Powering off via UI while using a Mausberry Circuit

cyperghost

@caver01 We will change this via SSR-GPIO software switch ;)

caver01

What I need is a normally open switch that closes when power gets cut. If I wired that in parallel with the power button, it will trigger when the Pi shuts down without any need for a GPIO command to be sent.

<EDIT> ha ha I just read the first sentence on the link to the SSR. Says it is a normally open switch. . . I may have to pick one up.

cyperghost

@caver01 Normally means powered, so indeed it should work ;)

caver01

@cyperghost
Ok, so I was thinking if we had a component that was OPEN when powered, but closes when the power goes off, we could wire this to a power pin and in parallel with the power button. It would trigger the mausberry like a button press when the Pi goes off. But that would make the circuit think the power button is being held down!

So, if you plug in the system, it would power up immediately. Maybe it would even loop.

cyperghost

@caver01 But the mausberry works with permanent switches?
But I think the real button won't work anymore ;(

So use a GPIO to set event on/off ;)

cyperghost

@caver01
So you soldering the SSR next to your switch. So you have two switches running.
I'm guessing the hardware switch is a momentary one - with normal state off?
So the SSR can also act as a momentary, unpowered via GPIO it is off, powerd via GPIO it is on....

So it think it should work ;)

caver01

@cyperghost said in Powering off via UI while using a Mausberry Circuit:

@caver01 But the mausberry works with permanent switches?
But I think the real button won't work anymore ;(

So use a GPIO to set event on/off ;)

Yep. use it to trigger an actual (parallel) button press.

What I can't figure out is why, even after the pi shuts down with a soft shutdown, the mausberry ignores my button presses. It is like it locks into a powered state. It must be checking the state of Pin 2:

If Pin2 = 0 and power button is closed, DO POWER ON
if Pin 2 = 1 and power button is closed, DO POWER OFF

so, after a soft shutdown, the mausberry thinks I am trying to turn the pi back on, but it is already on, so it does nothing. It's like an anti-bounce state, the time right after a POWER ON, but before the script is running and can set Pin 2 = 1.

caver01

@cyperghost If I get one of these to test, I will need help. Which pin on the SSR goes to what, and which pin gets the resistor?

cyperghost

@caver01 page 7 shows connection diagramm
Pin 1 goes to positive value (= GPIO Pin), Pin 2 is ground, set a resistor with right value (330ohm for 3.3V).

Pin 3 and 4 is the switch ... Connection does not matter here see page 4, it is independent if you switch the ground or positive value.

caver01

@cyperghost Looks like the diagram has the resistor on Pin 1. Does it matter?

cyperghost

@caver01 No but the resistor has to be placed somewhere in the line (+) LED (-)
So (+) R LED (-) or (+) LED R (-) doesn't matter

caver01

@cyperghost Oh I get it. . . because the device itself uses an LED internally for actuation.

Hey, thanks for your input here and the fun conversation about this. @madmodder123 I hope I didn't overstep by totally dominating your original post. I think we were on the same page with this, and it looks like a little testing may prove that while the Mausberry circuit is an excellent solution for an add-on power switch (especially when coupled with the updated script), it comes with an assumption that the button you add will be the only shutdown method used. It is not setup with awareness of additional soft shutdown procedures that aren't triggered by the button and the circuit itself.

cyperghost

@caver01 I'm pretty sure that a normally opened ssr works together with a momentary switch!

Annother suggestion. I think if we use a normally closed SSR and connect it to the $GPIOPin2 so there is no current as long as the Pie is active. But if is inactive it would close the reset pads of the mausberry... do you think that may work?

cyperghost

Some "improvments" to the original script! It might be a bit faster as there is no if-then-else....

#!/bin/bash
#this is the GPIO pin connected to the lead on switch labeled OUT
GPIOpin1=23

#this is the GPIO pin connected to the lead on switch labeled IN
GPIOpin2=24

echo "$GPIOpin1" > /sys/class/gpio/export
echo "in" > /sys/class/gpio/gpio$GPIOpin1/direction
echo "$GPIOpin2" > /sys/class/gpio/export
echo "out" > /sys/class/gpio/gpio$GPIOpin2/direction
echo "1" > /sys/class/gpio/gpio$GPIOpin2/value
power=$(cat /sys/class/gpio/gpio$GPIOpin1/value)

until [ $power = 1 ]; do
    power=$(cat /sys/class/gpio/gpio$GPIOpin1/value)
    sleep 1
done

[ $power = 1 ]  && echo "Shutdown now!" && poweroff

caver01

@cyperghost
Nice.

I used to use a python script that did edge detection. I was led to believe that keeping a python script active in the background would be even less of a CPU burden than a polling bash script. But I changed to the bash script you helped build when I saw the better commands. It would be nice to convert it to python.

cyperghost

@caver01 can you post python code please?
I think python is the better choice - if you enable IRQ mode, then it's the fastest alternative ;)
But the old bash script looked a bit weird so I made it a bit cleaner looking

caver01

@cyperghost I will post it later when I am back to my Pi.

cyperghost

@caver01 I will be online in a few hours again. At work I asked a colleague (circuit designer) how this issue can be solved. It's possible to switch the event just via a transistor - but I forget which type ... I think N-type, but you need some resistors (at lease one at base) and best a diode (for current switchbacks) the make sure switch behaviour.

On the other hand he said, that the optical-mosfet is also a nice method to trigger that and it's really fail safe as the circuits are isolated.

Then I asked the method with the reset trigger... Clear answer: NO! A reset is a reset as you don't know what there really happens. It can be named as "emergency exit" if the µc is trapped but never should be used as regular switch.

caver01

@cyperghost I am glad you confirmed the transistor idea. I was actually going to try that first based on other things I have read. I believe I need to use an NPN transistor, and I have a bunch of them collected from old hardware. Here is an example where someone is using a transistor to trigger a button press for a camera trigger. The SSR is suggested first, but someone concludes that a transistor method would be adequate.

Most discussions elsewhere online regarding this topic mention the use of the opto-coupler SSR as a safer method, as it isolates both sides and you don't have to worry about linking the grounds. However, I am not that worried about isolation, and I won't have to buy anything to try it.

I didn't get a chance to lookup my python script last night. I will post something soon, and I will definitely try the transistor trick.

cyperghost

@caver01 Thank you for the linked document with the transistor. As you use the same potential there should be no drawbacks with connecting the Pie and the mausberry.

As said, the SSR is the easiest method at all.