Hi.
I have a pi acting as part of infrastructure that can have little to no downtime.
In the event of a power outage or glitch that causes my pi to turn off, what are some methods of remote boot I could consider.
Is there an established and easy WOL guide? Can the pi boot itself?
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Hey there, @Pixmusix,
As far as I’m aware there is no native method on the Raspberry Pi for rebooting after a power outage, it does not even come with Wake-On-LAN capability.
I’m wondering if you couldn’t set up the Pico, or another microcontroller, to read a semi-continuous serial connection from the Pi and if it ever fails, the Pico can turn it back on.
My two ideas for this:
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You put an always on relay that the Pico controls, sending power to the Pi. In the event that the Pi goes down, the Pico closes the relay, the Pi gets powered off. When the relay reopens, the Pi turns back on.
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My Loony Tunes idea: The same as the above, but the Pico powers a tiny solenoid that hits the Power On button.
I love this. I could put googly eyes on it.
I think the idea of the relay is strong so I’ll start there.
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Glad to have helped, Pix, I hope the project goes well 
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As a non frequent pi users, by default wont it always be on if there is power? i.e. there is no power button, by default.
Hey @Michael99645 ,
The Pi 5 is a little different from previous versions in that it now has a power button on the board. If it experiences a complete loss of power, it will automatically reboot once power is available again, but a brownout or partial loss of power will cause it to safely shutdown and only reboot properly once it is power cycled.
Jane’s idea involved finding a way to manually reboot the Pi by pressing this button.
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Something I don’t know is when I should use a MOSFET and when I should use a relay.
Can you give me some guidance here? Why did you nominate a relay for this application?
Honestly, Pix, I just said relay because I had been looking at them earlier that morning so they were still front of my mind.
When you’re dealing with large voltages, i.e. Mains, or when you need the logic circuitry to be isolated, relays are going to be the better choice. If you need speed and relative silence, MOSFETs are gonna be the go.
For this kind of project, neither one is really “better” than the other. Since the Up Time on this project is going to be limited by the Pi’s Boot Cycle anyway, the choice of a Relay vs a MOSFET is really down to personal preference. The mechanical click of a relay might even alert you to the downtime, for instance.
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Thanks for that, makes perfect sense, I missed the button when looking at the pinouts 
Hello all, I have been across the ditch for 3 weeks and now back home for a well-earned slow down.
Anyway, in this post are we talking about the pi booting up the OS on power-up or auto starting the required app on power up.
All computers on power up are set to boot and after all necessary procedures included in the boot make the device ready to the user as deck top or as command line interface.
As for auto starting the app after boot then I have found with the PI Zero and the app including Tkinter that I still have not solved this problem. I offered a post on this fact some time back, without any luck.
Maybe if you don’t want your PI to shut down on power failure you should include some battery backup to prevent the shutdown.
Regards
Bryan
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I agree with Byran, for mission critical, zero downtime devices - battery backup or a a UPS would be best - some Pi 5 UPS HATS can do all sorts of management functions.
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