# Computer Logics and Digital Design

Discussion in 'Homework Help' started by divaremy, Mar 31, 2014.

1. ### divaremy Thread Starter New Member

Mar 31, 2014
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Design and simulate the circuit for the time based lighting control system. The required
system should power on the office lights at 7:00AM and power them off at 10:00 PM. For the
campus lighting, the system must power off the lights at 6:00 AM and power them on at 6:00
PM. Also requires that you design the circuit with a bypass switch which can be used to
bypass the timer just in case it fails. When the system is in bypass mode (bypass switch is on), it
should allow a switch to turn on and off the office lights. However, the outside campus lighting
should be powered on and off by the photocell (in your circuit, you can just use a switch to
simulate the operations of a photocell). Please note that when the bypass mode is deactivated, it
should not allow the switch or photocell to control the lights.

im suppose to do a simulation of a circuitry design. i dont know where to start. please help. i need it by thursday.

it should include truth tables, k-maps, boolean algebra, logic gates, decoder etc

Last edited: Mar 31, 2014
2. ### MrChips Moderator

Oct 2, 2009
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Moved from The Projects Forum to Homework Help.

3. ### WBahn Moderator

Mar 31, 2012
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You are given a list of things that you must include and you have no idea where to start on ANY of them?

If that is truly the case, then the place to start is at the beginning of the course next semester and, this time, pay attention.

If that is not truly the case, then begin by showing your best effort to get as far as you can. Start with the truth table by clearly listing the inputs to the system and the outputs of the system. Then list the states in which the system can be.

4. ### divaremy Thread Starter New Member

Mar 31, 2014
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is not that i dont know how to do them is figuring out the what the question is asking of me so i can know the inputs and outputs.

5. ### tshuck Well-Known Member

Oct 18, 2012
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What controls the lights? Those are your inputs. What is being controlled? Those are your outputs.

This is an automated lights controller with optional override of the automatic timings. If you don't understand it, read it again.

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6. ### WBahn Moderator

Mar 31, 2012
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Okay, let's list things individually:

1) Design and simulate the circuit for the time based lighting control system.

2) The required system should power on the office lights at 7:00AM and power them off at 10:00 PM.

3) For the campus lighting, the system must power off the lights at 6:00 AM and power them on at 6:00 PM.

4) Also requires that you design the circuit with a bypass switch which can be used to bypass the timer just in case it fails.

5) When the system is in bypass mode (bypass switch is on):

5a) it should allow a switch to turn on and off the office lights.

5b) However, the outside campus lighting should be powered on and off by the photocell

5c) (in your circuit, you can just use a switch to simulate the operations of a photocell).

6) Please note that when the bypass mode is deactivated, it should not allow the switch or photocell to control the lights.

Which of those items do you do not understand? What is your best guess at what each of these items means?

Try to restate the design objectives in your own words.

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7. ### divaremy Thread Starter New Member

Mar 31, 2014
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I know i'm not the smartest person when it comes to figuring out these situations. I understand what to do when i'm in class but when we get questions to do which pertains to real life events , its not so easy for me to figure out. All you guys being hard on me cause i'm female. I'm not a slacker and i have been researching but it all seems like a foreign language to me when reading about circuits. Anyways i really need your help cause this is due this week.

The thing is i got it with a group but they the one that slack off so i'm having to do it myself. Can you please help me do the truth tables then i will figure out the Boolean expressions, circuit, k-maps, etc. and that's the only thing i will ask for you to do for me. i will figure out the rest. i am attempting it, just so you know.

Last edited: Apr 1, 2014
8. ### shteii01 AAC Fanatic!

Feb 19, 2010
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You will need a counter. To count hours. A 4 bit counter counts from 0 to 15, that would be Midnight to 3pm, which is not good enough. So I suggest that you use 5 bit counter, a 5 bit counter goes from 0 to 31, you only need 0 to 23 because it will give you Midnight to 11pm, ignore 24-31.

You have two outputs. Let us call them Q0 and Q1. Q0 is for office lights. Q1 is for street lights.

So. Your counter counts from 0 to 7 (7am), at 7 the Q0 is 1 and it stays 1 until counter reaches 22 (10pm), when counter is 22 Q0 changes to 0. Counter counts to 23, then on the next change it returns to 0. This is your truth table for office lights, without any overrides.

tshuck has this article for the counter using flip-flops, I guess use 555 for the flip-flop clock signal. They did a 4 bit, you need 5 bit and from 5 bit table you only need values 0-23. http://forum.allaboutcircuits.com/showthread.php?t=82082

Last edited: Apr 1, 2014
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9. ### WBahn Moderator

Mar 31, 2012
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We aren't being hard on you (and until you said something I had no idea you were female). Assuming that we are being hard on you because you are a female merely reveals your prejudice. Get over yourself, we don't care.

But we do expect to see you put forth some effort. Aside from the fact that it is YOUR homework, we need you to give us a starting point. Seeing your efforts gives us a jumping off point to see where you are going wrong and lets us then try to steer you back on course. Saying that you're attempting it doesn't cut it -- show your attempt! It's that simple.

You say you can't understand what the problem is asking for. So I broke it out line by line and asked you to describe what your understanding of each part of the problem statement was. You've chosen not to do that. Well, how the hell can I help you better understand the problem when you won't make the effort to show what your level of understanding is?

I asked you to list the input and the outputs, as best you can. You've haven't even tried.

10. ### tshuck Well-Known Member

Oct 18, 2012
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While being a bit more complex toward the end, the modulus counter article may also prove to be useful.

To the OP, we don't know you. As WBahn said, we had no inkling that you were female until you said it. We are being hard on you because struggling is part of learning. Sometimes you need some direction as to what questions to ask (what Wbahn asked) to understand how to approach a problem.

We are willing to help you, but you must attempt the problem and show us what you are struggling with (how could we help you otherwise?).

11. ### divaremy Thread Starter New Member

Mar 31, 2014
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i was never taught up to 31 bits the teacher only showed us 0-15, 0-7 and 0-4.

12. ### divaremy Thread Starter New Member

Mar 31, 2014
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I'm sorry for what oi said. its just that this isnt the first site i have tried to get help and everyone keeps being so mean about it.

I would never want someone to do all my work for me cause then whats the point of going to school, i wont learn anything and wont be able to function when i get a job.

13. ### shteii01 AAC Fanatic!

Feb 19, 2010
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All I can say is that I was taught the principals and I practiced on 2, 3 and 4-bit examples. Therefore I can do any bit count. If you know the principals, then you should be able to do 5-bit truth table, or google it and teach yourself since you already know 2, 3 and 4-bit truth tables.

14. ### WBahn Moderator

Mar 31, 2012
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5,755
Hopefully, they showed you 0-3 (2 bits), and then showed you how to expand that to 0-7 (3 bits) and how to expand that to 0-15 (4 bits), emphasizing how what you did to expand from 3 to 4 bits was essentially the same thing that you did to expand from 2 to 3 bits. The idea is for you to then generalize on this by seeing if you can expand that to 5 bits and then to 6 bits. At that point, doing N bits shouldn't be a problem.

So, if this is a sticking point, go back and see if you can see the pattern in going from 2 to 3 to 4 and then see if you can get to 5.

15. ### WBahn Moderator

Mar 31, 2012
20,229
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Engineering isn't for the faint-of-heart. It is a field in which incompetence, neglect, or carelessness can quickly cost hundreds or thousands of people their lives. So the practitioners of this art tend to be pretty ruthless with their own -- and expect similar treatment in return. It definitely isn't for the thin-skinned.

But you seem to think that it's okay to ask for someone to do part of your work for you. That isn't going to fly. We will try to help you struggle and fight your way along doing it for yourself -- but we won't do ANY of it for you.

The learning is in the struggling.

Consider that your instructor worked examples and the book worked examples, yet something hasn't clicked and you can't do the first step on your own. Well, having someone else do that first step for you isn't going to make it magically click and, as a result, you won't be able to do the first step the next time, either. It's when you have to fight with it and beat it into submission that, as some point, you'll have that 'Aha!' moment and wonder why it was ever so difficult. It's the way we learn most things.

Last edited: Apr 2, 2014

Mar 31, 2014
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17. ### tshuck Well-Known Member

Oct 18, 2012
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First off, why are you making a 4 bit counter? The maximum count is (2^4)-1 = 15, as you noted, but we need to count 24, no? In which case, you need log(24)/log(2)~=4.585, rounded up to 5, means you need at least 5 bits to represent a 24 hour day.

Second, you're K-maps are reduced incorrectly. If you look at the thread that shteii01 linked to, I went through the steps in designing a 4-bit counter and what the results are.

You should show what's grouped together (try highlighting the cells that you are grouping so we know what you are trying to do), that way, we can see where you might be going awry...

18. ### divaremy Thread Starter New Member

Mar 31, 2014
26
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that clock was done before you told me about the 32, im redoing it, i just wanted to know if i was on the right track with that one.

19. ### tshuck Well-Known Member

Oct 18, 2012
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675
...close, read the thread on counters if you want to understand the underlying design, and ask questions if you don't understand any part of it.

20. ### divaremy Thread Starter New Member

Mar 31, 2014
26
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is the truth table done correct? is it only the kmaps not correct?