# Does this circuit work in reality?

i have a project (designed in CircuitMaker2000), i wanted to see if it works in real... (track the OUTPUT routes to the 3-inptut gate)

Jack A Lopez1 year ago
Hey, um, I just noticed that you've got outputs of gates wired to each other.  I mean specifically the outputs of those 3-input ANDs, the ones you've got wired together in groups of four.

You can't (or rather you shouldn't) do that.

I mean what happens if the output from one gate is a 0, and another is a 1, and both those outputs are connected together to the same wire?  The answer is these outputs short each other, and the actual voltage on that wire is ambiguous.  That's supposing the outputs do not source+sink enough current to melt the gate.

I guess I did not actually look at the circuit closely on my first attempt at answering this question.

Although my advice to try Logisim might be good advice, supposing Logisim would tell you can't directly connect the outputs of gates to each other (i.e. tell you such wiring is an error condition).  In contrast, a more realistic simulator like CircuitMaker might actually let you do something dumb like that.

BTW, the only practical case in which the outputs of two (or more) logic gates can be wired together in parallel like that, is the case in which the outputs are guaranteed by the logic to be identical.  That way these gates all source, or all sink, current at the same time, without shorting each other.  And the only reason why you'd do that is just to increase the total current that could be sourced or sinked, basically combing several small wimpy gates into one big beefy one.

~CableGuy (author)  Jack A Lopez1 year ago
then how can i fix it?
1 year ago
The answer depends on what you are trying to do with those four signals.

I am guessing you want to "combine" those signals somehow.

Maybe you want to OR four signals together?  If so, then feed them into a 4-input OR gate.

Maybe you want to AND four signals together?  If so, then feed them into a 4-input AND gate.

I mean that's sort of the game here, right?  How do you combine digital signals together? You do it using logic gates.
Jack A Lopez1 year ago
I remember asking myself a similar question not too long ago, about a circuit that was purely a collection of logic gates. The question being, what would the circuit actually do if it were wired together correctly?

Then I found a free logic simulator called Logisim,
http://en.wikipedia.org/wiki/Logisim
http://ozark.hendrix.edu/~burch/logisim/index.html

I pretty much just used Logisim that one time, but I found it worked really well, and for the circuit I was building it gave the same results as a the physical  electronic circuit wired on the lab bench out of logic ICs.

So I suggest simulating your circuit in LogiSim, and seeing what results that gives you.
mrmerino1 year ago
What's going on with those two gates on the left? I think they're AND gates, so all they do is turn on when you press the button... why not just press the button to turn on the power?
verence1 year ago
No idea if it works, and far to lazy to figure that out (- what should it do anyway?) Just, unless the 3input AND gates aren't open collector output, you can't just connect the outputs. If they are OC, the pull up resistors are missing.