Can 555 be converted to a jk flipflop.

Discussion in 'The Projects Forum' started by KMK, Dec 17, 2010.

  1. KMK

    Thread Starter Active Member

    Feb 11, 2010
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    Hi guys, i am trying to build a tv remote controlled appliance switch as shown in the ink here http://www.circuitstoday.com/category/remote-circuits
    it mentions the use of a 555 & a CD 4017 ICs, the 4017 acting as a fliplop, whose state changes on the input pulse of the 555 monostable multivibrator.. i wanted to knowq if thisd same circuit can be designed using 2 555 ic, 1 for the multivibrater & the other as a j-k flipflop
     
  2. Wendy

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    Mar 24, 2008
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    Nope. It would be easier with transistors, gates, or diodes (combination of all three). Or, as you said, use a chip made for the function.

    It can barely make a 555 Bistable Multivibrator.
     
  3. KMK

    Thread Starter Active Member

    Feb 11, 2010
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    thanks fpr the information bill. I did check out that circuit of 555 bistable multivibrator, however that has problem that the toggle switch needs to be pressed to maintain the state. So i guess i'll have to stick to buying the made for purpose chip. thanks once again. Also it will eb useful if you could suggest any other ICs which can be used as j-k flip flops.
     
  4. Wendy

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    Pressed to maintain the state? I'm not sure if I'm misreading, or you misstated, but the toggle button needs pressed to change the state. The button is normally open, to charge the capacitor, when it is closed the flip flop toggles. Whether open or closed the state does not flip, it is the transition that does the trick. The 555 version (or any hysteresis inverting gate) is a true flip flop with analog roots. Transistors would be for a more complex flip flop.

    I've tried to figure out how to make it flip with a signal. My conclusion is it can be done, but it would take many more parts than is practical. Given the chip value for flip flops in general is 25¢ or less there is no sense to it.

    Try a 4027, for example, or a 7472, both are dual JK flip flops with set/reset inputs.
     
  5. shortbus

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    Sep 30, 2009
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  6. Ron H

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    He doesn't really need a JK. He just needs a toggle FF.
     
  7. KMK

    Thread Starter Active Member

    Feb 11, 2010
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    thanks for that information guys.. i will try to use the regular flipflop.. but if ti dosent work, will have to stick to using the chips.. will keep u guys updated..
     
  8. Wendy

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    Don't forget to debounce the switch feeding the flip flop.

    [​IMG]
     
  9. Ron H

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    I've got a way to change the 555 pushbutton toggle to one you can control with pulses, but it requires 2 transistors, 2 resistors, and 2 diodes. Personally, I would use a DFF or JKFF, but if anyone wants to see it, I can post it. I simulated it and breadboarded it. It worked.
     
    Last edited: Dec 19, 2010
  10. Wendy

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    I would be interested just to see the approach. With two transistors and a couple of diodes you could make a conventional toggle too. If the book doesn't have a transistor flip flop it might be interesting to add one.
     
  11. Ron H

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    OK, here it is. I tested it for 5V<vcc<12V. The diodes are to prevent base-emitter breakdown. If vcc<6V, the diodes are unnecessary.
    It worked in simulation for pulse widths as low as 1usec. I didn't have a simple way of generating a pulse that short for breadboard testing. The pulse frequency worked up to about 15kHz.
    Note that the schematic has fixed component values. The .ASC file, which is included for LTspice simulation, has the base resistors parameterized.
     
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  12. Wendy

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    That is indeed neat. I don't take it in at first glance, I'll have to study it a little while to understand it. Thank you.
     
  13. KMK

    Thread Starter Active Member

    Feb 11, 2010
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    hi guys, i have built the circuit.. seems working ok.. but i have 2 questions.. whats the need for debouncing.. secondly.. according to the original circuit diagram, pin 2 for the 4017 is out & 3 has an LED.. in my case .. the LED (D2) remains off when circuit is turned on..( output is high) but goes off when the outout is high.. did not understans this behaviour of the circuit..
     
  14. Ron H

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    Apr 14, 2005
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    You don't need a debouncer for the Appliance remote receiver.
    If you want the LED to be on when the relay is on, use the changes in the attachment.
    You also need a diode across the coil, to protect the transistor from the flyback voltage generated by the coil when the transistor switches off.
     
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