[Solved / Archived] Witty Pi 4 Mini: Tapping the On/Off switch doesn't turn on the Raspberry Pi

It seems the MCU (ATtiny841) on Witty Pi 4 Mini got reset when you tap the button. We have observed similar issue when the power supply was not stable enough, or there were electromagnetic interference sources nearby. As far as we know, this issue has chance to happen on Raspberry Pi B models, and we have not seen it happen on Raspberry Pi Zero models.

Do you have a capacitor (10uF or higher)? If you do, you may connect the capacitor between 3V3 and GND (as shown in the picture attached), and usually it will stabilise the 3.3 voltage and avoid this kind of issue.

Thanks you very much 🙂

I connected the 10uF capacity and it works now.

Hello there 🙂

I seem to have a similar issue with my WittyPi 4 mini with Pi Zero W which turns on most of the times without problem but sometimes it (unpredictably) doesnt. This is the case with both turning it on manually with the button as well as the automatic startup with a schedule. Do you think this could be the same issue or have an idea what else could cause this? When I cant turn it on manually it sometimes helps to unplug it and plug it back in later, however as i need to run my project remotely in the future without being able to access it for several months this is not a real solution. I use an original Raspberry Pi power supply which should provide stable 5.2 Volts, the only reason i could think of is if my USB accessories (a 4G network card) would draw to much current at startup, however it doesnt make sense to me that it just sometimes doesnt work. Unfortunately I dont have a capacitor at hand at the moment, do you have any other idea in the meantime on how to fix this or additional information about the other cases where this occurred?

Thank you for your help!

@uugear Any updates on the topic? I have since tested the fix with the capactior and it seems to work fine so far with my testing systems. However since it is planned to make several more of those systems in the future which need to run reliably additional information would really be helpful to know the root cause of the problem. My power supply doesnt seem to be the problem and i can't really imagine it is caused by electromagnetic interference. My best guess at the moment would be that it is a combination with a high initial power draw of the 4G-Modem and an issue with the capacitor of the MCU.

I'm having the same issue as @Eagleshot on my Pi Zero W. It just doesn't want to turn on unless I kill the power completely for a short period of time.

It's definitely the Witty Pi 4 Mini board: as I have the same power supply/battery pack setup remotely with a Witty Pi 3 Mini without issue.

@eagleshot the reason of this issue is most probably because the input voltage drops too much when the MCU decides to power your Pi (connects a load to the power rails), the voltage that powers the MCU itself also drops accordingly and sometimes the MCU will get reset because of low voltage powering. Connecting a capacitor between 3.3V and GND will help stablizing the voltage for MCU.

The newer revision of Witty Pi 4 Mini already has that additional capacitor on board.

@spknmmike If you are using power bank, then most probably it was not the same issue.

If the white LED on Witty Pi 4 Mini doesn't blink at all, that means your power bank automatically enters sleep mode and stop powering Witty Pi 4 Mini + Raspberry Pi. In such case you may try turning on the dummy load, but there is no guarantee that it will work with every power bank.

Posted by: @admin

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@spknmmike If you are using power bank, then most probably it was not the same issue.

If the white LED on Witty Pi 4 Mini doesn't blink at all, that means your power bank automatically enters sleep mode and stop powering Witty Pi 4 Mini + Raspberry Pi. In such case you may try turning on the dummy load, but there is no guarantee that it will work with every power bank.

I'm using Voltaic's V25 "always on" power banks for both Witty Pi 3 Mini and 4 Mini. Both are atop of a Pi Zero W.

I only have the issue on the Witty Pi 4 Mini.

Where/when is the newer revision available? I just bought mine a couple weeks ago from Adafruit.

We put the newer revision in our e-shop since March 2023, however our distributors may or may not have the new revision.

Posted by: @admin

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We put the newer revision in our e-shop since March 2023, however our distributors may or may not have the new revision.

Hi there, 

I landed here because I'm having the same problem on several of my boards. 

How can I tell if I have the newer revision of the board which fixes this problem? 

A power management board which can't turn on is frustrating!  If the supply is good enough for the PI, it should be good enough for the RTC board.  

Best, 

-3ric

@admin Do you know if the normal Witty Pi 4 is also affected by this issue at all? I also think that with the amount of people that have the same issue in this forum it would probably be good to at least update the user manual to include this issue for troubleshooting.

Posted by: @eagleshot

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Do you know if the normal Witty Pi 4 is also affected by this issue at all?

The full-sized Witty Pi 4 doesn't have this issue. The old revision of Witty Pi 4 Mini does not always have this issue. This issue could happen on old Witty Pi 4 Mini when the power supply is not stable enough.

Perfect, thank you for the quick reply!

just for the records, I'm having the same bogus behaviour on my wittypi 4 mini / raspberry pi zero WH. It's definitely not the power source nor garbled EM nearby.