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Slow down this circuit's oscillation

Discussion in 'General Electronics Discussion' started by Jose Maria Rico, Jul 7, 2014.

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  1. Jose Maria Rico

    Jose Maria Rico

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    Jul 5, 2014
    Hello again, Electronics Point!

    Hope you all are doing just fine today.

    I have another circuit now. The main components are two flip-flops with basic on/off inputs, and two AND logic gates. The actual circuit I built is made up of BJTs, but drawing that diagram would be very time-consuming.

    Flip-Flop 1's output ALWAYS defaults to on when I turn on the circuit. That way, only one output will be on at a time. The problem with this circuit, as you might notice, is that if I send an input signal, the flip-flop output pins will oscillate on and off altenatively until the input goes low. I want to slow this oscillation down to about 0.5s or 0.8s, which is a little bit more than the time the input will be high for. The voltage source is +5V, from USB power.

    I assume the solution would involve adding a capacitor somewhere. I'm not very experienced with the use of capacitors. Any help is appreciated.

    Thanks in advance!

    EDIT 2: Maybe I could delay the On signals for each Flip-Flop for a little longer than the input high time. I don't know if building a delay circuit from jellybean components is easy, though.

    99.png
     
    Last edited by a moderator: Jul 7, 2014
  2. BobK

    BobK

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    Jan 5, 2010
    Instead of the lines going from the two Outputs to the inputs of the ANDs, try putting a resistor between them, then a capacitor from the input to ground. That should slow it to something on the order of RC seconds of on / off time.

    Bob
     
  3. Jose Maria Rico

    Jose Maria Rico

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    0
    Jul 5, 2014
    Hey, thanks for your response. Can you be a little more specific, please? You mean connecting the Outputs to the AND inputs via a resistor, and adding a capacitor to the single Input pin? Because that didn't work, and I think it made the input signal last even longer. Maybe I'm not understanding what you mean.
     
  4. Gryd3

    Gryd3

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    Jun 25, 2014
    The resistor will be placed between the output of of the Flip-Flop, and Input of the AND gate. Then a capacitor + lead will be placed along the same connection as the resistor and input of the AND gate. The capacitor - will be connected to ground.

    The idea here is:
    Flip Flop drives the line high which charges the capacitor though the resistor.. and when the charge gets high enough, the AND gate will fire.
    At this point the line will get driven low, which will discharge the capacitor to get ready to repeat.
    Do this on each side of the circuit with matching components and adjust the resistor or value of the capacitor to adjust how frequently your circuit flips and flops ;)
    If you use mismatched parts, your circuit may stay flipped longer than flopped.
     
  5. BobK

    BobK

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    Jan 5, 2010
    As Gryd3 said, like this: (excuse my amateurish painting)

    99new.png
     
  6. Gryd3

    Gryd3

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    Jun 25, 2014
    Reminds me of the day when I used Paint to draw things.. ;) It's almost like finger painting.
     
  7. davenn

    davenn Moderator

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    Sep 5, 2009
    I resent that remark ;)

    paint is awesome for circuit drawings, have used it for years and still do .... results look very professional ......

    [​IMG]


    cheers
    Dave
     

    Attached Files:

    Last edited: Jul 10, 2014
  8. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    Yeah, I like the clean and sparse look. I get the same thing with my old OrCAD/SDT III. And LTSpice makes pretty clean looking schematics too.

    Many of the modern schematic packages use lots of colours, and unnecessary clutter - they show dots where components join to lines, they show polarity indicators on every component, etc. It's the classic FSUI (fruit salad user interface). Someone should tell the creators of this software that clutter is distracting. It detracts from the important stuff.

    BTW the two polarised caps on the output of the negative regulator are upside down :)
     
    davenn likes this.
  9. davenn

    davenn Moderator

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    Sep 5, 2009

    hahaha in all these years, I never noticed
    This was not something I built, rather one of many boards out of a system that I reverse engineered.
    You can see by the date on the schematic 2003, it was a long while ago

    I will upload a revised version

    cheers
    Dave
     
  10. davenn

    davenn Moderator

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    Sep 5, 2009
    I have just noticed something else that doesn't seem right either ??
    the link from the left of the diode D1 on the output of U4a ( upper middle of drawing) going back to
    the right of the cap C13 on U4a pin2 input

    would this be a valid feedback loop or have I misread the circuit board trace ?

    cheers
    Dave
     
  11. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    No need to upload a corrected version mate :)
    It does look a bit odd, but I couldn't say whether it's right or wrong.
     
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