Discussion in 'Homework Help' started by brahms, May 9, 2014.

1. ### brahms Thread Starter Member

May 9, 2014
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Hi, i'm a newbee here and on electronics world. Please help me to create a Combinational circuit with 4 inputs and the output is up to you, just by using TRANSISTORS. My prof said we can make security alarm or circuit that perform mathematical operation with these. But we don't seem to know how

A schematic diagram is all I need. Thanks, Cheers!

2. ### tshuck Well-Known Member

Oct 18, 2012
3,531
675
Just pick something and implement it. If you don't know how, that is another matter.

What's wrong with a 4-bit lock?

3. ### brahms Thread Starter Member

May 9, 2014
32
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I've made something, just for reference in further making this project. A 4 input NAND gate using transistors and have 2 led outputs. But I think that's not enough to satisfy the wants of my teacher.. I'm so out of ideas, we we're just on the basics and then this project. I'm new in this forum and didn't expect to get a reply this fast

4. ### tshuck Well-Known Member

Oct 18, 2012
3,531
675
There is pretty much always someone hanging around here (not always meaning quick replies though).

It seems your professor wants you to make something with a specific application, as opposed to a generic use device like the 4-input AND gate.

It seems hard at first, and granted, it is, but once you have an idea of what to make, the process is methodical and relatively straightforward.

5. ### brahms Thread Starter Member

May 9, 2014
32
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Yes, but can you possibly give some ideas? I know how to implement the simple logic gates using transistors with 2 inputs and LED's as outputs. I'm not that knowledgeable though, so forgive me if I can't understand somethings

Thanks for the replies, chuck? (is it?)

6. ### tshuck Well-Known Member

Oct 18, 2012
3,531
675
Okay, here are a few possibilities:
-Combination lock(outputs a 1 when a certain 4- bit value is input)
-2-bit multiplier
-4-bit squarer(?) = x^2
-2-bit comparator (determines whether A>B)

...to name a few...

Nope, but you're welcome nonetheless.

brahms likes this.
7. ### Alec_t AAC Fanatic!

Sep 17, 2013
5,979
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Good luck with the project, but note that the mods will probably move this thread to a different section, since it does not provide feedback about the site.

brahms likes this.
8. ### brahms Thread Starter Member

May 9, 2014
32
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Perfect suggestions! This will do i think.
Can this be made into a real project? Hehe, if we are about to do it in a PCB, what should be used to indicate the outputs? So sorry man, i'm in the clouds

9. ### brahms Thread Starter Member

May 9, 2014
32
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Oh, i didn't realize it hehehe sorry. I guess, i'll post it again.
I'm not that familiar here, my first time to post a thread. Thanks for correcting!

10. ### tshuck Well-Known Member

Oct 18, 2012
3,531
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When you say PCB, what do you mean? At your level, many people have a hard time knowing the difference between a breadboard, protoboard, stripboard, a printed circuit board, etc.

Are you expecting to solder components to a board?

Either way, LEDs are, typically, the go to for indicating logic levels (wire them slightly different and you can indicate a active-low output too!).

11. ### brahms Thread Starter Member

May 9, 2014
32
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Printed Circuit Board.. Yes, we will be soldering the components to a board I've posted this in the wrong forum. hahah sorry. I'm starting to feel shy of you..
More questions,
2 bit multiplier and 2 bit adder are just like AND and OR gates right? (from their corresponding truth tables, the outputs shown are the same?)

12. ### tshuck Well-Known Member

Oct 18, 2012
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675
I'm talking about adding/multiplying two 2-bit numbers. This will require a few gates...

13. ### brahms Thread Starter Member

May 9, 2014
32
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Yes.. if it's a 2-bit adder, then there is A B C D right? hehe correct me if i'm wrong,. 2 bit numbers are 0 and 1 right? or its 00 and 01?

14. ### brahms Thread Starter Member

May 9, 2014
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This is a NAND gate, i think. Is this correct?

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15. ### tshuck Well-Known Member

Oct 18, 2012
3,531
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It sounds like you have a few misconceptions, those will go away with exposure, so don't worry too much.

A 2-bit number has two bits - each bit has two possible states 0 and 1, so a 2-bit number has the possible options of 00, 01, 10, and 11, representing decimal 0, 1, 2, and 3, respectively.

So multiplying two 2-bit numbers means you need to be able to do up to 3*3=9.

How you label your variables is up to you. If I was operating on two 2-bit numbers, I would probably choose variables like a1,a0,b1, and b0 for my inputs, but that's me...

16. ### brahms Thread Starter Member

May 9, 2014
32
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Oh... yeah, right =)) I get it now. Thank you!

I've done some googling and most of the people use a1,a0,b1,b0 as variables for the inputs. How will these be shown using LEDs?

17. ### tshuck Well-Known Member

Oct 18, 2012
3,531
675
Since these are inputs, their states are set by a switch (probably the most reasonable choice, anyway). It's the outputs that you want represented using the LEDs. How they are connected depends on your design.

What kind of logic are you to design with?

18. ### brahms Thread Starter Member

May 9, 2014
32
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If it's an adder, then it doesn't mean that i'm going to use ONLY OR gates for the circuit? I only know the basics.. so...

19. ### tshuck Well-Known Member

Oct 18, 2012
3,531
675
It means that you will have to use the gates you know of to bills a more complicated device.

You first need to start with the behavior of the device - you would lay out a truth table showing all the possible combinations for the inputs and what the corresponding outputs would be for the function you wish to implement (e.g. adder).

Then you'd typically reduce the logic using Boolean algebra/K-maps and implement the reduced logic using the techniques you've learned.

20. ### brahms Thread Starter Member

May 9, 2014
32
0
Okay.. =)

I know how to reduce the logic using Boolean/K-map, but i find K-mapping easier. Can you please enlighten me more about this 2 - bit adder? And do you think it's the one that is suited for my level? Hehehe, if no. Please recommend a new concept