LED Roulette Project - Simulation/Breadboard Help

Discussion in 'Homework Help' started by Ruairí Monahan, Jan 3, 2016.

  1. Ruairí Monahan

    Thread Starter New Member

    Jan 3, 2016
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    Hello everyone,
    This is my first post and hopefully not my last as I hope to reply and help those in need as I expand my own knowledge on circuitry (beyond that of fallout 4!).
    I have a project which is due in a few weeks time (fast tracked course as we only received the assignment recently) and for my project I have chosen an LED roulette wheel with touch sensitive switch, which when triggered will produce the LEDs to light up one after the other until it stops on one random LED. I have researched several circuits (creating all of them on MultiSIM, which none of them worked exactly) and decided to focus on one particular circuit as I had the most success using MultiSIM (The LEDs spun once and the circuit crashed). [​IMG]
    The above circuit is the one I chose. As this is a BTEC I cannot ask for help from the tutor however I am stuck in the mud right now (and usually I am quite good at building circuits both virtually and practically) as I cannot get the virtual simulation to work but more importantly I cannot get the circuit to work on a breadboard. Does anyone have any suggestions? I would really appreciate some help here and even a diagram of the breadboard just to help would be great also!
    [​IMG]
    Obviously I do not want someone else to do my project for me however a diagram or two would really help me as I am quickly running out of ideas and who better to ask than the experts?
     
  2. ISB123

    Well-Known Member

    May 21, 2014
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    Show us the picture of your breadboarded circuit.
     
  3. Ruairí Monahan

    Thread Starter New Member

    Jan 3, 2016
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    I can upload a picture of the breadboard tomorrow as I have it stored in class although I hope it is not too much of a mess of wires for you to see! Cursing myself for not taking pictures when I built it!
     
  4. ISB123

    Well-Known Member

    May 21, 2014
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    Take the picture from top view so we can see more clearly. Do you understand how the circuit works?
     
    Last edited: Jan 3, 2016
  5. WBahn

    Moderator

    Mar 31, 2012
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    MOD NOTE: Moved to Homework Help from Projects.
     
  6. WBahn

    Moderator

    Mar 31, 2012
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    We need to know what the guidelines are that you are supposed to work within. You say that you are not allowed to ask the tutor. That strongly suggests that asking for help from anyone else is not allowed, either.
     
  7. Ruairí Monahan

    Thread Starter New Member

    Jan 3, 2016
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    Sorry WBahn, thanks for getting me in the right place! Sorry it says we are allowed to receive help and guidance from outside sources and we are encouraged to "justify our choices" from many mediums such as simulations, personal observations (help from other class mates) and the use of forums as well as apps etc. This thread will be submitted in my final report.
     
  8. WBahn

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    Mar 31, 2012
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    Thanks for the explanation.

    At first glance it appears that the circuit you have shown let's the 555 run as long as the touch sensor is being touched (touching the sensor provides a path to ground for the base current and charges the 1 uF capacitor to about 9V). Once the touch sensor is released the cap will discharge through the base resistor giving about a 1 second time constant. So somewhere in the range of two to three seconds after being released, the 555 will stop running.

    Is that how it is behaving? Is that the behavior you are looking for?

    I would be tempted to just let the 555 free run continuously and use your touch sensor to set a flip flop that stops the counter from counting. But there are many ways to approach this.
     
  9. Colin55

    Member

    Aug 27, 2015
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    "Once the touch sensor is released the cap will discharge through the base resistor giving about a 1 second time constant. So somewhere in the range of two to three seconds after being released, the 555 will stop running.
    I would be tempted to just let the 555 free run continuously and use your touch sensor to set a flip flop that stops the counter from counting. "

    You missing the whole point of the 555. And you don't understand how the BC557 works.
    This circuit has been stolen from my website and the 555 gradually slows down and the LEDs stop on a number,just like a roulette wheel.
     
  10. DickCappels

    Moderator

    Aug 21, 2008
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    Before you go much further with the breadboard, you should put a .01 uf decoupling capacitor between NE555 pins 8 and 1, and a 0.1 uf capacitor between the CD4017 pins 16 and 8. Place the capacitors as close to these pins as possible and use short leads.

    Explanation:
    The NE555 shorts out the power supply twice a cycle as the output stage changes state, the resultant current pulses can cause "glitches" and those glitches can affect the circuitry inside the CD4017. The .01 uf on the NE555 supplies current for during the crossover during state changes on the NE555 output and the 0.1 uf on the CD4017 provides a more constant power supply impedance for circuitry inside the CD4017. The power supply pins are part of the logic circuit.

    Without those two capacitors you are inviting strange behavior.
     
  11. WBahn

    Moderator

    Mar 31, 2012
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    I most certainly did not steal this circuit from any website -- I'm not the one that posted it. I also have not analyzed it (you might note the phrase "at first glance").

    With the comment that the 555 gradually slows down, then I will assume that as the transistor is shut off by the rising base voltage that is progressively starves the 555 timing resistor of current, effectively making it look like an ever increasing resistance and thus resulting in a slowing frequency.

    It would still seem (and still only using a quick glance) that the circuit would operate at "full speed" only as long as the sensor is being touched and that, once released, it would then start the slowing process. But apparently this is wrong since, as you say, I don't know how a 555 timer works or a PNP transistor works. So could you describe how the circuit IS supposed to behave?

    And, if you don't want circuits to be stolen from your website, then perhaps you should not post them where the entire world can see them and grab them.
     
  12. Colin55

    Member

    Aug 27, 2015
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    All my circuits were stolen by 555-timer-circuits and they put their name on the circuit.
    They have not responded to my requests to remove their name from my circuits.

    It takes a lot to upset a 4017.
    10n and 100n will do nothing.
    The mere fact that the parts on a breadboard are very loose, countermands your retirement.
    The only thing that really affects the 555 is 10n on pin 5 but since we are using random pulses anyway, the improvement will not be noticed.
     
  13. ISB123

    Well-Known Member

    May 21, 2014
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