circuits

Discussion in 'Homework Help' started by MilkyTank, Jul 27, 2012.

  1. MilkyTank

    Thread Starter New Member

    Jul 27, 2012
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    PLEASE HELP i need to know how to decrement and increment 7segment using the 7447,74192 and LDR :confused:
     
  2. MrChips

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    Oct 2, 2009
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    You can begin by showing us your circuit that you are working on.
     
  3. WBahn

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    Mar 31, 2012
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    What is LDR?

    While we can provide some hints and suggestions, a big part of the point of the problem is for YOU to figure it out yourself; it's the struggle from which you learn, more so than the end result.
     
  4. MrChips

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    Oct 2, 2009
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    LDR - light dependent resistor.
    I assume the op wants to count objects going by.
     
  5. MilkyTank

    Thread Starter New Member

    Jul 27, 2012
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    this is the problem, i need to build a exit and entrance door and count the no. of people who enter the door at the same it decreases when somebody leave

    this is my tools:

    74192
    7447
    LDR
    7segment

    I dnt knw how to implement it :(:(

    please help
     
  6. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    Just have a look at the datasheets of the chips.
    Then you can see what signals are needed.

    If you want to determine the direction of the persons going in and out of the room,
    you will need TWO ldr's and make a circuit that can see the direction.

    Bertus
     
    Last edited: Jul 29, 2012
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  7. MilkyTank

    Thread Starter New Member

    Jul 27, 2012
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    thanks!!!!! but im confused about the connection between the 74192 to 7447 i hope you can help me
     
  8. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    I have taken the pinout diagrams from the datasheets:

    74192:
    [​IMG]

    7447:
    [​IMG]

    Bertus

    Note: sometimes the pins are called different.
    A can be called A0
    B can be called A1
    C can be called A2
    D can be called A3
     
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  9. MrChips

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  10. MilkyTank

    Thread Starter New Member

    Jul 27, 2012
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    how can i put out the buttons and change it to LDR
     
  11. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    Imagine a circuit that creates a puls on the up pin when a person walks along LDR 1 and then LDR 2.
    Imagine a circuit that creates a puls on the down pin when a person walks along LDR 2 and then LDR 1.

    What would be needed to create such a circuit?

    Bertus
     
  12. WBahn

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    Mar 31, 2012
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    What about when two people are passing the sensors at the same time in opposite directions? Virtually every combination, including missed and overlapping hits.

    The OP said that he was supposed to have separate entrance and exit doors, so just use one LDR on each door. You have to assume that people come through one at a time and that you only get one interruption per person (not one for each arm plus one for the torse and maybe a leg thrown in).

    [/QUOTE]
     
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  13. MilkyTank

    Thread Starter New Member

    Jul 27, 2012
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    can anyone give me some schematic about my problem. Im very confused iin how to do it :confused:
     
  14. WBahn

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    Have you tried building any of the circuits you've been directed to? Or the circuit that you yourself posted (which has some problems, but it's a start)?

    Start by trying to just make a single digit count up or down in response to button presses. Once you have that working (and I suspect you are going to have some problems getting to that point), then it becomes much easier to do the rest.

    So build just the one-digit version using buttons and tell us what happens when you try to use it.
     
  15. MilkyTank

    Thread Starter New Member

    Jul 27, 2012
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    i try to do it myself but it is not going smooth when it increase it always jump to far ex. 2 then 8 it always like that so that i try to see some other options
     
  16. WBahn

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    Mar 31, 2012
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    This is exactly what I expected you to see. I imagine that sometimes it jumps by, say, 5 and other times it jumps by, say 9.

    Have you ever heard of switch bounce? Well, that's almost certainly what you are seeing.

    So look up ways to debounce a switch. There are a few.
     
  17. MilkyTank

    Thread Starter New Member

    Jul 27, 2012
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    debounce switch?? like this??
     
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  18. MrChips

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    Oct 2, 2009
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    Debouncing an LDR is not the same thing as debouncing a mechanical switch.

    The dual NAND-gate circuit is the classic way of using a single-pole double-throw switch or push-button.
    (What you have there is an R-S flip-flop.)

    Except that circuit is incorrect. Both R1 and R2 should be pull-ups (to Vcc). 10kΩ is suitable for CMOS gates. For 74LS00 TTL gates, R1 and R2 should be around 1kΩ to 4.7kΩ.

    Debouncing an LDR sensor is a completely different story.
     
  19. MilkyTank

    Thread Starter New Member

    Jul 27, 2012
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    then how can i put LDR back to the line?? =_=
     
  20. MrChips

    Moderator

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    The problem with the LDR is more about logistics than debouncing, as WBahn pointed out in post #12.

    You can condition the signal from the LDR with a retriggerable monostable multivibrator such as a 74LS123 to produce an extended signal of a suitable duration.

    The problem is that it does not identify the direction of motion.

    Then there is the problem of two persons passing each other, one coming in and the other going out.

    On a first iteration basis, you will need at minimum, two sets of sensors, staggered in position. One sensor will detect later than the other. From this you can determine direction.
     
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