I think I understand the Raspbery Pi GPIO pins and most of how this diagram below works, at a high level at least.
First question, it's not clear to me exactly how the middle part with the resistors and transistors works. Can anyone help explain how this works in another way? This is essentially flipping the high/low logic from the GPIO pins so a low output from the pi is non-zero voltage to the relay input?
To power the LED's on the other end of the relay, I have a wall AC adapter to 28VDC, .9A that will power a 700 mA driver. The driver will connect each of the relay terminals to the LEDs. I will only need one led/relay active at a time.
My second question, if I run 8 wires from the relay terminals to power each LED, can I connect them all to the same wire for ground to return? I'd like to have some sort of quick disconnect for the LEDs so they can be easily unplugged, can you have multiple quick connect terminals spliced into a shared ground or is that a bad idea? Any recommendations for quick disconnecting plugs?
Still pretty new to all of this so I feel like I could very easily miss anything from "common sense" and "good practice" to "just completely wrong".
Here's the LEDs I was planning to use in a series to justify the 700mA current.