ADR-121 (Normal Mode) gave us distance and a passable breathing
estimate but couldn't see the heartbeat — cardiac chest displacement
(~0.5 mm) is well below the cm quantisation of `distance:NNN`.
Engineering Mode streams per-range-gate energy at the same 6 Hz
cadence (15 motion + 15 micromotion gates, u32 LE each). The
micromotion bin at the target's distance carries enough cardiac
modulation for FFT peak-detection in the 0.8-2.0 Hz band.
Live result, seated operator ~1.5 m from the radar:
🫁📡 13.0 BPM · 37% норма 12-20
💓📡 76 BPM · 63% норма 60-100
Implementation:
- Send enable-config → set-mode(0x04) → disable-config on startup;
fall back to Normal-Mode ASCII parsing if the sequence fails.
- Binary frame parser: F4 F3 F2 F1 | len(2) | 0x01 | dist(2) | 8z |
motion[15]×u32 LE | micro[15]×u32 LE | F8 F7 F6 F5. Gate the ASCII
line-drain on the engineering_mode flag — first cut ran both
unconditionally and destroyed 80% of partial frames mid-buffer.
- Target-gate selection: distance-bracketed gate first, mid-range
micro-peak fallback, gate 1 default. Per-gate ring buffer of
log-energies feeds a Hann + radix-2 FFT.
- /api/v1/mmwave/vitals now returns real `heart_rate_bpm`.
- raw.html: 💓📡 pill now shows real values (no more "n/a"
placeholder).
- New probe script v2/scripts/probe_ld2402_engineering.py used to
reverse-engineer the wire format; kept in tree for next time.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
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