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

  1. xxxx

    Thread Starter New Member

    Dec 22, 2009
    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


    Jan 18, 2009
    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
    well stated MasterSnow
  4. DigitalLogician

    New Member

    Dec 20, 2009

    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 (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