Immediate power up with external power, safe shutdown when removed

[shawnj007]

TL;DR - How to make the unit boot immediately when external power is applied and safely shutdown when external power is removed?

Use case:

Stationary, mounted Rpi (no direct access to circuit board and buttons), with touchscreen.

I need the Rpi to boot ** as soon as ** external power is applied.
I need the Rpi to safely shutdown ** as soon as ** external power is removed.

How do I get the UPS HAT to behave in this way using the PMS Python API? The unit will not have regular wifi access so the Power Software is not a good solution either.

I can accomplish the shutdown by querying the mode every few seconds and creating a shutdown event. Regardless of which way it is shutdown, the Rpi does not boot again when external power is re-applied.

The only way I have gotten it to boot again is by using the ‘battery level solution’, but this is a poor solution because it requires a 5% point rise in the battery level before the Rpi powers up. This can take 5-10 minutes depending on charge state. Worse yet, a safe shutdown setting between 95-100% causes the unit to continuously boot/shutdown.

S

[shawnj007]

So, no real fix from sixfab, so I came up with something that does the trick.

My solution is to simulate a button press when power comes on with hardware using a 555 timer IC. This works for me, it may work for you, but use it at your own risk.

The circuit operates by sensing voltage on the power source and uses a mosfet to simulate a quick press on the button. Since the ‘short press’ has no effect when the system is already on, power can be applied/removed in cases where the normal safe shutdown (battery level) is being used. I do not use it in this way.

I added some code to read_sensors.py that responds to the battery state and initiates a shutdown. To boot from a hard shutdown, use S1, from soft shutdown, use S2.

To run the read_sensor.py script at boot up, add:

@/home/pi/startup.sh

to the end of:

/etc/xdg/lxsession/LXDE-pi/autostart

and place the startup.sh file in the appropriate place. It will run:

x-terminal-emulator -e ‘cd /home/pi/Gits/sixfab-power-python-api/ && watch python3 ./example/read_sensors.py’

to launch a window at startup to monitor the operating mode It monitors system input power, since during high power usage, it will be in BATTERY_POWERED even when plugged in.

(This would be more correctly described as ‘BATTERY_DISCHARGING’)

The schematic, cnc, and all the needed files can be obtained from my git:

shawnj007/QuickReset

[shawnj007]

Here is a better solution that doesn’t require any external hardware:

[SOLVED] How to make Easy Deployment Mode enable just before shutdown!