# Enigma Witness Vault bill of materials
This BOM targets a build-ready $50-$100 commodity Witness Vault. Prices are street estimates in USD and will vary by region, shipping, taxes, header pre-soldering, and whether the buyer already owns cables, fasteners, power supplies, or filament.
Build order:
1. Build the core no-NFC vault first.
2. Add NFC only if the demo needs tap-to-pair or tap-to-open behavior.
3. Do not omit the Pi, microSD, or ATECC608A from the reference design.
## Core no-NFC build
Expected subtotal: **$52-$89**.
| Item | Qty | Estimated unit price | Extended | Source options | Notes |
| --- | ---: | ---: | ---: | --- | --- |
| Raspberry Pi Zero 2 W | 1 | $15-$20 | $15-$20 | Raspberry Pi authorized resellers; Pi Zero 2 W official product page: | Reference host. Prefer the headered version if soldering is a blocker, but budget may rise. |
| 16-32 GB microSD card | 1 | $8-$12 | $8-$12 | SanDisk/Samsung/Kingston retail | Holds OS, Enigma install, local vault bundle, and exports. Use a reputable card. |
| Adafruit ATECC608A STEMMA QT/Qwiic breakout | 1 | $4.95-$6 | $4.95-$6 | Adafruit product 4314: ; DigiKey/Mouser Adafruit channel | Required secure-element sidecar in the reference architecture. Fixed I2C address `0x60`. |
| 0.96 in 128x64 SSD1306 I2C OLED | 1 | $6-$18 | $6-$18 | Commodity SSD1306 modules; Adafruit product 326: | Adafruit STEMMA QT version is easier and pricier; commodity modules are cheaper but may need soldering. Common I2C address `0x3C` or `0x3D`. |
| Short I2C cables or jumper wires | 1 set | $2-$4 | $2-$4 | STEMMA QT/Qwiic cable set, JST-SH pigtails, or Dupont jumpers | Keep leads short. Match the OLED/ATECC connector style. |
| 40-pin male header or pHAT wiring method | 1 | $3-$6 | $3-$6 | Pi header kit, short female jumpers, small perfboard | Needed if using an unpopulated Pi Zero 2 W. Headered Pi may include this cost. |
| M2.5 screws, standoffs, heat-set inserts or printed bosses | 1 set | $4-$8 | $4-$8 | Generic electronics fastener kit | Use non-conductive spacing; avoid metal near the NFC antenna if building the NFC variant later. |
| Micro USB power supply, 5 V class | 1 | $8-$12 | $8-$12 | Raspberry Pi micro USB PSU or reputable 5 V adapter | Do not use mystery power for demos. If a known-good supply is already available, this can be omitted from cash spend. |
| PETG or ASA filament used by enclosure | ~80-150 g | $2-$5 | $2-$5 | Bambu PETG/ASA or reputable 1.75 mm filament | Cost is consumed filament, not a full spool. Avoid conductive/carbon-filled material near antennas. |
### Core budget math
Low commodity path:
```text
Pi Zero 2 W $15
microSD $8
ATECC608A $5
commodity SSD1306 OLED $6
I2C wiring $2
header/wiring $3
fasteners $4
known-good micro USB power $8
filament used $2
-------------------------------
Estimated core subtotal $53
```
Higher convenience path:
```text
Pi Zero 2 W / headered supply choice $20
microSD $12
ATECC608A $5
Adafruit OLED / premium OLED $18
I2C cables $4
header/wiring $6
fastener kit $7
official/reputable power $12
filament used $5
------------------------------------------
Estimated core subtotal $89
```
Procurement target: keep the core cart near **$52-$89** by mixing the official ATECC608A breakout with a commodity OLED and existing known-good power where appropriate. If every convenience option is purchased new, the cart may land slightly above the target before shipping.
## Optional NFC build
Expected additional subtotal with compact commodity PN532: **+$11-$27**.
Expected full subtotal with compact commodity PN532: **$64-$99** if the core build stays disciplined.
| Item | Qty | Estimated unit price | Extended | Source options | Notes |
| --- | ---: | ---: | ---: | --- | --- |
| Compact PN532 NFC module, target envelope 43.6 x 41 x 3.9 mm | 1 | $8-$18 | $8-$18 | Elechouse-style or other compact PN532 modules from electronics distributors/marketplaces; Adafruit PN532 product 364 as a full-size reference: | Use compact module for the package CAD. The Adafruit board is a good reference/dev board but is 51 x 117.7 mm and does not fit the target enclosure without redesign. |
| NFC tags/cards | 2-5 | $2-$6 total | $2-$6 | NTAG213/215 stickers/cards, MIFARE-compatible demo cards | For tap-to-pair, tap-to-open docs, or device-id demo. Do not store secrets on demo tags. |
| Extra wiring or JST cable | 1 | $1-$3 | $1-$3 | Qwiic/STEMMA/Dupont depending on module | Confirm interface and address before final wiring. |
| Longer NFC enclosure filament delta | 1 | $0-$2 | $0-$2 | Same PETG/ASA as core build | The NFC case is 102 mm long instead of 78 mm. |
### NFC budget math
Disciplined NFC path:
```text
Core no-NFC low/mid build $53-$72
compact PN532 module $8-$15
NFC tags/cards $2-$5
extra cable $1-$2
filament delta $0-$2
--------------------------------------
Estimated NFC subtotal $64-$96
```
Premium/full-size development-board path:
```text
Core no-NFC mid/high build $72-$89
Adafruit PN532 reference board $39.95
NFC cards/tags $2-$6
extra wiring $1-$3
case redesign or external mount not budgeted
--------------------------------------------
Estimated premium NFC subtotal $115-$140+
```
The premium/full-size PN532 path is outside the $50-$100 reference package and should be treated as bench development hardware, not the default build.
## What to omit first
Omit in this order when protecting the $50-$100 target:
1. **Optional NFC** — biggest avoidable cost and complexity; use the shorter no-NFC enclosure first.
2. **Premium OLED board** — use a commodity SSD1306 I2C module if soldering is acceptable.
3. **Extra tags/cards** — one reusable tag is enough for a demo.
4. **Convenience cable kits** — use short, clean jumper wiring if budget matters.
5. **Decorative filament or multicolor printing** — print a plain PETG/ASA enclosure first.
6. **Spare fastener assortments** — buy only M2.5 hardware if a lab kit is already available.
7. **New power supply** — only omit from cash spend if a known-good 5 V micro USB supply is already available.
Do **not** omit first:
- Pi Zero 2 W: it is the host that runs the current Enigma local stack.
- microSD: it is the local filesystem and vault bundle storage.
- ATECC608A: it is part of the reference witness identity/key-custody sidecar.
- Safe power: under-voltage produces unreliable demos and can corrupt storage.
## Source and substitution rules
Acceptable substitutions:
- Pi Zero 2 W with or without pre-soldered headers; adjust assembly steps accordingly.
- 16 GB or 32 GB microSD from a reputable brand.
- SSD1306 0.96 in 128x64 I2C OLED at `0x3C`/`0x3D`; prefer modules with mounting holes.
- STEMMA QT/Qwiic wiring or short Dupont jumpers, as long as I2C wiring is clean and strain-relieved.
- PETG or ASA filament; choose PETG for easiest first print and ASA for higher heat resistance.
- Compact PN532 module only for the NFC enclosure.
Avoid:
- Carbon-filled, conductive, metal-filled, or magnetic filament near antennas.
- Oversized NFC boards in the internal NFC CAD variant.
- Mystery microSD cards or under-rated power adapters.
- Storing raw memory plaintext, secrets, or private keys on NFC tags.
- Treating token metadata, NFC taps, QR codes, or product labels as proof of provider deletion or model forgetting.
## Budget variants
| Variant | Includes | Expected subtotal | When to choose |
| --- | --- | ---: | --- |
| Minimum credible core | Pi Zero 2 W, microSD, ATECC608A, commodity OLED, basic wiring, fasteners, known-good power, PETG/ASA print | $52-$60 | First working vault, lab demo, lowest spend. |
| Comfortable core | Core parts with better cables, headered Pi or cleaner wiring, reputable power, nicer fasteners | $65-$89 | Recommended default for reliable demos. |
| Core plus compact NFC | Comfortable core plus compact PN532, one or more tags, NFC enclosure | $76-$99 | Launch/demo build when tap interaction matters. |
| Premium bench NFC | Comfortable core plus full-size Adafruit PN532 dev board | $115-$140+ | Bench testing only; not the reference enclosure budget. |
## Procurement checklist
Before ordering, confirm:
- The Pi is a **Zero 2 W**, not original Zero W.
- Header state matches assembly skill: pre-soldered for speed, unpopulated for lowest height.
- OLED is **I2C SSD1306 128x64** and not SPI-only.
- ATECC608A breakout is the I2C STEMMA QT/Qwiic board with fixed `0x60` address.
- NFC module, if used, fits within the compact 43.6 x 41 x 3.9 mm envelope.
- Fasteners match CAD standoffs/bosses.
- Filament is PETG or ASA, not conductive/carbon-filled.
## Cost boundary language
Use this language externally:
> The reference Enigma Witness Vault is a $50-$100 commodity hardware build. The no-NFC core build is typically around $52-$89 before shipping. Optional compact NFC can keep a disciplined build near $64-$99, while premium full-size NFC development boards are bench accessories and may push the cart above $100.