# Building 3 To 8 Decoder On Multisim

Discussion in 'Homework Help' started by x56ahmet56x, Apr 20, 2015.

1. ### x56ahmet56x Thread Starter New Member

Apr 20, 2015
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0
Hi everyone. I need help with my homework. I need to design the inside of a 3 to 8 decoder with using logic gates. So far i made something but it didn't fully work. I mean not all when i give inputs as "000" it does make the first output on but when i try "100" its not give any output. I give the file below.

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2. ### WBahn Moderator

Mar 31, 2012
18,089
4,917
What the heck is an ms12 file? I'm guessing it's a Multisim format? I guess that's fine if you want to restrict yourself to people that have Multisim AND are willing to open files from strangers.

Since the problem seems to be more related to the design of a 3-to-8 decoder, how about posting a screen shot of your best attempt to solve the problem to date, including your truth table and your reduction to the logic you used to implement it?

3. ### x56ahmet56x Thread Starter New Member

Apr 20, 2015
4
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Sorry about that. To be more explanatory what i want is using only and or may be nand gate and build a decoder itself. When the inputs are "000" then the first output of 8 output must be glow and when the inputs are "001" then the second output of 8 output must be glow and so on until the last output. this is what i did.
and the mechanism suppose to be like this

4. ### WBahn Moderator

Mar 31, 2012
18,089
4,917
So when a switch is open, what voltage level is the input of a gate at?

Why are you using 20V?

5. ### x56ahmet56x Thread Starter New Member

Apr 20, 2015
4
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well to be honest I'm not familiar with designing circuits (i'm a computer engineering student at second grade) and they just gave this homework so we can research and design something. so i just need a circuit (doesn't matter what is the voltage) that could be used as a decoder.

6. ### WBahn Moderator

Mar 31, 2012
18,089
4,917
I'm assuming that the indicators attached to the output of the AND gates is a Multisim part that displays logic levels. If so, then put one of them on all six of the bus lines that are used for the inputs to the AND gates and verify whether those lines are behaving as expected.

The problem may be that you are using an analog supply for your signals and you need to use a digital supply. Also, how is your ground being referenced?

7. ### dl324 Distinguished Member

Mar 30, 2015
3,384
653
Think about the questions WBahn asked and answer them. They'll guide you to a solution.

I assume you've checked your Boolean algebra and have verified that it "should" work.

8. ### x56ahmet56x Thread Starter New Member

Apr 20, 2015
4
0
Thanks for help 'WBahn' and 'dl324'. I found the problem. Some of the probe aren't connected with circuit. I connected them and it solved.