I've built a timelapse camera contraption (4 photos per day) using Witty Pi 4 mini, RPi zero 2 w, Voltaic Power brick, and 5v5w solar panel. After 9 days, it failed to boot the RPi at the scheduled 2025-12-04 8:00 am start-up time. I can see in schedule.log that the startup was scheduled properly on 2025-12-04 at 8:00am. But when I look in wittyPi.log, the "[2025-12-04 08:00:30] Send out the SYS_UP signal via GPIO-17 pin." log entry is not there. Why not? Help! When I went out to check on it, the Witty Pi's white LED was blinking. The Voltaic power brick had all 4 LED's on. The Witty Pi’s 5V to GND solder pads measures 5.17 volts.
the "[2025-12-04 08:00:30] Send out the SYS_UP signal via GPIO-17 pin." log entry is not there
According to the log you provided, it is not just that log entry is missing, your Pi didn't boot up at 2025-12-04 08:00 (there is no log for that session).
The last session is the one at 2025-12-03 15:00, as shown below
[xxxx-xx-xx xx:xx:xx] Witty Pi daemon (v4.21) is started.
[xxxx-xx-xx xx:xx:xx] System: Raspbian GNU/Linux 13 (trixie), Kernel: Linux 6.12.47+rpt-rpi-v7, Architecture: armhf
[xxxx-xx-xx xx:xx:xx] Running on Raspberry Pi Zero 2 W Rev 1.0
[xxxx-xx-xx xx:xx:xx] Witty Pi is not detected, retry in one second...
[xxxx-xx-xx xx:xx:xx] RTC offset register has value 0x78
[xxxx-xx-xx xx:xx:xx] Seems RTC has good time, write RTC time into system
[xxxx-xx-xx xx:xx:xx] Writing RTC time to system...
[2025-12-03 15:30:25] Done :-)
[2025-12-03 15:30:25] Firmware ID: 0x36
[2025-12-03 15:30:25] Firmware Revison: 0x07
[2025-12-03 15:30:25] Current Vout=5.09V, Iout=0.17A
[2025-12-03 15:30:25] System starts up because scheduled startup is due.
[2025-12-03 15:30:30] Send out the SYS_UP signal via GPIO-17 pin.
[2025-12-03 15:30:30] Pending for incoming shutdown command...
[2025-12-03 15:30:31] Schedule next shutdown at: 2025-12-03 15:31:00
[2025-12-03 15:30:31] Schedule next startup at: 2025-12-04 08:00:00
[0:00:32.268253944] [939] [1;32m INFO [1;37mCamera [1;34mcamera_manager.cpp:330 [0mlibcamera v0.5.2+99-bfd68f78
[0:00:32.359608840] [1218] [1;32m INFO [1;37mIPAProxy [1;34mipa_proxy.cpp:180 [0mUsing tuning file /usr/share/libcamera/ipa/rpi/vc4/ov5647.json
[0:00:32.380991392] [1218] [1;32m INFO [1;37mCamera [1;34mcamera_manager.cpp:220 [0mAdding camera '/base/soc/i2c0mux/i2c@1/ov5647@36' for pipeline handler rpi/vc4
[0:00:32.381115350] [1218] [1;32m INFO [1;37mRPI [1;34mvc4.cpp:440 [0mRegistered camera /base/soc/i2c0mux/i2c@1/ov5647@36 to Unicam device /dev/media3 and ISP device /dev/media0
[0:00:32.381179048] [1218] [1;32m INFO [1;37mRPI [1;34mpipeline_base.cpp:1107 [0mUsing configuration file '/usr/share/libcamera/pipeline/rpi/vc4/rpi_apps.yaml'
[0:00:32.404142850] [939] [1;32m INFO [1;37mCamera [1;34mcamera.cpp:1215 [0mconfiguring streams: (0) 800x600-XBGR8888/sRGB (1) 1296x972-SGBRG10_CSI2P/RAW
[0:00:32.405009204] [1218] [1;32m INFO [1;37mRPI [1;34mvc4.cpp:615 [0mSensor: /base/soc/i2c0mux/i2c@1/ov5647@36 - Selected sensor format: 1296x972-SGBRG10_1X10/RAW - Selected unicam format: 1296x972-pGAA/RAW
{'SensorTimestamp': 34398612000, 'ExposureTime': 4702, 'ColourGains': (1.6698964834213257, 1.1816496849060059), 'ColourCorrectionMatrix': (2.111583948135376, -0.5619173049926758, -0.5496702194213867, -0.49196138978004456, 2.0531880855560303, -0.5612230896949768, -0.13735483586788177, -0.5860010981559753, 1.7233459949493408), 'FrameDuration': 21581, 'SensorBlackLevels': (1024, 1024, 1024, 1024), 'AeState': 2, 'DigitalGain': 1.0013755559921265, 'AnalogueGain': 1.0, 'ColourTemperature': 6492, 'Lux': 11280.2001953125, 'FocusFoM': 1178, 'ScalerCrop': (0, 0, 2592, 1944), 'FrameWallClock': 1764797438495299072}
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[2025-12-03 15:30:59] Shutting down system because scheduled shutdown is due.
[2025-12-03 15:30:59] Halting all processes and then shutdown Raspberry Pi...
And it looks normal comparing to the one at 13:00.
Unfortunately, I can not tell what have happened after 2025-12-03 15:30:59, and don't know what the real reason of not booting up the Pi as per schedule.
It may be difficult to troubleshoot an issue like this. However there may be measures you can take to reduce the caused lost. For example, the "guaranteed wake mode", as discussed here: https://www.uugear.com/forums/technial-support-discussion/high-reliability-mode/
The "guaranteed wake mode" is introduced in firmware V7, which is the firmware you are using, so you may turn on this mode (it is off by default). This mode will make sure to boot up your Pi in in given time window, even the scheduling system failed for some reasons. The guaranteed wake gives a chance to automatically resume the device (schedule will be adjusted automatically after the boot). However it only helps when the Pi stays off and missed the scheduled startup (seems to be your case).
Here is my post to explain how to use it: https://www.uugear.com/forums/technial-support-discussion/high-reliability-mode/paged/2/#post-952
In your case, you scheduled 4 startups a day (8:00, 10:30, 13:00 and 15:30). The maximum sleep time for the device is 16.5 hours. If the device sleeps more than 18 hours, you can certainly tell it missed a scheduled already. So you may just run this command to turn on the guaranteed wake mode and it will make sure to wake up your device after approximately 18 hours sleeping:
i2cset -y 0x01 0x08 49 0x12
This may not 100% solve/workaround the problem, because we don't know what actually happened to cause the issue. But if the deivce is sleeping too long and missed the scheduled startup, this is likely to help.
Oh, yay! That's promising. Thank you. I'll certainly give that a try after breakfast.