From bb7623211eb12db18775a9c690433a41793d0ab6 Mon Sep 17 00:00:00 2001 From: Mathieu Moran Date: Sat, 15 Aug 2026 18:46:51 -0400 Subject: [PATCH] docs: add DS3231 RTC to Hardware section (BUG-18) --- PLAN.md | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/PLAN.md b/PLAN.md index 8692b3b..b69fefa 100644 --- a/PLAN.md +++ b/PLAN.md @@ -29,6 +29,13 @@ pick up the project without needing prior chat history. - **Power**: Hard-wired 5V/GND directly to GPIO header (red to Pin 2, black to Pin 6), bypassing the worn micro-USB connector. `vcgencmd get_throttled` returns `0x0` — no undervoltage or throttling. Pi runs at full 1.2 GHz (was ~600 MHz downclocked before the fix). +- **RTC**: **DS3231** module (BUG-18, installed 2026-08-14) on the free I²C bus `i2c-1` — SDA + pin 3, SCL pin 5, VCC pin 1 (3.3V, *not* 5V), GND pin 6. ZS-042 board's charge diode removed + for the non-rechargeable CR2032 backup cell. Enabled via `dtparam=i2c_arm=on` + + `dtoverlay=i2c-rtc,ds3231` in `/boot/firmware/config.txt`, `fake-hwclock` disabled, `i2c-dev` + in `/etc/modules-load.d/i2c-dev.conf`. Probes at `0x68` (driver → `UU` in i2cdetect), 24C32 + EEPROM at `0x57`; power-cycle test boots with the correct time (was `2000-01-01`). SIM868 + HAT's CR1220 also installed and its RTC set via `AT+CCLK` as a secondary backup. - **Car**: 2013 Toyota Yaris. ### SIM868 HAT bring-up notes (important gotchas)