Bill of materials

What it costs

In order

1. Settle the open decisionsFPC pinout reversal safety, op-amp choice, the LDO's height in the board gap, panelization. Two of them change copper, so they come before the board order.
2. Finish EXO-410 routing, then quote both boards6-layer 1.0 mm ENIG at JLCPCB. EXO-410 needs HDI (blind laser vias) and via-in-pad. Panelize 2 × 2: each board is 44.2 mm, under the 70 mm Standard PCBA minimum.
3. Consign the optical sensorsPAT9125EL-TKMT isn't stocked at LCSC. Buy from WPG Americas (MOQ 125) and consign 8 to JLC.
4. Source the op-ampsMCP6V31UT-E/LT through JLC Global Sourcing, or switch to OPA391DCKR (same pinout, stocked).
5. Quote the ball-pinsA bench lot is about 130 pins. The six lengths differ only in the barrel.
6. Buy the mechanical hardwareScrews, spacers, FPC jumpers and PETG (Order D below).
7. Print and assemble the shell34.7 h of printing, 428 g PETG.
8. Bring up two tiles on the benchWithout the hub a tile needs 3.6 V, a 2.048 MHz clock, SYNC and a 3 Mbaud UART on its FPC: a small breakout, a Pico or FTDI cable and a bench supply.
9. Lay out the hubLand patterns, a 72 × 56 mm 4-layer outline, placement and routing. Then the 16-tile order.

Order A · Boards and assembly (JLCPCB)

Gerbers, BOM and pick-and-place files for each board are on the plans page.

EXO-410 contact board

MCP6V31UT-E/LT has only a handful at LCSC: order through Global Sourcing or switch to OPA391DCKR (C2871876). For a full helmet, the DF40 receptacle and the M1.6 nuts need more stock than JLC holds today.

EXO-420 controller board

Order B · Consigned and globally sourced

Order C · Ball-pins (custom)

M1.6x0.35, hex 2.5 A/F, Ø2.0 barrel, Ø1.3 plunger, Ø3.0 ball, 1.5 travel, brass, Au over Ni. The bench tiles can all use one length (EXO-5095), since they don't sit in the shell.

Order D · Hardware and cables

The shell

Ender-3 V3 SE, PETG, 0.4 mm nozzle, 0.2 mm layers, 6 walls, 5 top and bottom layers, 20 % infill, 240/80 °C, brim. The STLs are already in print orientation.

Assembly

1. Remove supports and check every standoff face is flat: it is the board datum.
2. Tap the 48 tile pilots M1.6 and the 4 hub pilots M2, 5–6 mm deep. Heat-set the 4 battery-cover inserts.
3. Glue the front band to the back band with the band tabs, then the crown with the ring tabs. Dry-fit first.
4. On the bench: screw the ball-pins into each contact board's nuts, mate the two boards on their four DF40 pairs, plug the FPC in.
5. Mount the hub first, from inside, on its four standoffs.
6. Mount the tiles from the crown down: FPC out through the tile's slot, a spacer at each hole, M1.6 × 8 from the scalp side between the pins. Snug only.
7. Lay each FPC in its channel, tape every 40 mm or so, over the pod wall and down into the hub.
8. Battery lead into the hub, pouch on a foam pad, cover on. Liner, beanie and retention dial last.

The hub (EXO-430)

Circuit and BOM only so far: no land patterns, outline or routing. Parts come to about $33 a board at JLC library prices.

Open decisions

Still needs a bench: contact impedance and noise on a real head, motion artefacts, pin force and comfort, leakage and fault injection, clock skew over 16 cables, thermal, EMC, gold pin on a tin-plated nut, USB isolation while worn.