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BOM: add Waveshare UPS Power Module (C)

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15-19 V in, 3S 21700 pass-through UPS with an INA219 that the car unit
sees on I2C bus 7 at 0x41 (read-only check: 12.34 V, idle). Bench test
held the Orin >=20 s across a supply swap. Notes the 20 V PD caveat and
the intended ignition-off shutdown via battery current direction.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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mikkeli
2026-10-09 17:04:40 +09:00
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@@ -54,6 +54,28 @@ type: reference
- Supply voltage should be ~4.0 V for reliable operation.
- DO NOT hot-plug while powered.
## Waveshare UPS Power Module (C)
[wiki](https://www.waveshare.com/wiki/UPS_Power_Module_(C))
| Field | Value |
|-------|-------|
| **Purpose** | Keep the Orin running through cranking and short power losses, and give time for a clean shutdown at ignition off |
| **Input** | 15–19 V DC (Waveshare recommends a 19 V / 2.37 A adapter). ⚠ A PD trigger at the standard 20 V level is above the rated maximum |
| **Output** | Input voltage when powered (pass-through); battery voltage (9–12.6 V) when not |
| **Battery** | 3 × 21700 Li-ion in series (not included); charging stops when full and resumes below 12 V |
| **Monitoring** | INA219 on I²C. On the car unit it is **bus 7 (40-pin header), address `0x41`** |
| **Holdover (bench, 2026-10-09)** | ≥ 20 s across a supply swap, enough to ride through cranking |
### Notes
- First read-only check (2026-10-09, on input power, charged): bus 12.34 V, shunt ≈ 0 mV (idle). Chip at power-on defaults (config `0x399f`,
calibration unprogrammed), so read current from the **shunt-voltage register** (0x01, 10 µV/LSB) rather than the current register.
- Ignition-off shutdown (not built yet): on input loss the battery current turns clearly negative (discharging). A small service watches the
INA219, waits out a grace period longer than a crank (30–60 s), then runs `systemctl poweroff`, with low battery voltage as a hard backstop.
The shunt value is unconfirmed; check the schematic before converting shunt mV to amps.
- No GPIO or shutdown signal on the module; the BOOT button may be needed to wake a battery that stopped outputting (FAQ).
## RTC backup battery
**Status: optional, low priority.** Battery choice settled (CR2032); footprint/R560 still to verify against NVIDIA's schematic.