74192 garage counter

Discussion in 'The Projects Forum' started by angelajula, Apr 16, 2013.

  1. angelajula

    Thread Starter New Member

    Apr 16, 2013
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    Hi there. I am working on my capstone. We have created an up/down counter to attach to a sensor so as to count cars going into and out of a parking garage. While our circuit is working, I would however like the count up to stop at 120, and the count down to stop at 000. I would also like the reset button to reset to 120, if it is possible. Right now when it comes on in multisim, it starts the count at 999 and can roll up or down past 000/999. I have no idea how to successfully modulate the 74192 IC's. Any suggestions would be greatly appreciated. Here is a copy of my multisim circuit:[​IMG]
     
  2. tshuck

    Well-Known Member

    Oct 18, 2012
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    Instead of clearing the count on reset, load the counters with 120, or whatever number you want.

    Multisim is an idealized representation. The counts will come up in any state(count) unless it's taken care of in the device (not likely). So, don't count on coming up at 999.


    What do you mean by modulate the 74192 ICs? Do you mean multiplex?
     
  3. angelajula

    Thread Starter New Member

    Apr 16, 2013
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    I mean have a modulus or trunciated count of 120. As it is now, the count is to a full 999. To change the count means to create some kind of feed back to the input from the output of a flip flop or binary counting device like the 74192 and expect a specific count.
     
  4. tshuck

    Well-Known Member

    Oct 18, 2012
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    If all you want is a mod-121 counter, activate clear when count is greater than 120.
     
  5. BillB3857

    Senior Member

    Feb 28, 2009
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    Or, detect the count has reached 120 and disable further UP count inputs. I assume the parking garage has 120 spaces. If you really wanted to get fancy, a count of 120 could cause the 7 segment displays to flash FULL
     
  6. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    Since OP stated he wants the clear button to load in 120, I would assume 120 is the empty reading indicating capacity ready to be filled.
     
  7. crutschow

    Expert

    Mar 14, 2008
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    You can use a NOR gate to detect when all BO inputs are low (a NOR gate goes high when all inputs are low), which indicates all counters are at zero. You can use this signal to stop the count or do whatever else you want to do at when the counter reaches zero.
     
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  8. absf

    Senior Member

    Dec 29, 2010
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    Gathering all the informations from the feedbacks, I came out with the schematic attached.

    The random number at power-up was taken care of with the "power-up reset" circuit.

    But there is one problem I cannot understand. After power-up, though the counters show "000" at the outputs, the 3-input NOR doesnt inhibit the input (7408) of the down counter, until I presed the DOWN button once. Only then all the "BO" became LOW.

    After that if I pressed the UP button, the outputs of the counter becomes "990". I have to press the UP button 10 times for it to become "000" again. Is there any clue why this happens?

    Allen

    [edit] attachment removed [/edit]
     
    Last edited: Apr 17, 2013
  9. WBahn

    Moderator

    Mar 31, 2012
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    Err. I'm confused. Is this absf's capstone project or angelajula's capstone project?
     
  10. WBahn

    Moderator

    Mar 31, 2012
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    You need to clearly state the intended behavior. Consider this good practice for the report you probably have to prepare.

    You have some issues that your simulation is probably not going to reveal. As already pointed out, the counters will likely power up in just some random state, so you will have to either reset them manually or incorporate a power-on-reset. Then you pushbuttons are going to bounce causing all kinds of erratic behavior. You need to debounce them.
     
  11. absf

    Senior Member

    Dec 29, 2010
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    Sorry, I just couldnt resist.

    Hope this is not a homework project...:rolleyes::D

    Allen
     
  12. WBahn

    Moderator

    Mar 31, 2012
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    It's more than that, it's the OP's capstone project -- the BIG homework assignment!
     
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  13. absf

    Senior Member

    Dec 29, 2010
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    The schematic is removed.:D Luckily, Angela is not online at the moment...

    Sorry..
     
  14. WBahn

    Moderator

    Mar 31, 2012
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    Not a biggie, especially since your's had problems. And, hey, we've all done similar.
     
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