Acoustic Drone Sensor Hardware Prototype

Must be U.S. based.

Project Title: Acoustic Drone-Detection Sensor Prototype Assembly — 5-Mic Array, Solar/LTE, IP65 Enclosure
Project Overview:
We need a skilled hardware prototyper to source parts, 3D print components, fabricate, wire, and assemble one complete acoustic drone-detection sensor unit from our finalized design package (parts list, wiring diagram, and mechanical layout provided). This is a build-to-spec job, not a from-scratch design job — we have a working prototype already; we need a second unit built to match it exactly (or you may be iterating on unit #2/3 for a small batch, depending on how the engagement goes).
Budget:
Parts budget: not to exceed $350 (reimbursed against itemized receipts — our internal reconciled BOM cost is ~$264/unit, so this leaves headroom for retail-vs-bulk pricing differences)
Labor budget: not to exceed $400, fixed-price for the full build (sourcing, printing, wiring, bring-up, assembly, and testing)
Bids above either cap should be justified in the proposal; we're open to discussing if your quote is close but reasoned.
Scope — Parts Sourcing:
You will source and purchase all parts (~19 line items) and bill us for cost, within the parts budget above — full BOM with reference pricing and supplier suggestions will be shared with the awarded freelancer, including:
Raspberry Pi 4 Model B (main controller)
1x waterproof USB MEMS microphone (primary)
4x SPH0645LM4H I2S MEMS mic breakouts, arranged N/S/E/W
CN3791 MPPT solar charge controller
3.2V 10Ah LiFePO4 cell
Waveshare SIM7600G-H 4G HAT (LTE connectivity)
Polycarbonate NEMA 65 enclosure (10×8×4 in / 250×115×200mm)
Cable glands, brass standoffs, SMA antenna bulkhead
STL files for 8x 3D-printed mounts/brackets (PETG): heat spreader, acoustic dampening baffle, solar controller standoff, connectivity module mount, primary mic mount, and 4x individual I2S mic mounts (N/S/E/W)
Please itemize parts costs separately from labor in your bid so we can track BOM cost against our internal budget.
Scope — 3D Printing:
You will print all 8 mounts/brackets in PETG on your own equipment. STL files and material spec (infill percentages vary by part — from 20% for lightweight standoffs to 100% for the thermal heat spreader) will be provided.
Wiring (diagram provided):
Power path: LiFePO4 cell → CN3791 MPPT charger (solar in on PV_IN) → regulated output feeds Pi 4 (5V), 4G HAT (5V), and primary USB mic (5V via USB bus). Pi 4 steps down to 3.3V for the four I2S mic breakouts.
Data path: Pi 4 I2S bus → 4x SPH0645LM4H breakouts (BCLK, WS, DOUT, 3.3V, GND each); Pi 4 USB → primary mic + 4G HAT data; Pi 4 UART/GPIO → 4G HAT modem control.
Mechanical:
Component layout and assembly hierarchy provided (not yet fabrication-ready CAD — you'll be working from a component-placement model, so some fit-up judgment is expected). Enclosure is a fixed NEMA polycarbonate box; all internal mounts are 3D-printed PETG per the STL files provided.
Assembly Phases (we'll provide the full step-by-step, this is the summary):
Source & Fabricate — purchase all parts, print all 8 mounts/brackets, drill enclosure for cable glands + SMA passthrough, test-fit standoffs
Wire — solder power distribution harness (battery → charger → controller), wire the 4-mic I2S array, terminate USB/LTE connections, continuity-check all rails
Bring-up — verify 3.3V/5V rail stability under load, confirm I2S devices are detected by the system, validate LTE signal, calibrate beamforming phase alignment across the plus-array
Assemble — mount electronics + heat spreader, secure the acoustic baffle/mic array, install glands and seal for IP65, final power-on + connectivity test
Deliverables:
One fully assembled, tested acoustic sensor unit matching the provided spec
Itemized parts receipts/invoices for reimbursement
Photos/video of each assembly phase for our QA records
Confirmation of successful bring-up tests (rail voltages, mic detection, LTE connectivity, beamforming calibration)
Notes on any deviations from spec, part substitutions, or fit issues encountered (since the mechanical model isn't fabrication-ready CAD, some field adjustment is expected — document it)
Tools/Skills Required:
Own 3D printer calibrated for PETG
Fine-tip soldering, wire stripping/crimping, M3/M2.5 hex drivers
Comfortable with I2S and USB differential signaling
Experience with Raspberry Pi GPIO/peripheral bring-up
Drill + stepped bit for cable gland penetrations
Multimeter for rail verification
Reliable parts-sourcing channels (DigiKey, Mouser, Amazon, etc.) and ability to front costs before reimbursement, or invoice-then-pay arrangement (open to discussing)
Nice to Have:
Prior beamforming/microphone-array phase-alignment experience
Experience sealing enclosures to IP65 spec
Project Type: Fixed-price for labor (cap $400), plus reimbursed parts cost (cap $350, itemized separately). Single-unit build with possible follow-on units if this goes well. Full parts list, wiring diagram, and assembly instructions provided upon award. Please share any past acoustic/embedded hardware assembly work with your bid, and confirm your preferred parts-cost reimbursement method (upfront budget cap + receipts, or invoice-then-reimburse).