Basic Digital logic circuit wrong sequnce flasher

Discussion in 'Homework Help' started by acurry023, Nov 16, 2015.

  1. acurry023

    Thread Starter New Member

    Oct 26, 2015
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    I am designing a circuit that requires a flashing LED when performing a wrong sequence. The correct sequence has 2 possibilities. The circuit has 8 switches that initialize D flip flops. The correct sequences are as follows; SW1, SW2, SW3, SW4, SW5 or SW6, SW7, SW8, SW1, SW2, SW3, SW4, SW5. The flashing LED is to be powered by a 555 timer which I already have configured. However for the life of me I cannot figure out how to get the timer to trigger off a wrong sequence. Can anyone help out with this? The requirement to complete the flasher is to use basic logic flip flops or some combination of and/or/nand/nor/xor gates.

    I am using multisim for the basic design and then building the circuit with actual hardware.
     
  2. absf

    Senior Member

    Dec 29, 2010
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    Can't understand what you are describing. Show us how the flip flops and 555 and switches are connected...

    Allen
     
  3. acurry023

    Thread Starter New Member

    Oct 26, 2015
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  4. acurry023

    Thread Starter New Member

    Oct 26, 2015
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    The timer on the right is the one that needs to trigger the wrong sequence. If everything is done right I can turn on switch 5 and the LED attached to the output will turn on. If done wrong it will not. The right sequence(s) is what I listed above, basically if I were to start the sequence with switch 2 then go to SW1, SW3, SW4, SW5 the LED connected to that timer should flash alerting me to a wrong sequence. I hope that helps. Thank you.
     
  5. absf

    Senior Member

    Dec 29, 2010
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    You can use the RST pin of the 555 to control flashing the LED3. When RST is high the LED should flash and vice versa.

    Try putting a NOT gate between output of U9A and RST of 555 and see if it works.

    Allen
     
  6. acurry023

    Thread Starter New Member

    Oct 26, 2015
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    In doing that the 555 still would need something powering the VCC. I tried running the output to the VCC of the 555 using the NOT gate and the light flashed until the right sequence is put in but it needs to be the opposite function. Any suggestions for that?

    Thank you for the help Allen
     
  7. acurry023

    Thread Starter New Member

    Oct 26, 2015
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    I should say that the LED needs to stay off until the wrong sequence is put in then needs to flash to indicate the wrong sequence
     
  8. absf

    Senior Member

    Dec 29, 2010
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    I did it this way as attached...

    Did you not separate out the Rst from the Vcc pin of 555?

    WRONG SEQ FLASHER2.PNG
     
    Last edited: Nov 17, 2015
  9. acurry023

    Thread Starter New Member

    Oct 26, 2015
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    Initially you were right I didn't not have it separated out from the VCC. I hooked it up the way you showed there and its the same as before it flashes until the correct sequence is input then it turns off. The project requires the opposite unfortunately, it should stay off until the wrong sequence is put in then turn on. Maybe I need to change the logic before then to get the desired output?

    Thanks again for your help adam I appreciate it
     
  10. absf

    Senior Member

    Dec 29, 2010
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    OK, since this is homework, I think I have given enough clues for you to continue tracking as where to get this logic signal.
     
  11. acurry023

    Thread Starter New Member

    Oct 26, 2015
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    Yes thank you again it was very helpful I appreciate your time
     
  12. WBahn

    Moderator

    Mar 31, 2012
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    This is a VERY bad design from a few standpoints, mostly because of the use of gated clocks throughout. Even if it works in MultiSim, it will almost certainly be nothing but a royal headache in an actual implementation.
     
  13. acurry023

    Thread Starter New Member

    Oct 26, 2015
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    We are running into that problem now. I had a feeling that would be an issue during hardware implementation. The project requires 8 different states to be shown by using switches. Would it be better to use them as the D input of the flip flops as opposed to the clock input for physical inplementation? I know this isn't a forum for giving answers but any suggestions are helpful
     
  14. acurry023

    Thread Starter New Member

    Oct 26, 2015
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    I already realize this is a bad idea so scrap that
     
  15. absf

    Senior Member

    Dec 29, 2010
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    You can google for "combination lock circuits using flip flops" on the interweb and get ideas from there.

    Are you allowed to use only d type flip flops?

    Allen
     
  16. acurry023

    Thread Starter New Member

    Oct 26, 2015
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    We can use any kind of flip flops and basic logic gate combinations. I think my biggest issue is I'm using the switches in the wrong manner. Unfortunately this is due tomorrow but I'm considering using the 555 as the master clock for the circuit and relying less on flip flops and integrating more basic logic gates into the circuit for the switches.

    Another twist is there has to be a ring counter attached to 3 LED once the proper switch sequence is initiated but I'm having a problem with what I believe is overdriving the LED so when they switch states they flicker which I'm trying to fix as well.
     
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