# Digital truth table to digital circuit

#### gandoN9

Joined Oct 12, 2020
18
Hello,

Truth table:

Making digital circuit from that truth table:

I have question about the circuit (if A,B,C are 1, then Q is 1), can i make this circuit like that, if not then why?

Help will be appriciated, thanks!

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#### ronsimpson

Joined Oct 7, 2019
1,227
i make this circuit like that
You did is right. (/A and /B and /C) or (A and B and /C) or (A and B and C) ["/" in not]
Are you to make it "simple"? If so look at he last two lines. 110 & 111 this is the same as 11x where x is 1 or 0. For gastes AND2 & AND3 find one solution for A=1 & B=1.

#### gandoN9

Joined Oct 12, 2020
18
You did is right. (/A and /B and /C) or (A and B and /C) or (A and B and C) ["/" in not]
Are you to make it "simple"? If so look at he last two lines. 110 & 111 this is the same as 11x where x is 1 or 0. For gastes AND2 & AND3 find one solution for A=1 & B=1.
So both circuits what i made are right?

#### MrChips

Joined Oct 2, 2009
23,507
Another way (and perhaps a better way) to do logic simplification is with the use of a Karnaugh map.

#### WBahn

Joined Mar 31, 2012
26,398
So both circuits what i made are right?
I don't see a difference between them? Maybe I'm just missing it.

There are MUCH better ways to draw your circuit diagrams than what you did. They are very hard to follow.

#### gandoN9

Joined Oct 12, 2020
18
I don't see a difference between them? Maybe I'm just missing it.

There are MUCH better ways to draw your circuit diagrams than what you did. They are very hard to follow.
Yes i tried with with "Logism" simulator for both of these circuits and i get the same truth table. So i guess both circuits what i made are right.

We just started learning digital electronics in class, the circuits wont be going harder anymore. Just some basic stuff how to convert from truth table to circuit and vice versa.

#### RBR1317

Joined Nov 13, 2010
631
Yes i tried with with "Logism" simulator for both of these circuits
If you are using Logisim then you should open the Combinational Analysis window, enter your values in the truth table, then let Logisim minimize the function & build the circuit.

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#### ronsimpson

Joined Oct 7, 2019
1,227

#### WBahn

Joined Mar 31, 2012
26,398
If you are using Logisim then you should open the Combinational Analysis window, enter your values in the truth table, then let Logisim minimize the function & build the circuit.
And then what do they do on the exam when they are given a similar problem and asked to do it themselves?

That approach is fine for someone using a tool to do the gruntwork, it's not fine for someone trying to learn the concepts.

#### WBahn

Joined Mar 31, 2012
26,398
Keep in mind that this is Homework Help, not Homework Done For You.

Having said that, an even better solution (assuming standard CMOS gates) would be to replace the AND and OR gates with NAND gates and change the NOT gate to an OR gate. As it is, this takes 18 transistors and has 4 gate delays. Making the changes reduces it to 16 transistors and 3 gate delays.

#### RBR1317

Joined Nov 13, 2010
631
And then what do they do on the exam when they are given a similar problem and asked to do it themselves?
And if you don't know how your tools work, then what good are you?

#### WBahn

Joined Mar 31, 2012
26,398
And if you don't know how your tools work, then what good are you?
So you would rather have someone that knows how to click a few buttons on a particular vendor's application and who then let's that tool's ability to do their thinking for them constitute "knowing" how to design a logic circuit that implements a desired truth table.

Again. What do they do when they see a similar problem on an exam? Write, "I have no idea, but since I memorized what buttons someone on the internet told me to press in Logisim, I deserve to get full credit for this problem."

#### RBR1317

Joined Nov 13, 2010
631
So you would rather have someone that knows how to click a few buttons on a particular vendor's application...
That would be a valid concern if one thought that knowing how their tools worked was limited to just understanding the user interface.

#### WBahn

Joined Mar 31, 2012
26,398
That would be a valid concern if one thought that knowing how their tools worked was limited to just understanding the user interface.
I've seen plenty of engineers that their understanding of an oscilloscope was how to press the Auto Set button and, if that didn't do what they needed, they were at a loss. Worse, they frequently were not capable of even recognizing that the setting the scope chose bore no resemblance to what they needed in order to answer the question they were tasked with exploring.

We hired a layout technician with 20 years of experience working for Intel, only to discover that her abilities were strictly limited to what their quarter million dollar per seat tool chain could tell her to do. She couldn't even recognize the layout of a transistor or layout a capacitor with our tools because it required HER to control the tool instead of the tool controller her.

Especially in an education setting such a digital design course, the tools should be used to VERIFY the solutions arrived at by the student. The student should be capable of doing every part of the design without any tool at all.

#### RBR1317

Joined Nov 13, 2010
631
We hired a layout technician with 20 years of experience working for Intel, only to discover that her abilities were strictly limited to what their quarter million dollar per seat tool chain could tell her to do.
So was this a case where the Human Resources Department provided you with the candidates you described you wanted, and you did not know how to use the tools available to you to make the proper selection?

#### WBahn

Joined Mar 31, 2012
26,398
So was this a case where the Human Resources Department provided you with the candidates you described you wanted, and you did not know how to use the tools available to you to make the proper selection?
As a company with five employees, including the president, we didn't have a Human Resources Department.

#### djsfantasi

Joined Apr 11, 2010
7,689
No one thought to ask if she was experienced in your tool? Were there no other questions that could be asked to at least get a hint of her skill level?

#### Beau Schwabe

Joined Nov 7, 2019
84
Just for "fun" here is what the LOGIC solution might look like in DTL (Diode Transistor Logic)

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