Cypher-Plugboard Board (V1.0) Design Specification

Status: Draft Project: Enigma-NG Author: Izzyonstage & GitHub Copilot Version: v.0.1.0 Associated Hardware Revision: Rev A Last Updated: 2026-10-13

Diagrams

• Cypher & Stack Configuration - source: design/Diagrams/cypher-and-stack-configuration-diagrams.drawio

1. Overview

The Cypher-Plugboard Board terminates the Cypher HID interconnect chain beneath whichever board (either Cypher-Input or Cypher-Output, either order) occupies the bottom-most position of the local 2-board HID stack - mirroring the Stack-Blanking Board's end-of-chain role for the 30-rotor mini-stack chain. This specification documents three board variants sharing an identical electrical circuit (HID-chain termination, power passthrough); only the jack field's row count, character layout, and jack quantity differ between them, mirroring the Cypher-Input/Cypher-Output variant split. Variant-specific detail lives in a dedicated document per variant:

• design/Electronics/Cypher-Plugboard/Cypher_Plugboard_26_Char_Design.md
• design/Electronics/Cypher-Plugboard/Cypher_Plugboard_64_Char_Design.md
• design/Electronics/Cypher-Plugboard/Cypher_Plugboard_10_Numeric_Design.md

Electrically, per DEC-088 and DEC-103, this board is deliberately simple: it carries no plugboard-signal-specific pins at all, no BOARD_ROLE_ID strap, and no active components of its own at all - JTAG spoke termination lives on the User Settings Module instead (see User_Settings_Module/Design_Spec.md §4). This board's PCB is a thin strip along the top edge only - just large enough to carry the two interconnect connectors (J1/J2). The physical plugboard patch jacks are not mounted on this PCB at all - they mount directly to a machined metal enclosure that this PCB strip attaches to, and are not electrically connected to this board's own circuitry - each jack terminal is wired via a discrete jumper cable directly back to the Cypher Board's own spade terminal bank (J20+, see Cypher/Design_Spec.md §6), bypassing this board's own PCB and both interconnect connectors entirely. This board's only electrical role is to provide GND continuity and a clean dead-end for every other signal reaching it on either connector (including 3V3_ENIG, which is received but left NC - nothing on this board consumes it).

Circuit Responsibility	Board Role	Key Component
Cypher Left Pair Template mating	Mates the bottom-most HID board's bottom (female) connector, per the shared Cypher Left Pair Template; GND stays fully populated for return-path continuity; every other signal received here (including 3V3_ENIG/5V_MAIN) is left NC (no ENC module, no BOARD_ROLE_ID strap, nothing below this board to relay to)	J1 - Samtec QTS-025 family
User Settings Module Hub mating	Mates USM's own bottom Hub connector; GND stays fully populated for return-path continuity; every other signal received here (including 3V3_ENIG) is left NC (JTAG/I2C termination and relay now live entirely on USM - see User_Settings_Module/Design_Spec.md §4)	J2 - Samtec QTS-025 family
Plugboard jack field (mechanical only, chassis-mounted)	Physical Switchcraft 12A 6.35mm (1/4") switched jack sockets, mounted directly to the machined metal enclosure (not this board's own PCB); wired via harness directly to the Cypher Board's own J20+ spade bank, not through this board's own copper	J3+ (per variant - see each variant's own design file)

Mechanical construction: unlike Cypher-Input/Cypher-Output (which are single PCBs mounting horizontally, stacking vertically on top of the Cypher Board), this board is a hybrid assembly: a small PCB strip (top edge only, carrying J1/J2) attached to a machined metal enclosure that forms the rest of the assembly and hosts the entire jack field. The enclosure is mounted in a vertical orientation, like the Cypher Board itself - so the jack field forms a human-facing front panel with character rows running top-to-bottom, matching the ergonomics of a traditional Enigma plugboard. Each "plug" position is 2 jack sockets (one per plugboard pass) placed immediately next to each other, horizontally (left-to-right) - not stacked vertically - to keep the panel's overall height as small as possible. Rows are stacked vertically below one another, with generous horizontal spacing between adjacent plug-pairs (for tidy patch-cable routing) and generous vertical spacing between rows (so the corresponding character can be engraved/printed on the metal enclosure face directly above each plug-pair - not a PCB silkscreen, since the jack field is not on the PCB). The PCB strip is identical across all three variants (fixed size, independent of jack count - it only ever carries J1/J2). The machined metal enclosure is sized per variant, scaling in height with the row count (see each variant's own design file); the 64-Character variant (the variant with the most rows) is the tallest.

Chassis grounding rationale: mounting the jacks directly to the machined metal enclosure means every jack's metal bushing bonds directly to that enclosure - keeping the entire external jack field on a continuous GND_CHASSIS network, consistent with the rest of the system's external connectors. Per design/Standards/Global_Routing_Spec.md §5, this board's own GND_CHASSIS net (enclosure + jack bushings) is not locally bonded to GND here - it dissipates through the system's single GND_CHASSIS-to-GND bond, which remains on the Power Module only (see §2 GND_CHASSIS Single-Point Bond, below). This is entirely separate from the signal-return GND carried on J1/J2 (see §3), which stays fully populated/continuous on both connectors for return-path integrity, even though almost every other signal reaching this board is left NC.

Open mechanical item: the exact transition between the PCB strip and the machined metal enclosure (fastening method, panel cutout tolerances, cable routing from the PCB strip's J1/J2 down to the jack field) is not yet resolved - deferred to the dedicated mechanical design pass, consistent with the current electronics-only merge scope. The electrical connector definitions below (J1 - Cypher Left Pair Template; J2 - USM Hub Connector Template) are unaffected by this open item.

Functional Requirements

ID	Functional Requirement	Notes	Satisfied By / Cross-Ref
FR-PLB-01	Terminate the Cypher Left Pair Template's dead-end at the bottom of the local 2-board HID stack	GND stays fully populated for return-path continuity; every other signal received at J1 (including 3V3_ENIG/5V_MAIN) is left NC - this board has no ENC module and no BOARD_ROLE_ID strap of its own	§3 Signal Routing; BOM J1
FR-PLB-02	Carry no plugboard-signal-specific pins on either connector	Per DEC-088 - this board's own circuitry never sees plugboard cipher-path signals	§1; §3
FR-PLB-03	Host the physical plugboard jack field on a machined metal enclosure, not this board's own PCB, with no PCB trace connection to this board's own circuitry	Each jack wired via a harness jumper directly to the Cypher Board's own J20+ spade bank	§4 Plugboard Jack Field (Mechanical); BOM J3+ (per variant)
FR-PLB-04	Provide 10 (10-Numeric), 26 (26-Char Classic), or 64 (64-Character) plug positions, each with 2 jack sockets (one per plugboard pass)	Jack count and row layout vary by variant - see each variant's own design file	§4 Plugboard Jack Field (Mechanical)
FR-PLB-05	Connect to whichever HID board occupies the bottom of the local stack, matching the shared Cypher Left Pair Template	J1 = Samtec QTS-025 family (male), mating with that board's bottom (female) connector	§5 Interconnects; BOM J1
FR-PLB-06	Connect to the User Settings Module's bottom Hub connector, relaying nothing further - JTAG/I2C termination lives entirely on USM	J2 = Samtec QTS-025 family (male), mating USM's own bottom (female) Hub connector	§5 Interconnects; BOM J2
FR-PLB-07	Keep the jack field's metal bushings on a continuous GND_CHASSIS network, consistent with the rest of the system's external connectors	Every jack bonds directly to the machined metal enclosure by its threaded bushing; no local GND_CHASSIS-to-GND bond on this board	§2 GND_CHASSIS Single-Point Bond; §4 Plugboard Jack Field (Mechanical)

Design Requirements

ID	Design Requirement	Specification	Satisfied By / Cross-Ref
DR-PLB-01	PCB stackup	4-layer standard per design/Standards/Global_Routing_Spec.md §2.3.1; PCB is a thin strip along the top edge only, carrying J1/J2 only - no active components - identical across all three variants	§6 PCB Fabrication & Stackup
DR-PLB-02	Cypher Left Pair Template connector	J1 (male) = QTS-025-01-L-D-RA-P; mates with whichever HID board's bottom (female, QSS-025-01-L-D-RA-K) connector sits directly above; pin-level template owned by Cypher/Board_Layout.md §4 (its own J5)	§5 Interconnects; BOM J1
DR-PLB-03	USM Hub Connector Template connector	J2 (male) = QTS-025-01-L-D-RA-P; mates USM's own bottom (female, QSS-025-01-L-D-RA-K) Hub connector; pin-level template owned by User_Settings_Module/Board_Layout.md §2	§5 Interconnects; BOM J2
DR-PLB-04	3V3_ENIG/5V_MAIN/BOARD_ROLE_ID_IN[3:0]/BOARD_ROLE_ID_OUT[3:0]/ENC_DATA_IN[5:0]/ENC_DATA_OUT[5:0]/ENC_ACTIVE_INPUT_N/ENC_ACTIVE_OUTPUT_N at J1	All left NC except 3V3_ENIG/5V_MAIN (received, unused) - dead-end signals with nothing below this board to relay to, and this board carries no BOARD_ROLE_ID strap or ENC module of its own	§3 Signal Routing
DR-PLB-05	I2C_SDA/I2C_SCL/TMS/TCK/CPLD_RESET_N/TDI/TDO at J2	All left NC - no I2C device, JTAG TAP, or local logic on this board; USM's own R1-R3 terminate the broadcast JTAG lines, not this board	§3 Signal Routing
DR-PLB-06	3V3_ENIG/GND treatment	3V3_ENIG received at both J1 and J2, left NC at both - no active components remain on this board to bias. GND received at both, kept fully populated/continuous for return-path integrity	§3 Signal Routing
DR-PLB-07	Plugboard jack sockets (per variant)	Switchcraft 12A ("E12A"), 6.35mm (1/4") 2-conductor switched panel-mount phone jack (Tip, Tip-Shunt switch contact, Sleeve); 3/8-32 UNEF-2A threaded bushing, hardware (washer + hex nut) shipped unassembled; mounted directly to the machined metal enclosure (not this board's own PCB); manually assembled, not part of JLCPCB PCBA - no JLCPCB PN; quantity and RefDes range per variant	§4 Plugboard Jack Field (Mechanical); BOM J3+ (per variant)
DR-PLB-08	PCB mounting holes	MH1-MH4: M3 PTH (3.2mm drill) tied to GND_CHASSIS per GRS §4, on the PCB strip only	§6 PCB Fabrication & Stackup
DR-PLB-09	Jack field chassis bonding	Every jack's metal bushing bonds directly to the machined metal enclosure by mechanical contact (threaded bushing through panel cutout + nut) - no additional bonding hardware required. This board's GND_CHASSIS net (enclosure + jack bushings + PCB mounting holes) is not locally bonded to GND - the system's only GND_CHASSIS-to-GND bond remains on the Power Module	§2 GND_CHASSIS Single-Point Bond; §4 Plugboard Jack Field (Mechanical)
DR-PLB-10	ESD protection	Not required on the PCB. J1/J2 are internal BtB connectors, not hot-swapped or externally accessible, per design/Standards/Global_Routing_Spec.md §9. The jack field itself carries no PCB-mounted ESD devices either (it has no PCB trace connection to protect) - patch-cable ESD events are conducted directly to the machined metal enclosure via each jack's chassis bond (DR-PLB-09) rather than into any signal path on this board. Whether any additional protection is needed at the Cypher Board's own J20+ remains an open item, mirroring the equivalent open item already carried there (see Cypher/Design_Spec.md §8)	§7 Thermal & ESD

Component Block Diagram

flowchart TD
  subgraph cypherIface["Cypher Left Pair Template (mates the bottom-most HID board)"]
    J1["J1 male\n3V3_ENIG/5V_MAIN received (NC/unused), GND continuous (return path)\nENC_DATA/ENC_ACTIVE/BOARD_ROLE_ID received (NC - dead-end)"]
  end

  subgraph usmIface["USM Hub Connector Template (mates USM's bottom connector)"]
    J2["J2 male\n3V3_ENIG received (NC/unused), GND continuous (return path)\nI2C_SDA/SCL, TMS/TCK/CPLD_RESET_N, TDI/TDO received (NC - terminated on USM instead)"]
  end

  subgraph jackField["Plugboard Jack Field (machined metal enclosure, not this board's own PCB - no PCB trace connection)"]
    J3["J3+ Switchcraft 12A switched jacks\n(qty/layout per variant)\nmetal bushings bond to enclosure -> GND_CHASSIS"]
  end

  J3 -. "harness jumper (signal), not PCB trace" .-> cypherJ20["Cypher Board J20+ spade bank"]

2. Architecture

• PCB: a thin strip along the top edge only, 4-layer standard per design/Standards/Global_Routing_Spec.md §2.3.1. ENIG Gold. 2.0mm filleted corners. Just large enough to carry J1/J2 - no active components - it does not carry the jack field, which mounts directly to the machined metal enclosure instead (see §4). This PCB strip is identical across all three variants.
• Assembly: Single-sided JLCPCB SMT (rear face only) for J1/J2 - a fully-automated pass, no manual PCBA steps.
• Manufacturer: JLCPCB (standard 4-layer; single-sided SMT PCBA for the PCB strip only). The machined metal enclosure and jack field are a separate mechanical build, not part of the JLCPCB PCBA order.

GND_CHASSIS Single-Point Bond

Per design/Standards/Global_Routing_Spec.md §5: this board's GND_CHASSIS net spans both the PCB strip's own mounting holes and the machined metal enclosure (including every jack's metal bushing, bonded to the enclosure by mechanical contact - see §4). None of this is locally bonded to GND on this assembly. The system's only galvanic GND_CHASSIS-to-GND bond remains on the Power Module.

3. Signal Routing

This board carries no active components and no plugboard-signal-specific pins - every signal reaching either connector other than GND (kept continuous for return-path integrity) is simply left NC, including 3V3_ENIG and (at J1) 5V_MAIN. JTAG spoke termination (TCK/TMS/CPLD_RESET_N) lives entirely on the User Settings Module (R1-R3, see User_Settings_Module/Design_Spec.md §4), not on this board - per DEC-103, J2 mates the User Settings Module directly.

NC / dead-end signals at J1 (Cypher Left Pair Template)

Signal(s)	Reason
5V_MAIN	No LED bank or other 5V_MAIN consumer on this board
ENC_DATA_IN[5:0]/ENC_DATA_OUT[5:0], ENC_ACTIVE_INPUT_N/ENC_ACTIVE_OUTPUT_N	No ENC module on this board; nothing below this board to relay either row to
BOARD_ROLE_ID_IN[3:0]/BOARD_ROLE_ID_OUT[3:0]	This board carries no BOARD_ROLE_ID strap of its own and is not identified by the Cypher Board's compatibility comparator; nothing below this board to relay these bits to

NC / dead-end signals at J2 (USM Hub Connector Template)

Signal(s)	Reason
I2C_SDA/I2C_SCL	No I2C device on this board
TMS/TCK/CPLD_RESET_N	Broadcast JTAG lines, terminated on the User Settings Module itself (R1-R3) - not on this board
TDI/TDO	No JTAG TAP of its own; USM's own Hub Connector Template leaves these NC on its J2 side too (see User_Settings_Module/Board_Layout.md §2)

Continuity signals

Signal(s)	Path
3V3_ENIG (both connectors)	Received at J1 from whichever HID board sits directly above, and at J2 from USM; left NC/unused at both - no active components remain on this board to bias
GND (both connectors)	Received at both; kept fully populated/continuous - not NC, since a continuous signal-return path is required through this board regardless of which other signals are unused

4. Plugboard Jack Field (Mechanical)

The physical plugboard patch jacks mount directly to a machined metal enclosure - not to this board's own PCB - and carry no PCB trace connection to this board's own circuitry (per DEC-088). Each jack terminal is wired via a discrete jumper cable directly back to the Cypher Board's own spade terminal bank (J20+, see Cypher/Design_Spec.md §6).

• Jack type: Switchcraft 12A ("E12A"), 6.35mm (1/4") 2-conductor switched panel-mount phone jack - confirmed 2026-08-19 (datasheet: design/Datasheets/Switchcraft-12A-datasheet.pdf). 3/8-32 UNEF-2A threaded bushing, mounted through a cutout in the machined metal enclosure with the K178 washer and K180 hex nut (hardware shipped unassembled). Manually assembled - not part of the JLCPCB PCBA order, no JLCPCB PN. 3 terminals: Tip, Tip-Shunt (normally-closed switch contact, opens when a plug is inserted), and Sleeve.
• Chassis bonding: each jack's threaded metal bushing makes direct mechanical (and electrical) contact with the machined metal enclosure it mounts through - keeping every jack on a continuous GND_CHASSIS network with the rest of the enclosure and the PCB strip's own mounting holes. No additional bonding hardware is required beyond the jack's own mounting nut. See §2 GND_CHASSIS Single-Point Bond.
• Plug arrangement: each cipher character occupies one "plug" position, consisting of 2 jack sockets placed immediately next to each other, horizontally (left-to-right) - one for each plugboard pass (Pass 1, Pass 2). Positions are not stacked vertically, to keep the enclosure's overall height as small as possible.
• Row layout: character positions are arranged in rows running top-to-bottom on the vertical enclosure face, with the character engraved/printed on the enclosure directly above its plug-pair - not a PCB silkscreen, since the jack field is not on the PCB. Row count and character assignment vary by variant - see each variant's own design file §2.
• Spacing: generous horizontal spacing between adjacent plug-pairs (for tidy patch-cable routing) and generous vertical spacing between rows (for clear per-plug character labelling). Exact dimensions are TBD at mechanical/enclosure layout time.
• Enclosure sizing: the machined metal enclosure is sized per variant, scaling in height with the row count (see each variant's own design file); the PCB strip itself is identical across all three variants (fixed size, independent of jack count - it only ever carries J1/J2).
• Wiring: each jack's Tip and Tip-Shunt terminals are wired together to one spade jumper (matching the historical decode-board terminal role), and the Sleeve terminal to a second spade jumper (matching the historical encode-board terminal role) - both running directly to the corresponding spade terminals on the Cypher Board's J20+ bank - see each variant's own design file for the per-position jack count and the resulting total wire-run count back to J20+.

5. Interconnects

J1 - Cypher Left Pair Template

Pin-level template owned by the Cypher Board (Cypher/Board_Layout.md §4, its own J5) - this board owns only its own physical connector placement and gender, per that shared template.

• MPN: QTS-025-01-L-D-RA-P (Samtec 50-contact 0.635mm right-angle male SMT) - same part as Cypher-Input/Cypher-Output's own J1.
• Mates with: whichever HID board's bottom (female, QSS-025-01-L-D-RA-K) connector sits directly above this board.
• Wiring: 3V3_ENIG received, left NC (no active components remain on this board to bias). GND received, kept fully populated/continuous - not NC, maintains the signal-return path. 5V_MAIN, ENC_DATA_IN[5:0]/ENC_DATA_OUT[5:0], ENC_ACTIVE_INPUT_N/ ENC_ACTIVE_OUTPUT_N, and BOARD_ROLE_ID_IN[3:0]/BOARD_ROLE_ID_OUT[3:0] are all received but left NC on this board - see §3 for the full per-signal rationale.

Pinout: see Board_Layout.md §1 for this board's own wiring; full pin numbering owned by Cypher/Board_Layout.md §4.

J2 - USM Hub Connector Template

Pin-level template owned by the User Settings Module (User_Settings_Module/Board_Layout.md §2, its own J2) - this board owns only its own physical connector placement and gender, per that shared template.

• MPN: QTS-025-01-L-D-RA-P (Samtec 50-contact 0.635mm right-angle male SMT) - same part as this board's own J1.
• Mates with: USM's own bottom (female, QSS-025-01-L-D-RA-K) Hub connector directly above this board, per DEC-103.
• Wiring: 3V3_ENIG received, left NC. GND received, kept fully populated/continuous - not NC, maintains the signal-return path. I2C_SDA/I2C_SCL, TMS/TCK/ CPLD_RESET_N, and TDI/TDO are all received but left NC on this board - no I2C device or JTAG TAP on this board, and USM's own R1-R3 already terminate the broadcast JTAG lines (see §3 for the full per-signal rationale).

Pinout: see Board_Layout.md §2 for this board's own wiring; full pin numbering owned by User_Settings_Module/Board_Layout.md §2.

6. PCB Fabrication & Stackup

• Stackup: 4-layer standard per design/Standards/Global_Routing_Spec.md §2.3.1. This PCB is a thin strip along the top edge only - just large enough for J1/J2, no active components - identical across all three variants; it does not extend down to cover the jack field, which mounts to the separate machined metal enclosure (see §4).
• Manufacturer: JLCPCB. Single-sided SMT PCBA (rear face only) for J1, J2. The machined metal enclosure and jack field are a separate mechanical build, outside the JLCPCB PCBA order.
• Mounting Holes: MH1-MH4, M3 PTH (3.2mm drill), tied to GND_CHASSIS per GRS §4, on the PCB strip itself.

7. Thermal & ESD

• Thermal: No active components. No thermal concerns.
• ESD: J1/J2 are internal BtB connectors, not hot-swapped or externally accessible during normal operation - no TVS/ESD protection required on the PCB strip, per design/Standards/Global_Routing_Spec.md §9. The jack field carries no PCB-mounted ESD devices either, since it has no PCB trace connection at all - patch-cable ESD events are conducted directly to the machined metal enclosure via each jack's chassis bond (§4), not into any signal path on this board. Whether any additional protection is needed at the Cypher Board's own J20+ remains an open item, mirroring the equivalent open item already carried there (see Cypher/Design_Spec.md §8).

8. Branding & Traceability

• Data Plate: Per GRS §6 on Layer L4 (rear face of the PCB strip). Revision block: STECKERBRETT [Cypher-Plugboard] V1.0 (common to all variants; variant-specific suffix TBD - see each variant's own design file).
• Connector Pin-1 Markers: J1/J2 silkscreen pin-1 markers required per GRS §7.1.
• Character labelling: each plug-pair's corresponding character is engraved/printed on the machined metal enclosure directly above that pair - not a PCB silkscreen, since the jack field is not on the PCB - see each variant's own design file for the exact character set and case (26-Char Classic: uppercase only; 64-Character: uppercase row block followed by lowercase row block, per §2 of that variant's own design file).

9. Bill of Materials

This BOM lists only components common to all Plugboard variants (fixed quantity, independent of variant) - the two HID interconnect connectors and the JTAG spoke termination resistors. Variant-specific components (the plugboard jack sockets themselves, RefDes J3+) with their per-variant quantities are listed in each variant's own design file §3 (Cypher_Plugboard_26_Char_Design.md, Cypher_Plugboard_64_Char_Design.md, Cypher_Plugboard_10_Numeric_Design.md).

RefDes	Specification	MPN	Manufacturer	DigiKey PN	Mouser PN	JLCPCB PN	Alt Supplier + PN	Notes	Footprint Available	Footprint Downloaded	Qty
J1, J2	50-contact 0.635mm right-angle male SMT	QTS-025-01-L-D-RA-P	Samtec	QTS-025-01-L-D-RA-P-ND	200-QTS02501LDRAP	C7267889	-	J1: mates with the bottom-most HID board's bottom connector (Cypher Left Pair Template); J2: mates USM's own bottom Hub connector, per DEC-103; same part as Cypher-Input/Cypher-Output J1	✔	✔	2

Sourcing status: J1/J2 have confirmed sourcing, reused directly from Cypher-Input/ Cypher-Output's own already-approved parts. The plugboard jack socket (variant files) is now also confirmed - Switchcraft 12A, DigiKey SC1089-ND, Mouser 502-12A; no JLCPCB PN (manually assembled, not part of the JLCPCB PCBA order) - see each variant's own design file §4 BOM.