I’ve been looking for a solution to my problem now for a few weeks and can’t rly find a good solution

So all help is very much appreciated.

Basically I want a relay to work as a momentary switch

My projector has a 12v trigger signal and I want to use it to power my raspberry pi on and off but you can’t just cut the power.
I need to bridge 2 pins to safetly turn the pi off with a script that runs when the connect

There is a lot off diy and tutorials with a momentary switch but since I want to use my projectors 12v trigger signal I’m kind stuck

 

Or is it maybe some kind of logic gate circut I need?

 

There are a few things missing.

1. 12 V trigger signal
Is it momentary, constant and what available current?

2. How long does the momentary signal have to last? (e.g. 1 s)

Some hints.

There are delay on make timers. This can give you the momentary signal.

You may need to convert the 12 V signal to a contact closure with a relay. This can actually be done with a small solid state relay or OPTOMOS part which is FET controlled by an LED. This usually works well. You have to worry about on resistance, so you have to know if say 100 ohms is the same as zero ohm contact closure.

You can build your own. See TIMERBLOX. http://www.analog.com/media/en/tech...Journal-V20N4-01-df-Timerblox-Andy_Crofts.pdf

 

The 12v trigger signal is for motorized movie screen so when projector is turned on the screen goes down and when it’s turned off screen goes up. And 12V trigger only outputs a DC 12V signal

Think time doesn’t matter as long as it’s not on/off like a latching switch

Sry if my explanations is bad I’m a newbie to this I know how I want it in my head but hard to explain in words

I going to try to explain better

When I turn on my projector it sends out a 12v trigger signal that I want to act as a momentary switch to my raspberry.
I could use a relay to just cut power on and Off with that but it can cause ssd corruption.
So I need to use a script on the pi that use the GPIO pin 3 And connects the two pins (shorting them since one is ground) giving the pi knowledge to turn on. And when I turn the projector off the 12v trigger signal is cut off and then again I want the pi to get same signal as before and run the script and safely shutdown. So something that give signal on power on and power
like relay goes on and off fast but that’s not possible since when projector is on it keeps sending the current/signal to the relay and when I turn off projector the relay turns off and will not give a signal I think



Hope I don’t make it more messy to understand.

 

Ignore the relay nonsense for now and work on your scripts. We can do that with a relay or a small opto-FET and a resistor.

That said and done. I don;t know the details of the PI ports, BUT the ports may have pull-up or pull-down resistors that can be enabled.

In your case, it;s likely a pull-up, because you want a contact closeure to ground. A rely can be used to invert the ON/OFF state. With the opto-FET it's harder. PI-Power up is a contact closure to ground. HI to LOW transiion on the port. PI-Sleep is ground to logic HI or LOGIC low to logic HIGH transition of the port.

Your script should look for an edge. e.g. a low to high transition or a high to low transition.
You could poll every second to determine what edge occurred and in your case "start-up" or "sleep" which is what I think you want to do.

Your edge detection can be done by polling. i.e detect a change in state every 1 second.