How can I reroute multiple signals from a 4 pin connector using a relay switch?

[Tom.G]

@Next_Of_Kintetic, for the reasons you just discussed, I recommend you stick with your original latching relay approach.

 

[pbuk]

Although, couldn't I use those as well to send signals to the relay board that you linked?

What the 3.3V pins? No, these are always at 3.3V. They provide power (up to 500 mA if I remember correctly) for attached circuitry e.g. this neat little real time clock module. You could use them to provide power to the relay board, but 3.3V relays are hard to find, you would be better off using the 5V pins: see below.

That's kind of the point I was making though. Because then what happens if I switched to the "NO" position last time before I turned off the 3d printer. If I also turned off power to the relay (or let's say a surge happens, power gets cut off), then the relay reverts back to its NC state. When power comes back on, wouldn't it remain in the NC state unless something tells it to switch again?

Yes: don't turn it off (I would power the relay from the 5V pins (2 and 4) on the GPIO connector so this was not an issue - you don't need a separate wall wart at all). I think recovery from a power outage is going to be more complicated than just having the Pi remember which feeder is feeding.

Actually forget about building it yourself, just use one of these: leave the jumpers off and bridge P25, CH1 and CH2 together (so that 2 of the SPST relays are switched simultaneously by GPIO 25).

Wait, and this is probably my overall confusion about the subject, but I thought the point of opto-isolation is to protect high voltage surges from other parts of the system from wrecking circuitry that is not resistant to that high voltage.

No, the principal point of opto-isolation is to prevent you from being electrocuted. It (or some other physical separation) is a requirement in the UK (and I believe in the US) when switching line voltages from a device with low voltage connections (the wires to the Pi from the relay box if this is in a separate enclosure) or exposed metal (the USB connector on the Pi if this is in the same enclosure).

I mean, do I not have to worry about a high surge occurring within the relay from say the wall wart and then "cascading" back to the Pi?

No, the wall wart already includes protection from line voltages appearing on the output, the same goes for the printer and its control lines to the feeders. You only need to worry if you are switching line level voltages.

 

[Next_Of_Kintetic]

Hi everyone,

Sorry for the late response, but I have been extremely busy this last week (what else is new).
And I will unfortunately have to put this project on hold due to various life related circumstances.

So, I just wanted to thank you all for all your help and responses.
As for what I end up doing eventually (if I decide to use a latching relay or a powered relay -- that is something I'm still not sure about at the moment). I might even seek out other possibilities in the future. Either way, just wanted to thank everyone again for all their help. I have learned a lot from these discussions.

If I end up coming back to this project, I will just open a different thread if need be.
Feel free to lock or archive this thread.
Thank you all again. Until next time.