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

@admin Incorrect.  It also seems to happen when you have other accessories on the 3.3 volt rail. Regardless, how can I tell if I have the older defective boards or not?

Posted by: @3ricjohanson

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@admin Incorrect.  It also seems to happen when you have other accessories on the 3.3 volt rail. Regardless, how can I tell if I have the older defective boards or not?

What you said has no contradiction with mine. I think I should do some clarifications here.

The root cause of this issue, is the spike on MCU's power rail (3.3V) cause the MCU to reset. The 3.3V is converted from the 5V input voltage. If the 5V input voltage has spike, it will go to 3.3V rail too. The MCU is always powered (even when the Pi is off) and it consumes very small current, also their is no dynamically applied load on 3.3V rail, the spike on 3.3V rail can only come from the 5V input voltage.

When you tap the button to turn on your Pi, the Pi and its accessories are connected to the 5V rail. That means the loads on 5V power supply suddenly increased, and that current is usually higher than the current for normal usage. If the power supply doesn't have the ability to deliver this surge current, there will be a spike on 5V input voltage and that spike also goes to 3.3V rail. Adding additional capacitor is to absorb that spike on 3.3V rail.

If you have other loads apply on 3.3V rails, they will also demand additional current from the 5V power supply, and that increase the chance to meet this issue.

A good power supply can deliver high enough current, or has big decoupling capacitor to absorb the spike. With such power supply this issue will not happen, even using the old revision of Witty Pi 4 Mini.

If you use a power supply that can barely deliver enough current, even the new revision of Witty Pi 4 Mini will suffer the spike and can have the same issue.

How to check if it is new revision of Witty Pi 4 Mini? As mentioned here, newer revision has an additonal capacitor soldered there. If you have the board on hand, you can tell. Checking the photo however is not reliable.

I have this issue with  raspberry zero and witty pi 4 l3v7. It doesn't boot automatically or when pressing the button only when disconnecting the power and reconnecting.

@matthias-goetzke The issue you mentioned is not the same. Witty Pi 4 L3V7 uses Li-Po battery and its power source has no spike, so it is not likely to get the "same" issue on Witty Pi 4 L3V7.

"Doesn't boot automatically" is the result you get, but it doesn't mean it is the same issue. If you keep having such issue, you should open a new thread for that.