chipace
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raspberry pi 4 power button (GLOBAL_EN and RUN)

Sun Jul 07, 2019 5:35 am

I have found a great new way to add a power button and it has been working flawlessly, but I am not sure how electrically safe it is.
I take a tactile button and connect it between the GLOBAL_EN hole and RUN hole. I press it when I want to boot my RPi4. GLOBAL_EN appears to have a pull-up to 5V and RUN is at 0V when shutdown.

Here is the specific button that I am using (I bought it from Sparkfun):
https://www.sparkfun.com/products/10302

There are 4 pins, I snap 2 off (both from the same side) and just push the remained 2 pins thru the GLOBAL_EN and RUN board holes (solder not necessary). The pitch of these pins is 5mm (they fit in a breadboard with one space between them). It fits perfectly flush on the board.

Any thoughts on long term damage to the SOC?

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DougieLawson
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Re: raspberry pi 4 power button (GLOBAL_EN and RUN)

Sun Jul 07, 2019 5:49 am

chipace wrote:
Sun Jul 07, 2019 5:35 am
There are 4 pins, I snap 2 off (both from the same side) and just push the remained 2 pins thru the GLOBAL_EN and RUN board holes (solder not necessary).
WRONG!

You don't want to have anything loose on your Raspberry circuit board, if it comes out that could cause a critical short circuit. Solder it in, it's not hard to learn soldering.

https://projects.raspberrypi.org/en/pro ... -soldering
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Gavinmc42
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Re: raspberry pi 4 power button (GLOBAL_EN and RUN)

Sun Jul 07, 2019 8:47 am

Solder some header pins on and use the power switch and wiring/connectors from a old PC case?
Any official documentation yet on these pins?
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Milliways
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Re: raspberry pi 4 power button (GLOBAL_EN and RUN)

Sun Jul 07, 2019 12:31 pm

The schematic says **NOTE RUN IS 3V3, GLOBAL_EN IS 5V** so seems inadvisable (apart from the general risk of connecting anything you don't understand)

hippy
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Re: raspberry pi 4 power button (GLOBAL_EN and RUN)

Sun Jul 07, 2019 1:56 pm

chipace wrote:
Sun Jul 07, 2019 5:35 am
I take a tactile button and connect it between the GLOBAL_EN hole and RUN hole. I press it when I want to boot my RPi4.
Interesting idea and pulling GLOBAL_EN to 0V seems to now be the recommended way - the only way currently - of bringing a Pi 4B out of a shutdown / halt state.

I would be cautious of 5V being put on what is a non-5V tolerant RUN signal line, even though that goes through 100K. But given the PMIC seems to hold Power Good (PG2) to 0V (ish) when shutdown there should be no over-voltage going into RUN on the SoC. PG2 would not it seems be anything other than 0V (ish) until the switch was open-circuit and GLOBAL_EN allowed to be pulled-high.

The big unknown is what happens when the '5V' GLOBAL_EN is shorted to the 3V3 RUN signal when it is not shutdown. Of course that will only happen when the button is pushed.

The problem is we don't have publicly available full circuit diagrams or datasheets so it's hard to properly asses how safe or not doing that would be.

I would probably risk it myself but the recommendation tends towards "don't" and, if you do it, you have to accept all consequences of the risk involved.

An RPT hardware engineer would be able to give a more definitive answer.

But definitely solder on 0.1" headers and plug your push button into that if you are going to do it. I would probably recommend a slide switch rather than a push button switch, or maybe both for extra security to avoid accidentally pushing it.

chipace
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Re: raspberry pi 4 power button (GLOBAL_EN and RUN)

Sun Jul 07, 2019 5:33 pm

Thanks Hippy! As you said, the 5V to RUN path would go thru 100k and then an additional 100 Ohms to the SOC pin... if there were clamp diodes inside the SOC on the RUN pin (not a crazy expectation for a power related input) then that would be 100% safe. I wish that someone with direct knowledge could confirm that, as this is a very easy way to add an on-board power button for $0.25

I tried bending one pin to see if I could make it the 2.54mm pitch that would allow it to safely connect to GND, and that appears to work.
I will solder that up today.

chipace
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Re: raspberry pi 4 power button (GLOBAL_EN and RUN)

Sun Jul 07, 2019 8:14 pm

After soldering the push button between GLOBAL_EN and GND, I am noticing that the button now acts like a WAKE/RESET. When the button was between GLOBAL_EN and RUN is only acted as a WAKE.
I would prefer just the WAKE, but without more details about the BCM2711B0 RUN pin the GND is probably safer.

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