCad Library

The Kicad library is generated using JLC2KiCad_lib. To regenerate the library, run:

JLC2KiCadLib C1525 C25779 C36871 C965555 \
    -dir temp_jlc_import/

Then merge the symbol and footprint libraries into the main library manually. Remember to update the Value field of the symbols.

When setting up the Footprint library, set the nickname to footprint.

Design Notes

Component selection is driven by what is available on JLCPCB as a basic part, making construction as cheap as possible. The only extended parts are the USB ESD protection circuit and the RJ11 connectors.

Crystal Design

We choose a generic 12MHz oscillator as it is the cheapest basic part available on LCSC. As the load capacitance is 20pF, and the stray capacitance is assumed to be 5pF, we need a pair of 30pF capacitors to get the right frequency. (See section 3.3 of the application note for the derivation.)

ESD Protection

For peace of mind, we add ESD protection to both USB-C ports.

1. Use a generic bi-directional 6V TVS diode between VBUS and GND.
2. Use a USB-specific ESD protection circuit on the data lines. This is one of the few extended parts we use. This is based on the suggestions in Phil's Lab tutorial.
3. Short shield pins to GND directly. (This disagrees with the tutorial mentioned above.)

Half-to-half Connection

The halves are connected via USB-C to USB-C cables. This is preferable to TRRS cables (which have a nasty habit of shorting connections) and RJ11 cables (which are painfully tall and would have to be hand-soldered later). Since we're already paying the extended part fee for the connector, we might as well use them and enjoy the reversible connection it grants us.

To prevent damage from accidental connections, we apply the same ESD protections to the half-to-half connections as we do to the legitimate USB-C port.