Cypher-Plugboard Board - 26-Char Classic Variant Design Specification

Status: Draft Project: Enigma-NG Version: v.0.1.0 Associated Hardware Revision: Rev A Last Updated: 2026-08-19 Parent Document: design/Electronics/Cypher-Plugboard/Design_Spec.md

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1. Overview

This document specifies the 26-Char Classic variant of the Enigma-NG Cypher-Plugboard Board. It supports the classic 26-letter cipher alphabet (A-Z, uppercase only), mirroring Cypher-Input's/Cypher-Output's own 26-Char Classic variant character set.

All three Cypher-Plugboard variants share an identical electrical circuit (connector-only HID / USM mating) and an identical PCB strip (J1/J2 only - see design/Electronics/Cypher-Plugboard/Design_Spec.md). Only the jack field's row count, character layout, and jack quantity differ between variants; the jack field mounts to its own machined metal enclosure (not the PCB), sized to this variant's own 3-row layout - it is not sized to the 64-Character variant's taller enclosure, since there is no shared board outline to keep.

2. Jack Field Layout

26 plug positions, each with 2 jack sockets (Pass 1, Pass 2) placed immediately next to each other, horizontally. Arranged in 3 rows, top-to-bottom:

Row	Characters	Positions
1	A B C D E F G H I	9
2	J K L M N O P Q R	9
3	S T U V W X Y Z	8

Total: 26 positions, 52 jack sockets. Unlike the 64-Character variant, there is no extra symbol to append to the shorter third row - this variant's alphabet is exactly 26 letters, so the natural 9/9/8 split is used as-is.

Character order: plain alphabetical order, left-to-right, uppercase only (engraved/printed in capitals on the machined metal enclosure per parent Design_Spec.md §8).

3. RefDes Allocation

Jacks are numbered sequentially, row by row (top-to-bottom), left-to-right within each row, with the Pass 1 jack immediately followed by its Pass 2 partner at each position:

Row	Characters	RefDes Range	Qty
1	A-I	J3-J20	18
2	J-R	J21-J38	18
3	S-Z	J39-J54	16

Total: J3-J54, 52 jack sockets.

4. Bill of Materials

RefDes	Specification	MPN	Manufacturer	DigiKey PN	Mouser PN	JLCPCB PN	Alt Supplier + PN	Notes	Footprint Available	Footprint Downloaded	Qty
J3-J54	Switchcraft 12A ("E12A"), 6.35mm (1/4") 2-conductor switched panel-mount jack	12A	Switchcraft	SC1089-ND	502-12A	-	-	Plugboard patch jacks, 26 positions x 2 passes; manually assembled, not part of the JLCPCB PCBA order (no JLCPCB PN); 3/8-32 UNEF-2A threaded bushing	-	-	52

Sourcing status: confirmed 2026-08-19 - Switchcraft 12A, DigiKey SC1089-ND, Mouser 502-12A. Datasheet: design/Datasheets/Switchcraft-12A-datasheet.pdf.