Keyboard Assembly — Mechanical Design Specification

Status: Draft Project: Enigma-NG Author: Izzyonstage & GitHub Copilot Version: v0.1.0 Associated Hardware Revision: Rev A Last Updated: 2026-04-20

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1. Overview

A standalone operator keyboard assembly using the QWERTY-derived 40-position HID layout to access the machine's 64-character code space. This assembly contains the keyboard panel, the key-switch harness, and one Encoder Module populated/programmed in the KBD_ENC role.

The keyboard assembly is electrically independent of the lightboard assembly. It connects to the Stator through its own 26-pin IDC ribbon on the dedicated KBD_ENC port.

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2. Keyboard Switches

• Keyboard Switches (×40): DPDT 6-pin momentary push-button switches, one per physical HID key position.
  • Mounted in the keyboard panel (mechanical chassis); connect to the KBD_ENC Encoder Module via a field-installable spade-terminal harness.
  • Pole 1 — COM1 + NO1 provides the active-low key path: COM1 -> assigned Encoder input terminal, NO1 -> local GND return. Pressing the key pulls the Encoder input LOW.
  • Pole 2 pins (3×) are unused electrically and may be retained only for mechanical anchoring; no connection to the Encoder electrical netlist.
  • NC1 -> not connected.
  • Part: uxcell-style DPDT 2-pole 6-pin push button switch — purchased from seller gadgetskingdom (eBay item 365271584375, 2 per pack). See design/Datasheets/Gadgetskingdom_DPDT_Keyboard_Switch_Pseudo_Datasheet.md.

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3. Key Panel Layout

The keyboard assembly uses a 40-position physical layout that preserves a conventional QWERTY-inspired operator experience while still exposing the machine's full 64-character logical alphabet.

• Printable key positions (×38): dedicated keycaps for [a-z0-9+=].
• Modifier key positions (×2): one Left Shift key and one Right Shift key.
• Bottom-row arrangement: the two Shift keys flank the bottom row so either hand can access the uppercase alphabetic plane.
• Uppercase behaviour: there are no separate uppercase-only key positions. Holding either Shift key while pressing an alphabetic key yields the corresponding uppercase code (A-Z).

For signal polarity, RC debounce circuit, Schmitt trigger configuration, and Shift key state machine logic, see design/Electronics/Encoder/Design_Spec.md §6 Key Mapping.

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4. Mechanical Key Lever Interface

Each key has a mechanical lever extending downward from the key body to contact the depression bar of the Rotor Actuation Assembly.

See design/Mechanical/Rotor_Actuation_Assembly/Design_Spec.md for the depression bar and pivot lever mechanism that translates keypresses into rotor steps.

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5. Cross-References

Document	Description
design/Electronics/Encoder/Design_Spec.md	Generic Encoder Module pinout, CPLD role definition, key mapping
design/Mechanical/Lightboard_Assembly/Design_Spec.md	Separate but layout-matched lightboard assembly
design/Mechanical/Rotor_Actuation_Assembly/Design_Spec.md	Depression bar, pivot lever, and rotor stepping mechanism