BOM Validation Workflow

When a Maker-3D project (embedded controller, audio build, smart-home build) has its component list defined, the typical next step is: create an order list. A frequent failure point: connection parts (cables, connectors, screws), consumables (filament, solder, thermal paste), and existing stock are forgotten. Result: 2-3 deliveries instead of one, plus blocked wait time.

This skill brings a disciplined workflow: extract the BOM, reconcile with the hardware stock, identify missing components CATEGORIZED (main parts, connections, consumables), deliver an order list with estimated prices + sources.

When to use

• A spec note has a component table or list (>5 items)
• Before an order at a parts retailer / Amazon / AliExpress
• During the transition from design phase to build phase (see design-first-iteration + cad-construction)
• When the user asks "can I build this now?" or "what's still missing?"
• Cross-project check: ordering a part useful for multiple projects together

When NOT to use

• Pure software projects with requirements.txt/package.json — other tools
• Schematic reviews without a physical component question (schematic check is separate)
• Projects with 1-2 components — discipline overhead not justified
• The spec note doesn't have a BOM table yet — first finish design, then extract BOM

Workflow (4 phases)

Phase 1: BOM extraction from spec

Read the project spec note and extract ALL components. Pay particular attention to:

• Main parts: microcontrollers, sensors, actuators, displays, batteries
• Structural parts: printed parts (with material + quantity), aluminium profiles, wood
• Connection parts (often forgotten): cables with lengths, connectors (JST/Dupont/XT60), screws (size + length + material), nuts, standoffs
• Consumables: filament quantities (in grams), solder, flux, thermal paste, cable ties, heat-shrink tubing
• Hidden prerequisites: power supply (adapter + plug), tools you don't yet own, programming adapters

Output as a structured table:

| Category | Component | Quantity | Spec | Source in note |
|---|---|---|---|---|
| Main part | ESP32-S3-WROOM-1 | 1 | 16 MB Flash | line 45 |
| Connection | JST-PH 4-pin | 5 | with 200mm cable | line 67 |
| ... | | | | |

Mandatory: every component documented with source line in the spec. If unclear → ask explicitly, don't guess.

Phase 2: Hardware-stock reconciliation

Read the hardware-stock inventory (typically a vault note such as Hardware-Lager.md or an equivalent inventory file).

Per BOM entry: is stock available?

| Component | Required | In stock | Difference | Status |
|---|---|---|---|---|
| ESP32-S3-WROOM-1 | 1 | 3 | +2 | ✓ available |
| JST-PH 4-pin cable | 5 | 0 | -5 | ❌ to order |
| WS2812B LED strip 1m | 1 | 0.5 m | -0.5 m | ❌ to order (or shorten design) |
| M3x10 hex socket | 12 | 50 | +38 | ✓ available |

Important: check not only existence but also sufficient quantity. The user has an installation history in the stock — existing parts may be earmarked for other projects.

Phase 3: Order list with categorization

From the ❌ items: consolidated order list, sorted by source (minimizes shipping costs):

## Order

### Parts retailer (≈ €8-12 shipping)
| Component | Qty | Unit price | Total | Article No |
|---|---|---|---|---|
| JST-PH 4-pin cable 200mm | 5 | €1.20 | €6.00 | JST-PH-4-200 |
| ... | | | | |
| **Sum retailer** | | | **€23.40** | |

### Amazon (often Prime → no shipping)
| ... | | | | |

### AliExpress (long, plan ahead!)
- Delivery time: 2-4 weeks
| ... | | | | |

## Total
- Parts retailer: €23.40
- Amazon: €12.99
- AliExpress: €8.50
- **TOTAL: €44.89** + shipping ≈ €60

Phase 4: Plausibility check + reminder

Before order submit, check explicitly:

1. Are all connection parts included? (cables, connectors, screws)
2. Consumables not forgotten? (filament reserve, solder if needed)
3. Tools? (crimpers, soldering-iron tips)
4. Reserve factor: critical small parts (LEDs, resistors, microcontrollers) always order +1 or +20% — shipping frustration when one breaks
5. Cross-check: other open projects with similar components? Synergy order possible?
6. Finish/material conformity: if the project has a required accent color or material spec, check that stock is on hand before ordering the rest

Output: confirmed order list + update suggestion for hardware stock (what will be earmarked WHEN for WHICH project).

Anti-patterns

• ❌ Ordering on the fly without stock check: leads to duplicate orders, forgotten small parts, blocked wait times
• ❌ Overlooking connection parts: "I probably have the cables somewhere" → at build start they're missing → one-week delay
• ❌ Forgetting consumables: 200g filament reserve missing mid-print → print lost
• ❌ One order per source without synergy check: 4 deliveries instead of 1, €30 shipping burned
• ❌ Not updating hardware stock after order: next session doesn't know what's available
• ❌ Ignoring reserve factor on critical parts: one dead ESP32 without spare = 1 week wait
• ❌ Not checking required accent material stock: the spec'd accent color/material is empty, the build silently defaults to a generic filament → finish drift
• ❌ Omitting BOM source evidence: later it's unclear where which component decision came from

Relation to related topics

• mechanical-design-principles: defines WHICH components even make sense (standard screws vs. odd sizes, snap-fit vs. screws)
• cad-construction: often delivers the spec table from which the BOM is extracted
• design-first-iteration: upstream — BOM validation starts only when design is finished
• A hardware-stock inventory: keep a single source of truth for stock levels (a spreadsheet, a notes file, or a small database) and check the BOM against it before ordering

Real-world impact (projection)

Expected use cases:

• Audio build (planned): >20 components (drivers + amp + housing print parts + wiring + battery) — BOM validation would reduce 2-3 order iterations to 1
• Embedded controller extensions: PT100-sensor extensions, new heating elements — small components often in stock
• Smart-home variant: ESP32-P4 + pool sensors + LCD — mix of stock + order
• Future smart-home builds: typical 5-10 components with high connection-part share

Design note: BOM validation is implemented as a skill rather than a sub-agent — the validation logic needs no tool-restriction overhead, so a skill is the lighter-weight home for it.