I found READING to be probably the very best thing I got from school in the first few years. Suddenly the whole world of books was open to ME!! Everything from an old stack of TOM SWIFT books to all sorts of technical material was mine to learn. Suddenly the mysteries of electrical power were explained. Both OHM's Law and the current to power! All there just for opening a book.

As for the comment about size, really it has as much to do with the mechanical durability and logistics of an assembly. Not only does a circuit need to function correctly, it also needs to survive the rough treatment of the real world, where there is vibration and bumps and things get stepped on. The transceiver that works on the bench or desktop may not last very long when it is mounted in a car, unless it is packaged adequately. So the mechanical aspect of an assembly is a serious matter, if it needs to survive. THAT is why my career includes the design of the physical arrangement of all of those electrical and electronic parts. And where visualization saves a whole lot of sketching paper.

 

I didn't see any mention of need to have the system shut down at some given point.

Seems the sentence below says the short remains (I assume contacts closed) until both inputs go to zero.

I need the wires to be shorted only when both the inputs go live, once it's shorter I need it to remain shorted until both inputs drop to 0v.

 

I think that's where I'm getting confused. "Both inputs go live". "Once it's shorter" ? ? ? "I need it to remain shorted (assuming closed) until both inputs drop to 0V."

IF I can salvage anything out of this it's that the OUTPUT goes high when both inputs go high. The output remains high until BOTH, not just one, BOTH (assuming inputs) go low ("drop to 0V"). So it takes two HIGH inputs to drive an output High. Output remains high until BOTH inputs drop to zero volts. In theory A & B go high and the output goes and remains high. A OR B can go low but output remains high until ALL inputs are low.

I guess the reset button on my drawings is out.

If we assume that a LOW INPUT is equal to ground (common ground) then I can imagine a 2 input gate arrangement along with some steering diodes. Once both inputs go high an AND gate goes high. One of those high outputs can feed back to one input and the other input is through a diode. Once that input goes low that will force the AND output low even though it's feeding back on itself. If, however, the input is either High or Floating (not grounded) then this approach isn't going to work. Not without being able to drive a hard ground to the inputs.

I'd have to spend a few bits of time thinking about a solution to meet this requirement. IF I UNDERSTAND THE GOAL.

 

Typically after making this post I went back to the circuit simulator and finally managed to get my head round it and came up with a solution using a few small relays.

Thanks.

I think the TS is done with this thread. We're not going to get any further input from the TS. This is now an argument between us as to how to achieve this goal. But if he's solved his problem then I'm done trying to help.
Unwatched.

 

I think the TS is done with this thread.

Probably as he mentioned finding a solution in post #7 "using a few small relays". Further post to show how it can be done using different configurations and fewer components may have been viewed since the TS was last seen on Friday at 12:02 PM and are also for our enjoyment and anybody else viewing who might have a need for such a circuit.

 

It was an interesting challenge, a scheme enabling with an "AND" function and then holding with an "OR" function.
That, coupled with terminology confusion made it a bit of a puzzle. I never use "shorted" in describing a circuit function. And it is not likely that the inputs are both active pull up and active pull down.