From 9e5e41f071595c14957f091f3f250ca699a08e43 Mon Sep 17 00:00:00 2001 From: mikkeli Date: Thu, 8 Oct 2026 09:24:33 +0900 Subject: [PATCH] Add RTC backup battery to BOM (research pending) The dev kit carrier has pads but no connector populated, so the RTC resets whenever power is removed. Captures the connector part NVIDIA's docs reportedly specify, the community substitute, and the R560 note; battery type and footprint still need checking against the schematic. Co-Authored-By: Claude Opus 5.5 --- docs/BOM.md | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) diff --git a/docs/BOM.md b/docs/BOM.md index fd73007..ab803ae 100644 --- a/docs/BOM.md +++ b/docs/BOM.md @@ -53,3 +53,21 @@ type: reference - M.2 B KEY is **not** mechanically compatible with Mini-PCIe. - Supply voltage should be ~4.0 V for reliable operation. - DO NOT hot-plug while powered. + +## RTC backup battery + +**Status: research pending.** Part choice and footprint not yet verified against NVIDIA's schematic. + +| Field | Value | +|-------|-------| +| **Purpose** | Keep the RTC (`rtc0`, `nvvrs-pseq-rtc`) running while the board is unpowered, so the clock is correct at boot without network or GPS | +| **Carrier board** | P3768 (Orin Nano Developer Kit): pads present, **connector not populated** (needs soldering) | +| **Connector (per NVIDIA docs, as quoted on the forum)** | Wieson AC2651-0011-003-HH, 2-pin, 1.25 mm pitch. A community-used substitute is Molex 53398-0271 header + 51021-0200 housing | +| **Battery** | TBD: coin cell with leads; confirm chemistry/voltage against the carrier board spec (SP-11324-001) | +| **Extra parts** | Forum reports also populating R560 (0.56 Ω, e.g. Panasonic ERJ2BQFR56X); confirm in the P3768 schematic | + +### Notes + +- Without it the clock boots at a stale date (seen 2026-10-08: June 4) until NTP syncs. See the [time sync report](impl/reports/TIME-SYNC.md). +- Forum sources: [RTC battery on Orin Nano DevKit](https://forums.developer.nvidia.com/t/rtc-battery-on-jetson-orin-nano-developer-kit/296732), [How to add RTC battery](https://forums.developer.nvidia.com/t/how-to-add-rtc-battery-in-jetson-orin-nano/255792). +- A reported side effect: the battery lead and socket make the case cover sit unevenly.