# Black Box project, Help!

## How can I do it?

• ### Multiplexer?

• Total voters
0

#### Maireny

Joined Nov 22, 2015
4
Recently, my professor gave us a project to do in one week, but the thing is, I'm clueless of where I should begin with. I'm not asking you guys to do the project for me, but to give me some ideas of where I can begin, or what components should I use. And I'm not the only one going crazy because of this project, almost the whole class is, because the professor is TERRIBLE! He doesn't know how to explain. So, if any of you have idea of how to start doing this, please share it with me!!

#### AnalogKid

Joined Aug 1, 2013
10,062

#### WBahn

Joined Mar 31, 2012
26,398
The first step is to create a truth table showing what each of the outputs should be for each of the possible input signal combinations.

#### KeepItSimpleStupid

Joined Mar 4, 2014
5,088
The second is to do the Karnaugh map thingy.

Remember than anything can be built with NAND or NOR gates. It's like DNA.

#### WBahn

Joined Mar 31, 2012
26,398
Part 1(d) is one of my pet peeves. They tell a student to prove that something is minimized and, in most cases, never explain the metric by which one solution is to be judged more "minimized" than another.

I came to the general conclusion a long time ago that this is mainly due to the incestuous nature of higher education and the fact that so few people that write textbooks have any significant real world experience (to say nothing of the people that teach).

#### WBahn

Joined Mar 31, 2012
26,398
MOD NOTE: Moved from Project Forum to Homework Help.

#### Maireny

Joined Nov 22, 2015
4
MOD NOTE: Moved from Project Forum to Homework Help.
How do I do that?

#### Maireny

Joined Nov 22, 2015
4
I think we want us to use only basic gates to build this. I'll try to start by making a truth table and then trying to come up with a ecuation base on the table. Am I in the right path?

#### Maireny

Joined Nov 22, 2015
4
The first step is to create a truth table showing what each of the outputs should be for each of the possible input signal combinations.
I already have a pretty clear idea of how to do it thanks to your comment. But I'm still confuse about the output saying if theres an error on the inputs. I've been thinking that I could do it with XNORs to compare the inputs and see if the are equal so in that way I would know if there is more than one high level on the inputs. Am I in the right path?

PD: sorry about my english, I'm a foreign student

#### WBahn

Joined Mar 31, 2012
26,398
How do I do that?
You don't. I did. The note is so that you know that it didn't just magically jump forums and so that any readers that saw it over in the original forum don't mistake it for being a duplicate thread.

#### WBahn

Joined Mar 31, 2012
26,398
I already have a pretty clear idea of how to do it thanks to your comment. But I'm still confuse about the output saying if theres an error on the inputs. I've been thinking that I could do it with XNORs to compare the inputs and see if the are equal so in that way I would know if there is more than one high level on the inputs. Am I in the right path?

PD: sorry about my english, I'm a foreign student
You have four inputs. How are you going to compare the inputs to see if they are equal and, even if you do, how does that tell you that more than one is high?

Could you make a signal that is HI if A and B are both HI?

Could you make a signal that is HI if C and D are both HI?

Could you make a signal that is HI if either of the prior two signals is HI?

Does that give you an idea of how you might proceed? (Hint -- the above isn't complete, just a start)

#### AnalogKid

Joined Aug 1, 2013
10,062
I already have a pretty clear idea of how to do it thanks to your comment. But I'm still confuse about the output saying if theres an error on the inputs. I've been thinking that I could do it with XNORs to compare the inputs and see if the are equal so in that way I would know if there is more than one high level on the inputs. Am I in the right path?
Think of the error detector as an extra layer of logic wrapped around the operational part. Once you have a circuit that gives the correct outputs, you can add a layer that detects if any of the valid outputs are asserted. So if the valid outputs are A, B, or C, a NOR of A, B, and C will detect if none of them are true - the error state.

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