Sourcing: EXO-410 contact board + EXO-420 controller board (JLCPCB 6-layer PCBA)

Research date: 2026-10-27. Nothing was ordered and no supplier was contacted.

Where the numbers come from. LCSC and JLCPCB stock, prices and basic/extended status were read from the JSON endpoints behind their own product pages (wmsc.lcsc.com/ftps/wm/product/detail, jlcpcb.com/api/.../selectSmtComponentList) on the research date. The human-readable pages are https://www.lcsc.com/product-detail/<Cxxxx>.html and https://jlcpcb.com/partdetail/<Cxxxx>. JLC stock is JLC's own assembly stock, separate from LCSC's. Prices are USD, at the quantity bought: 2 tiles = 2 × per-tile quantity, 16 tiles = 16 × per-tile quantity. DigiKey, Mouser and Arrow block automated fetches. Their figures below come from one fetched page (digikey.ca) or from search-engine snapshots, and are marked as such.

Per-tile quantities come from out/pcb/tile_circuit.json, equivalent to what exo.pcb.check writes. check was not run, because it writes under out/pcb/. Note there are 62 op-amps per tile (60 contacts plus UR1 and UR2), not 60. That is 124 for 2 tiles and 992 for a helmet.

Summary: what to change before ordering

Two other notes, not blockers: - The Sinhoo nut is tin-plated and the pin is gold. A gold-to-tin contact at µV signal levels is prone to fretting corrosion. Ask Sinhoo/PEM about a gold-flash or nickel-plated M1.6 SMT nut, or rely on the tin-reflowed nut as the "pad" and accept it. - The 1 µF 6.3 V X5R 0201 coupling capacitors lose roughly half their capacitance at a few volts of DC bias. The 0.07 Hz corner moves to about 0.15 Hz, which is still fine for EEG. Use a 10 V part (C2846675, FH 0201 1 µF 10 V) for margin.

1. MCP6V31U and alternatives (SC70-5, "U" pinout: 1 +IN, 2 V−, 3 −IN, 4 OUT, 5 V+)

1a. MCP6V31UT-E/LT availability

DigiKey and the aggregators list the part as Active. One reseller page says "discontinued", which contradicts the others. DigiKey states a 24-week factory lead time. Microchip's product page refused automated fetches; check it by hand before committing a helmet's worth.

Price at 124 (2 tiles): about CAD 1.94 each at DigiKey (≈ US$1.4; the exchange rate is assumed, not looked up), or $1.61 from LCSC's last 4. At 1,000: about $1.20 (OnlineComponents) to CAD 1.79 (DigiKey reel of 3,000).

1b. Pin-compatible candidates (SC70-5 with the same pinout as MCP6V31U)

Pinouts were checked in each datasheet's pin table. Stock and price are JLC's.

The SGMicro and Gainsil zero-drift parts in stock are SOT-23-5 only. Footprint and pinout differ, so they are not drop-ins.

1c. What the current noise costs (in-band 0.5–100 Hz, follower input behind 200 kΩ plus the contact)

Current noise flows through the source impedance, so it scales with R_source. These are first-order estimates: e_n × √BW, with the OPA391's 1/f term fitted from its 10 Hz and 1 kHz values; i_n × R_s × √BW. Totals add the contact's thermal noise, the 2 × 100 kΩ and the ADS131M08 (0.63 µV in 100 Hz) from docs/pcb.md.

The 5 MΩ case is pessimistic, because a dry contact's impedance is partly capacitive and falls with frequency. Bias current gives I_B × 1.2 MΩ of DC offset: 84 µV for the OPA333, which the AC coupling removes. Chopper input-current spikes into a high-Z source also make intermodulation products, a further point against the 70 pA-class choppers here.

1d. Recommendation

1. Keep MCP6V31UT-E/LT and buy it through JLC Global Sourcing (JLC buys from DigiKey/Mouser/Arrow for the assembly order; https://jlcpcb.com/help/article/60-how-to-use-jlcpcb-global-sourcing-parts-service), or buy it yourself and consign. DigiKey has 8,615, enough for 8 helmets. Expect Global Sourcing markup and 1–2 weeks of lead time.
2. LCSC-stocked alternative: OPA391DCKR (C2871876), not OPA333. Same SC70 pinout, 24 µA, I_B 10 fA, current noise 30 fA/√Hz. It beats the OPA333 at every dry-contact impedance above about 0.4 MΩ and costs about 0.27 µV over the MCP6V31 at 1 MΩ. Its 45 µV offset and 1/f noise below 10 Hz are the trade. JLC holds 1,641, enough for one helmet (992) if bought soon. No footprint change.
3. TLV333IDCKR (C181502, $0.17, 14k in stock) only for a cheap bring-up board, where the noise floor doesn't matter.
4. The comment in circuit.py that OPA333AIDCKR is pin-compatible is correct (TI DCK pin table checked).

2. Specific parts

3. Every BOM line: stock for 2 and 16 tiles, basic vs extended

"Recommended LCSC#" is the code to put in circuit.py. The passives currently have none. ✓ = enough JLC stock for that quantity. Ext = extended (loading fee per unique type), Basic = no fee.

EXO-410 contact board (per tile)

EXO-420 controller board (per tile)

Extended or consigned types: about 15 on EXO-410 (after merging the two 0201 100 nF lines) and 5 on EXO-420. At Standard PCBA's $1.53 per type, that is ≈ $31 per order. The 0201 parts have no basic-library equivalents, so they stay extended.

Existing codes in circuit.py checked: C2928168, C623527, C5215173 (low, wrong reel), C2040, C9002, C7836 (wrong package), C5213732, C44193. All exist.

4. JLCPCB capabilities for this stack

Recommendation. Use JLC06101H-3313 (thin 0.099 mm L1-L2 prepreg, good for the L2 ground under 0201s, no surcharge), or -1080B if you want the thinnest outer prepreg. Use 0.15/0.25 vias only where they sit in 0201 pads. Elsewhere use 0.2/0.3 or larger to stay out of the highest via-fee tier. Consider 0201 pads of 0.35 mm where the placement allows, to get margin on POFV.

Not verified on a JLC page: the dollar surcharge for 0.15 mm drills, any fee for traces under 0.1 mm, the impedance control fee, and the exact 6-layer 1.0 mm board price. JLC's 6-layer page says "5 pcs from $2"; a 2024 post gives ≤ 100 × 100 mm 6-layer at $35.

5. Custom gold-plated spring ball-pins (EXO-5075 … EXO-5125)

Geometry (exo/pcb/pin.py, out/pcb/pins/pins.csv): M1.6 × 0.35 thread 1.4 long, 2.5 A/F hex collar 1.0, Ø2.0 barrel, Ø1.3 plunger, 1.5 travel, Ø3.0 ball. Brass, Au over Ni. Six lengths, 7.5–12.5 mm. Order quantities per helmet: 207 / 362 / 308 / 124 / 39 / 6 (1,046).

Harwin P70 is catalog-only (2.4–8.2 mm, Ø1.5 barrel) and does not fit. Reference prices: OpenBCI dry comb electrodes ≈ $1.50–1.70 each in 30-packs (https://shop.openbci.com/collections/all/eeg).

Recommendation. Send the RFQ to Promax, Richconn and Sandum (closest existing thread: M1.6). Ask whether one barrel plus six plunger or barrel lengths counts as one part for MOQ, since the 4- and 35-per-helmet lengths fail any per-length 1,000 MOQ. Mill-Max only if the Chinese shops fail and the helmet volume justifies 1,000 per length. Budget $0.3–1.0 per pin in production and $1–3 per pin for the 130-pc prototype lot, plus possible setup charges: ≈ $40–400 per helmet. All of this is unverified until quoted.

RFQ text (draft, not sent)

Subject: RFQ – custom threaded ball-head spring contact, 6 lengths

Hello,

We'd like a quote for a custom gold-plated spring contact (dry-electrode EEG headset). STEP files and a drawing are available on request.

Geometry: M1.6×0.35 external thread, 1.4 mm long (screws into an SMT nut); 2.5 mm A/F hex collar, 1.0 mm tall; Ø2.0 mm barrel; Ø1.3 mm plunger, 1.5 mm travel; Ø3.0 mm spherical ball head on the plunger. Lengths (thread shoulder plane to ball centre at mid-travel, +1.5 mm nut): 7.5 / 8.5 / 9.5 / 10.5 / 11.5 / 12.5 mm. Material/plating: brass body and plunger, stainless or music-wire spring; Ni 2–3 µm; hard Au ≥ 0.76 µm on the plunger and ball, Au flash elsewhere. Spring force: 50–150 gf at mid-travel (please propose options).

Quantities (mixed lengths): prototype ≈ 130 pcs; production ≈ 1,046 pcs per set (207/362/308/124/39/6), several sets per year.

Please quote: 1. Unit price per length at 130 / 1,000 / 5,000 pcs 2. MOQ per length, and tooling/NRE/setup charges (can the lengths share one barrel to reduce MOQ?) 3. Sample cost and lead time; production lead time 4. Dimensioned drawing for approval 5. Force-vs-travel curve, contact resistance (mΩ), rated cycles 6. Plating thickness certificate; RoHS/REACH 7. Any existing threaded or ball-head part we could adapt

Thank you, [name, company, address]

6. Estimated cost per tile pair (one EXO-410 + one EXO-420)

Parts only, at JLC library prices for the bought quantity. MCP6V31U through Global Sourcing at ≈ $1.45 (2 tiles) and $1.20 (16 tiles); PAT9125 at $5.64. Pins, PCBs and assembly fees are listed separately.

Order-level PCBA fees (Standard PCBA, estimate from the JLC fee page): two designs, each double-sided: setup 2 × $51.12, stencils 2 × $16.42 → ≈ $135 per order. Extended loading ≈ 20 types × $1.53 ≈ $31. Joints ≈ (1,295 + 176) × $0.0176 ≈ $26 per tile pair. Handling ≥ $15; fixtures ≈ $16. Plus Global Sourcing markup and the consignment fee (≈ $30). 6-layer 1.0 mm ENIG boards: quote needed (from ≈ $35 per 5 pcs ≤ 100 × 100 mm).

Rough order totals, parts plus PCBA fees, before PCBs and pins: - 2 tiles: ≈ $373 + ≈ $280 fees ≈ $650, ≈ $325 per tile pair. - 16 tiles: ≈ $2,575 + ≈ $650 fees ≈ $3,200, ≈ $200 per tile pair.

Add a few percent for JLC attrition.

Proposed circuit.py edits (for whoever owns the board; not applied)

"OPA1":    ..., mpn="MCP6V31UT-E/LT", lcsc="",          # Global Sourcing; LCSC alt: OPA391DCKR C2871876 (same pinout)
"ADS131M08": ..., mpn="ADS131M08IRSNR", lcsc="C5124126",
"FLASH":   ..., mpn="W25Q16JVSNIQ",   lcsc="C2456211",   # 150-mil SOIC-8 matches SOIC-8_3.9x4.9mm
"BUF1G17": ..., mpn="SN74LVC1G17DCKR", lcsc="C10425",   # C7836 is the SOT-23-5 DBV part
"LDO":     ..., mpn="TPS7A2033PDBVR", lcsc="C2862740",   # UL1 only: consider TPS7A2033DQNR C46459900 (1.5 mm stack)
"B2B10R":  ..., mpn="DF40C-10DS-0.4V(58)", lcsc="C6601481",
"B2B10H":  ..., mpn="DF40C-10DP-0.4V(51)", lcsc="C424635",
"PAT9125": ..., mpn="PAT9125EL-TKMT", lcsc="",           # consigned (WPG Americas)
# passives: carry an lcsc per value (see §3); "100k 0.1%" 0201 -> 1 % C106224; "100nF C0G" 0201 -> X7R C22435929

Passing per-instance LCSC numbers for passives means adding an lcsc= argument to Circuit.add, or a value → LCSC table read by check.py when it writes the JLC BOM.