Logic Puzzle time or How I learned to love Logic and solve everything with it?

[mkiijam]

I need to stop relay A from changing state when relay B is on. Can it be done with logic gates and their slightly expanded universe? Just no MCU's or the like. Latching relays would be okay and I think I need momentary switches.

But for the exercise I was trying to stay just with logic chips for the... ehhh.... logic, as opposed to mechanical interlocks etc. Driving the relays could of course be transistors or something, but that's not a concern at this point.

Can it be done? I've ben pulling my hair out for hours! What am I missing?

[IanB]

Break the problem down into logical pieces.

First of all, relay A needs to be driven by a latching circuit (a set-reset latch), which will then receive a signal to turn it on, and a signal to turn it off (or a single signal to make it change state--your choice). You need this so that relay A can stay on or off by itself, without needing any continuous external signal.

Secondly, when relay B is on, it needs to interrupt the signals going to the latch for relay A, so it cannot receive any commands.

[mkiijam]

Secondly, when relay B is on, it needs to interrupt the signals going to the latch for relay A, so it cannot receive any commands.

Yes, this is so very true. But this is a mechanical interlock solution, no?

[Andy Chee]

Yes, this is so very true. But this is a mechanical interlock solution, no?

You’re already using mechanical relays for relay A & B, so I’m not sure why a mechanical solution is being ruled out.

Perhaps relay A & B are exisiting in a piece of equipment already and cannot be altered?

[mkiijam]

An SR latch with a latching relay is getting me in the right direction... not there yet but much closer!

[IanB]

Yes, this is so very true. But this is a mechanical interlock solution, no?

It doesn't have to be. Logic gates can also implement a switching function. For example, an AND gate.