Face-based Time-Tracking on Luckfox Pico

Problem

Industrial site with no stable wifi; legacy fingerprint clocks failed often (wet/dirty hands). 3-5 minute drift per worker per day → painful month-end payroll reconciliation.

Architecture

USB 720p cam → Luckfox Pico (RV1106 NPU 0.5 TOPS) → MTCNN detect (8 ms) → ArcFace embedding INT8 RKNN (220 ms) → cosine match local 1,200-face DB → SQLite log → 4G dongle sync hourly. Tiny 0.96" OLED shows name + time.

Stack & rationale

• Luckfox Pico ($8): 256 MB RAM fits ArcFace INT8 + 1,200-face DB.
• ArcFace over FaceNet: better angular margin for high-FAR tolerance.
• C++ firmware: no Python GC pauses, predictable latency.

Results

• Recognition: 180-280 ms, FAR <0.001 (1,200 faces × 5 angles tested)
• 8 months of continuous run, 0 downtime > 5 min
• ~3 hours/month saved for accounting
• Cost per device: $22 (vs commercial $180+)

Lessons

Low-end NPU is enough for <2000 faces. Lighting consistency matters more than a fancy camera — diffuse LED ring is enough.

Security & Compliance

• Secure boot + signed firmware: only Ed25519-signed binaries can run on the device.
• mTLS between edge and gateway; cert rotation every 90 days.
• No SSH in production firmware — OTA updates only, via signed channel.