555 timer and flip flop project help needed

Discussion in 'Homework Help' started by Tan Min Lee, May 13, 2015.

  1. Tan Min Lee

    Thread Starter New Member

    Dec 16, 2014
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    I need to do a mini project using flip flop and 555 timer. The 555 timer must act as a clock signal. Everyone cannot have the same idea and project that can be search online like digital dice, clapping switch have already been taken. Please help me.
     
  2. Ramussons

    Active Member

    May 3, 2013
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    How about counters, dividers, GO/NO GO logic based on time ......
     
  3. DickCappels

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    Aug 21, 2008
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    A coin toss simulator.
    Use this circuit as the basis, but leave the LED off of the NE555 output. Connect one LED with resistor to the Q output of the first flip-flop and connect another LED to the NOT-Q output. Instead of using the second flip-flop, tie its inputs to ground.

    Make the oscillator operate at a high speed so that it looks like both LEDs are on at the same time. Connect a button connected from the trigger input to ground. When the button is pressed and held, only one LED will be on, which would be the indication of heads or tails.

    [​IMG]
     
  4. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
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    Chase lights using the flip flops to construct a shift register.
     
  5. WBahn

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    Mar 31, 2012
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    Aside from handing the TS a ready-made project, I don't agree that it will simulate a coin flip to begin with -- unless I'm missing something. It's a counter circuit, which means that all four possible states will be available so sometimes both LEDs will be on and sometimes both will be off.
     
  6. Tan Min Lee

    Thread Starter New Member

    Dec 16, 2014
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    How about something like this? Will it work?
     
  7. WBahn

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    Mar 31, 2012
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    I thought you were NOT supposed to just grab something from the internet and build it.

    Aside from that, this is a bad design. Aside from the floating clock input, which is a BAD idea, particularly if this is a CMOS part, the other FF in the package is apparently left floating, which is another BAD idea. Also, what is the function that the FF implements if pins 3 and 14 are both tied LO?
     
  8. Tan Min Lee

    Thread Starter New Member

    Dec 16, 2014
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    Im kinda lost now. We can steal ideas from the internet but the ideas cannot clash with other people. Cause currently we're just in our first year and all these is kinda new. Can you please help and explain more? Any other ideas?
     
  9. WBahn

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    Look at the data sheet for the 7473 (just Google "7473" and you'll get lots of hits -- the Fairchild datasheet will probably be high on the list) and see what the outputs do when both the J and K inputs are held LO.

    Leaving inputs on digital parts floating is a bad idea, particularly if the device is CMOS. With a floating gate, you have an undefined input level which can not only lead to unpredictable behavior, but also to "shoot-through" currents than can damage the part. In that circuit, you want to install a high value resistor between the clock pin and one of the rails. Tie it to ground if it's a CMOS part and to Vcc if it's TTL (this just conserves a bit of power, since TTL will "float HI").
     
  10. Papabravo

    Expert

    Feb 24, 2006
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    I suppose stealing and cheating are the new normal. Is that what I'm hearing? How do you ever expect to succeed if that is your attitude?
    Did you see the pictures of parents and relatives in India climbing the sides of a building to pass answers to the students taking exams?
    https://www.google.com/search?q=Exa...niv&sa=X&ei=iHBTVc_-L4iXyATNuIBg&ved=0CB0QsAQ
     
  11. WBahn

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    I can see a first-year course allowing students to find circuits on the internet and just build them to get experience building circuits and debugging the implementations (such as wiring errors). Given how many poor designs are out there, I would prefer that the instructor provide a set of projects designs that are of the right scope and of proven design, but that's me.

    On a separate note regarding the cheating in India, it never ceases to amaze me since I first learned of out systemic it is there about three years ago (thanks to a post here on AAC). I've talked to a number of Indian professors since then that have shed a lot of light on what has led to this. I still find myself shaking my head.
     
  12. Papabravo

    Expert

    Feb 24, 2006
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    Well the difference between properly guided and motivated students and those cast adrift to fend for themselves is truly amazing. Another interesting thing about those outstanding projects is that even with the paper in hand it would be difficult for the cheaters to copy and pass it off as their own.
     
  13. DickCappels

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    Aug 21, 2008
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    That is exactly what I hoped to describe. Follow WBahn's advice and ground all of the inputs of the other flip-flop in the package.

    @WBhan, In some schools (not in the U.S., AFIK), copying a project from the internet is considered good enough to be a Senior project. About the four states, I suggested she ground all of the inputs on the second flip-flop and only have LEDs on the output of the first.
     
  14. WBahn

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    Mar 31, 2012
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    Ah, I didn't read your post closely enough. I thought you were just removing the first LED and using the other two as is -- skimmed things too quickly.

    Copying from the internet may not be good enough for a Senior project in the U.S. today, but I foresee a day in the not too distant future....
     
    DickCappels likes this.
  15. JoeJester

    AAC Fanatic!

    Apr 26, 2005
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    WBahn,

    Ok fess up ... is it as bad as it seems?
     
  16. WBahn

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    If anything, it's worse.
     
  17. JoeJester

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    Apr 26, 2005
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    Well, I hope those that answer here will reflect upon that when answering inquiries. It's been a few years since those rules were generated. I intend to fully stand by them. I know you will.
     
  18. DickCappels

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    Aug 21, 2008
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    The circuit of post #6 has the correct form, but the details are wrong.

    1. Operate it from 5 volts, not 6 volts because this is TTL and needs 5V ±5%. If you are using CMOS instead, check the voltage rating for that particular part.

    2. Pin 3 and 4 the K an J inputs respectively need to be tied to +5V in to allow the device to toggle.

    3. The LEDs will not conduct as they are shown in the circuit. Connect one cathode of each LED to Q and NOT-Q and the anodes of each LED to a resistor (start with 470 ohms), the other end of the resistor going to +5V.

    4. Put a 0.1 uf capacitor between pins 4 and 11 (Vcc and GND respecitively).

    5 . Put a 100 uf capacitor across the power supply pins near the NE555.
     
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