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My Pi Zero is powered by a small ATX PC power supply that is also powering a few other components: projector, audio amplifier. I'm using the gpio-shutdown device tree overlay to add a power button on the BCM pin 3 interrupt.

This works great, except that the Pi initiates the boot sequence when the PC power supply is turned on. This is not what I want; I want the boot sequence to start only after power is applied AND the power button attached to BCM 3 is pressed.

Is there a way to accomplish this - to start the Pi when the power button attached to BCM 3 is pressed?

Seamus
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RyanScottLewis
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1 Answers1

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IBM computers have circuitry to hold the processor in HALT state until voltage is stable.

You could do similar on the Pi by pulling the RUN header low. This will require additional circuitry, but as we don't know what you are using this is up to you.

PS ATX power supplies are a poor choice for the Pi. They are designed to supply large currents, and perform poorly if lightly loaded!

Milliways
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  • May want to include what the Run Header is... and where it might be found on the Pi Zero W {I'm still looking around for a decent source of info on this one} – RubberStamp Sep 16 '18 at 00:22
  • @RubberStamp there are 4 pads near pin 39 (you need to add your own header on all Pi models) and one pin is clearly labeled RUN - _ must admit I haven't used Pi Zero W RUN, but all my Pi models have it - most have reset button soldered on – Milliways Sep 16 '18 at 02:02
  • Now I see it on my Pi Zero ... My soldered on GPIO header was partially obscuring the silkscreen... – RubberStamp Sep 16 '18 at 11:49
  • This doesn't have the effect I'm looking for. Pushing my power button (bringing BCM 3 low) doesn't turn on the device while the RUN header is pulled low. – RyanScottLewis Sep 16 '18 at 21:57
  • @RyanScottLewis The ONLY way to stop the Pi (with standard firmware) from booting when power is applied is to hold the RESET pin low. You need to release this to boot. (Frankly I don't understand why so many Pi users want to control power - unless using batteries there seems little point.) – Milliways Sep 17 '18 at 00:42
  • @Milliways I'm building a sort of PC with many things being started once the Pi is booted with Systemd units. So, preventing the Pi from booting until my power button is pressed prevents everything from being turned on once the power supply has power.

    I think I'll set this question as answered and use some sort of combination of RUN header & the BCM 3 power button to get the result I'm looking for.

     – RyanScottLewis Sep 17 '18 at 00:57