abse/museair-usb-assembly

README.md

# MuseAir compact horizontal prototype — sensor under PCB

Replaces the projecting/notched enclosure with one rounded rectangle: 80 × 56 mm footprint, shell 44 mm high, four 3 mm rubber feet. Desk-to-lid height 47 mm; ASK cap adds 0.7 mm. Lid screws sit in shallow counterbores. Existing USB-C socket opens through the right wall; no extension connector or projecting cable bay.

The SEN62 is directly under the PCB, with nominal 4 mm sensor-top to PCB-underside clearance. Air ports face the front horizontally; the sensor GH connector faces upward. The assembly now uses PCB v0.5.6 with the factory-fitted J6 programming socket. All 30 JLC imported component CAD models are used; documented exporter coordinate mirroring is reversed. Official sensor CAD attribution: Sensirion. Supplier model URL/hash provenance: jlc-cad-audit.json.

PCB is mounted to the removable lid on four 6.4 mm standoffs using its unchanged source holes. There are no tall floor posts through the sensor. Lid removal lifts the PCB: disconnect the sensor harness carefully. Viewer lid-off and enclosure-hidden views leave the PCB in its assembled position to show the fit; exploded view is illustrative.

## Prototype assembly

1. Print nonconductive PETG base, lid and carrier. STEP/STL files are in enclosure/. Sensor STEP/STL is a manufacturer reference, not a printable functional sensor. Inspect hole fits, shrinkage, wall finish and clearances before assembly.
2. Carrier support rails are under the sensor with 0.3 mm nominal padding clearance; place compliant insulating pads there. Place 0.4 mm compressed foam pads between carrier and case floor. Mount carrier at X ±18, Y 4 using two nylon M2 × 5 screws; pilot bores 1.6 mm, carrier clearance bores 2.4 mm. Tap plastic as required.
3. Place SEN62 in carrier. Retain with two narrow adjustable nylon straps and compliant padding. CAD strap cylinders illustrate paths, not an exact manufactured strap. Check retention without deformation, excessive load or blocked ports.
4. Fit three individual closed-cell foam seals: 2 mm sensor-to-carrier and 0.5 mm carrier-to-case. Keep ducts isolated from each other and electronics, with no air leakage or constriction. Nominal sensor-face to case-front distance 6.5 mm. Original carrier-derived clear areas: inlets 100.69 / 123.24 mm²; outlet 337.02 mm².
5. Connect genuine JST GH-6 1.25 mm-pitch harness, one-to-one, AWG26, target 80 mm and maximum 100 mm. Cable geometry is illustrative; check mating clearance and bend radius physically.
6. Mount PCB to underside of lid on four source holes with nylon M2 × 8 screws inserted upward. Screw-head envelopes are below the PCB but above the sensor; inspect their clearance. Install ASK plunger and lightpipe. Nominal plunger free gap is 0.45 mm; travel/stop and preload need prototype checks.
7. Attach four Ø8 × 3 mm rubber feet. Close lid using four nylon M2 × 8 screws through 2.4 mm clearance holes and 3.8 mm shallow head counterbores. Connect USB-C 5 V power rated at least 1 A. Opening is 12 × 8.8 mm; choose a plug fitting the roughly 3.2 mm socket setback.

## Programming

Program before fitting the enclosure, or remove the lid to access J6, BOOT and RESET. J6 is a factory-populated JST SH 3-pin, 1.0 mm socket (SM03B-SRSS-TB(LF)(SN), JLCPCB C160403). Use a preterminated straight-through SH3-to-SH3 cable: standard programmer J5 pin 1 TX → J6 pin 1 RX/GPIO20; pin 2 GND → J6 pin 2 GND; pin 3 RX → J6 pin 3 TX/GPIO21. No user soldering. J4 remains optional test pads and is unused for normal programming. Programmer hardware v0.8+ requires UART firmware and 3.3 V logic. Power MuseAir separately through USB-C; leave programmer target power disconnected. Hold BOOT, tap RESET, release BOOT, then flash. Firmware and physical flashing are untested. Current stock for C160403 is unverified.

## Evidence and limits

fit-audit.json records the source poses, aperture areas and 4 mm nominal gap; clearance-checks.json contains exact BREP shell/sensor/carrier/PCB-envelope intersections. Local tscircuit assembly build: 17 records, zero error records; enclosure-free variant has 15 records. Original repository handoff: 159 files retain verified hashes. Local build does not establish new hosted publication.

This compact arrangement removes the former lateral sensor/antenna separation and thermal baffle. The sensor is below the electronics and the antenna region is closer to the sensor housing. Nonconductive shell and fasteners are retained, but physical RF range, temperature offset, humidity response, particulate accuracy, airflow/sealing, power integrity, strap retention, cable mating, controls and stability must be tested before production. CAD cannot establish unchanged measurement quality. Avoid conductive case coatings and retain unrestricted air paths. This is a reviewable prototype.

## Local viewer

Serve this directory with a local HTTP server and open index.html. Use On desk, Remove lid, Hide enclosure, USB access or Exploded buttons. Vendor libraries are included in the zip; no right-click menu is needed.