# Help!!

Discussion in 'Homework Help' started by xxxx, Dec 22, 2009.

1. ### xxxx Thread Starter New Member

Dec 22, 2009
1
0
I need help with a project..!! =X I have absolutely no clue how to do this especially drawing the logic diagram/circuit! AND I just need help with the N-S not the E-W

Figure 4-50 shows the intersection of a mainhighway with a secondary access road. Vehicle-detection sensors are placed along lanes C and D (main road) and lanes A and B (access road) These sensor outputs are LOW (0) when no vehicle is present and HIGH (1) when a vehicle is present. The intersection traffic light is to be controlled according to the following logic:

1) The East West light will be green whenever both lanes C and D are occupied.
2) The East West light will be green whenever either C or D is occupied but lanes A and B are not both occupied.
3) The North South light will be green whenever both lanes A and B are occupied but C and D and not both occupied.
4) The North South light will be green when either A or B is occupied while C and D are both vacant.
5) The East West light will be green when no vehicles are present.

I need the Boolean Expression which i go t ABD'+BC'D+ABC'+AC'D'.. is it right? and the LOGIC DIAGRAM!! please would someone help me? =/

2. ### MasterSnow Member

Jan 18, 2009
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Hi xxxx,

So you need help with formulating the boolean logic for the N-S controller and drawing the logic diagrams for both of them (which I assume means the logic circuits with AND, OR, and NOT gates).

Since you said that you have no clue how to do this, I'll tell you a basic strategy that I think works (please forgive me if I'm repeating things that you already know). It seems to me that you want to set up two logic equations - one for N-S and one for E-W.

You'll want to look at your list of control directives and see which ones cause change to the N-S and which ones cause change to the E-W. Those are like boolean expressions written out in English. An English "either" and "or" implies use of the logic function OR; similarly, "both" and "and" imply use of the AND logic.

Now look at number 3 in your list. This is what I believe the expression to be for that: ABC'D'. You'll add more terms to this equation for other N-S directives. Then you can see if any terms are redudant and remove them.

When drawing the logic circuit, start with each term and move upwards. For example, suppose you had AB + CD. You'd have all your inputs A - D, which A and B going into an AND, C and D going into an AND, and then those outputs going into an OR.

I hope this helps and isn't too verbose. Best of luck.

3. ### VoodooMojo Active Member

Nov 28, 2009
495
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well stated MasterSnow

4. ### DigitalLogician New Member

Dec 20, 2009
5
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xxxx,

Perhaps I could help you more if I could see the figure you are referring to. If you want to draw and test the diagram online you can use the online circuit board at http://www.teahlab.com/ (click on "circuit board" and then scroll down). I use it extensively both for my own work and to answer questions on forums.

If you still need help, load the figure and we can go from there.

Good luck