[Solved / Archived] Witty Pi 4 Low Voltage Shutdown

How do you power your Witty Pi 4 + RPi 4?

If Witty Pi 4 shuts down your Pi due to low power, its software will write in the log like "Shutting down system because input voltge is too low...", have you saw this message in the log?

If you are powering your Witty Pi + RPi4 via the XH2.54 connector, and the voltage you feed to Witty Pi is too low, your Pi will still be off (ungracefully) even if you have not configured the low-voltage threshold, and you won't see anything in the log.

@admin I'm powering it using the official pi power supply, I've tried two adapters and POE. I get the error hwmon undervoltage detected then it shuts down, so it looks like it's graceful. If I disable the witty pi service then the pi seems to be ok.

Just put a multimeter on it, I'm getting 5.27v on the witty pi when powered off and over 5v when the pi is powered on, so I don't think power is the issue?

I think the undervoltage might be a "false flag", just looking through the log:

[xxxx-xx-xx xx:xx:xx] Witty Pi daemon (v4.14) is started.
[xxxx-xx-xx xx:xx:xx] Running on Raspberry Pi 4 Model B Rev 1.4
[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...
[2024-03-12 10:45:49] Done 🙂
[2024-03-12 10:45:49] Firmware ID: 0x26
[2024-03-12 10:45:49] Firmware Revison: 0x01
[2024-03-12 10:45:49] Current Vout=5.07V, Iout=1.74A
[2024-03-12 10:45:49] System starts up because the button is clicked.
[2024-03-12 10:45:54] Send out the SYS_UP signal via GPIO-17 pin.
[2024-03-12 10:45:54] Pending for incoming shutdown command...
[2024-03-12 10:45:55] Schedule next shutdown at: 2024-03-12 17:30:00
[2024-03-12 10:45:55] Schedule next startup at: 2024-03-13 05:30:00
[2024-03-12 10:45:55] Shutting down system because button is clicked or GPIO-4 is pulled down.
[2024-03-12 10:45:55] Halting all processes and then shutdown Raspberry Pi...

Other than updates I haven't changed anything on the pi, I definitely didn't press the button, so what could pull down GPIO-4?

@msage the log you provided doesn't mention anything about undervoltage. It said the GPIO-4 was pulled down.

Besides human can press the button to pull down GPIO-4, Witty Pi's firmeware may pull down GPIO-4 to emulate button tapping when:

• Scheduled startup/shutdown is due
• In voltage is lower than predefined threshold
• Over-temperature or under-temperature is triggered

For each situation, Witty Pi's firmware write the reason code to the register #11 (I2C_ACTION_REASON), which will be checked after the software detected GPIO-4 has been pulled down.

With that said, if the log says "Shutting down system because button is clicked or GPIO-4 is pulled down", it means:

• GPIO-4 indeed has been pulled down (otherwise you would not see that line in the log)
• Witty Pi's firmware didn't pull down GPIO-4 (otherwise the reason code will be different)

So, it seems either there was other hardware that pull down GPIO-4, or there was strong electromagnetic interference that triggered GPIO-4.

@admin Very, very strange, nothing has changed in my setup and it's been working for months! (other than the bookworm issue). Perhaps I've damaged my witty somehow 🙁

I've just tried it with my witty pi 4 mini that I had spare and it's showing the same problem. Any idea what troubleshooting I could try? I've tried with different power supplies (in case of electromagnetic interference). There is no other hardware other than the pi itself... Could any update have caused it?

Just to add the pi doesn't shut itself down if the witty pi is removed

What happened when you run "sudo shutdown -h now"?

Posted by: @msage

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Just to add the pi doesn't shut itself down if the witty pi is removed

Posted by: @admin

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What happened when you run "sudo shutdown -h now"?

It shutsdown as expected 🙂

I've done some more troubleshooting. I've tried a new bookworm install on a new SD card, I've tried a different pi 4 and the same behaviour is exhibited from the witty pi 4 and witty pi 4 mini 🙁

Do you think it is possible that the MCU (ATtiny841) on your Witty Pi gets reset, and that voltage spike causes the GPIO-4 "pulled down"?  The thoughts come from this topic.

@admin Maybe, but I don't know what would cause it. Would this be an issue for witty pi 4 and the pi 4 mini? As I am seeing the issue with both. EDIT: I've read through the threads and the witty pi 4 (full size) shouldn't be experiencing this issue?

If the enviroment has electromagnetic interference, it could be the case. All Witty Pi boards rely on the internal pull-up resistor and spike filter on the reset pin of ATtiny841, which seems not enough under certain circumstances.