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mikkeli fe284ce540 Plan: ride through cranking, shut down at ignition off

UPS input comes from the ignition-switched socket via a 15 V PD
trigger, so input loss means cranking or ignition off. The INA219
(monitor-only) gives the battery current sign; a host service would mark
cranks, then after a grace period close the recording and power off,
with a voltage floor as backstop. Records the open hardware problem:
after poweroff the UPS keeps the board powered, so it drains and
doesn't auto-start at ignition on.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

2026-10-09 17:10:51 +09:00

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type, status, updated

type	status	updated
plan	active	2026-10-09

Car Power: Ride Through Cranking, Shut Down at Ignition Off

Power chain

cigarette socket (ignition-switched, 65 W class, crank-sensitive)
  → USB-C PD charger → 15 V PD trigger (15 V / 3 A) → DC jack
  → Waveshare UPS Power Module (C), 3S 21700, 15–19 V in, pass-through
  → Orin Nano carrier

Socket power is ignition-switched, so UPS input loss = ignition off or cranking. The UPS rides through cranking (bench: ≥ 20 s holdover across a supply swap). See BOM.

Detection

INA219 on I²C bus 7, 0x41, monitor-only (the UPS has no control lines). Battery current from the shunt-voltage register (0x01, 10 µV/LSB): about 0 or positive (charging) with input present, clearly negative (discharging) when input is lost. Battery voltage (0x02) is the backstop. To confirm on the bench: the sign convention and the discharge magnitude at the Orin's real load (pull the UPS input and read).

Policy (to build)

A small host service polling the INA219 about every 1 s:

State	Condition	Action
on input	current ≥ about 0	nothing
on battery	discharging, < grace	publish `system/power` "on battery"; a short episode that recovers is a crank: stamp it into the recording
ignition off	discharging continuously for grace (start at 60 s; tune after the car crank test)	publish "shutting down" → stop capture (close the session cleanly) → optional parked-at-home step → `systemctl poweroff`
battery low	voltage below a floor (around 10.5 V for 3S, to confirm), at any time	`systemctl poweroff` immediately

Optional parked-at-home step: if home WiFi/LAN is reachable at ignition off, stay up long enough to copy recordings off over the LAN (same LAN-only rule as map sync, project-yukart decision 10), within a hard time cap, then shut down.

Open: getting the Orin back on at ignition on

After poweroff the UPS keeps supplying the board from its battery:

Standby drain: the halted Orin still draws some power, so the pack drains while parked, until the UPS's over-discharge protection cuts out.
No auto-start: the dev kit powers on when power appears. If the UPS output never dropped, ignition on doesn't boot the Orin.

Candidate fixes (hardware, to evaluate):

Cut the UPS output after shutdown (a latching relay or a timer on the output), so the next ignition-on is a real power-up.
Pulse the carrier's power-button header from a small circuit when socket power returns.
Suspend (SC7) instead of poweroff, with wake on a GPIO tied to socket power. Untested on this board, and still drains.

Until this is solved, ignition-off shutdown leaves the car unit off until someone power-cycles it.

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