Fitting a power button

[Malcolm Ray]

If you use a Raspberry Pi 5, you probably know that it has a tiny power
button (next to the power LED). This is quite fiddly to reach from the
front of the PiDP-10. What's less well known is that there's a jumper
which allows you to fit your own external power button. I've just done
this, using the existing cutout intended for a key switch, and I think
it's an improvement.

Here's some documentation about the power button and jumper, with a
photo:

https://github.com/raspberrypi/documentation/blob/develop/documentation/asciidoc/computers/raspberry-pi/power-button.adoc

What you need:

1. A normally open momentary on-off push button to fit a round 12mm
panel hole. I bought a pack of these:

https://www.amazon.co.uk/dp/B0825RCZJS

Sadly, the pre-soldered wires on these are not long enough, so you'll
need to remove them and replace them with longer ones. Note the plastic
rear body of these buttons, to minimise the chance of shorting
anything, because the button comes close to the bottom of the LED
panel.

2. A 2-pin header to solder to the Pi jumper. Just cut it from a longer
header strip (see below).

3. Two leads with a female Dupont connector at one end, bare at the
other end. I have a suitable crimp tool and parts, but of course I was
unable to find my female Dupont receptacles, so I gave up and
sacrificed an existing male-to-female patch lead, cutting off the male
end. 22cm is about the right length: you need some slack, for easy
fitting.

4. Heat-shrink sleeving, to make a neat job when you solder the leads
to the button.

5. Four longer nylon standoffs, M2.5 x 25+6 mm, to replace the existing
20+6mm ones. You might be able to get away without these, but it's
tight: the top of the Dupont receptacle butts up against the rear of
the light panel, which isn't good. So I chose to create an additional
5mm of space. For example:

https://www.amazon.co.uk/dp/B0BWXLLJS8

6. A "booster" header for the Pi, to compensate for that additional
5mm. For example, this kit has a selection, including a single row
which you can use for the aforementioned two-pin header:

https://www.amazon.co.uk/dp/B0828SRBTC

Remove the Pi from the case. Remove the rear panel and the LED panel,
to give access to the screws for the standoffs. Replace the four
standoffs with the longer ones, and screw the LED panel back into
place. Solder the two-pin header to the Pi's J2 jumper (though I
couldn't see it labelled as such on mine: see the above photo for where
to find it). Install the booster header on the Pi. Cut the existing
short leads off the button, clean up the solder tags, solder the new
leads into place, and finish with the heat-shrink (you did remember to
thread the sleeving onto the leads before soldering, right?). Thread
the leads through the back panel's switch hole, and fix the button into
place with the nut and washer. Put the back panel into the case,
routing the leads to where they'll be needed. Refit the Pi, pushing the
Dupont connectors onto the new jumper (this is a little fiddly). Screw
the back panel into place.

When you plug in the power, the Pi will come up as normal (no need for
the power button yet). When you want to shut down, ensure a clean
shutdown of the PDP-10 OS first, as usual, then push the button twice
in quick succession. The first results in a dialogue box on the
desktop, asking whether you want to shut down, reboot, or logout. The
second press confirms that you want to shut down, so the Pi will shut
down and power off. To bring it up again, just press the button once.
If Linux ever hangs, press and hold the button for five seconds, to
force an unclean shutdown.

I find this easier to use than the Pi's onboard power switch: I can
always find the new power button "blind". Obviously it precludes using
a kwy switch, but the installation is easily reversed later, if I
change my mind.