counter using j-k flip flops(7476) and debouncing switches using 7414 problem

Discussion in 'The Projects Forum' started by Omar123, Dec 23, 2012.

  1. Omar123

    Thread Starter Member

    Dec 23, 2012
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    I've built a counter using j-k flip flops and i've denounced the input switches( the one going in an the one going out) using schmitt trigger 7414
    so my project is about counting people for eg going inside a supermarket and the ones leaving the supermarket(both are done by the denounced switches)
    and i subtract them with a 74283 4 bit full adder to see how many clients are left inside the market. to denounce the switches i've built an RC network.
    10k pull-up is connected to 5v and another 1 k is connected to the input of the schmitt trigger and parallel to that a 10micro farad capacitor. the input of the switch come from the 1k resistor and from the other side of the switch to ground.. i'll show you the circuit i've built attached to the document.
    the problem and the only one(all the circuit is working properly as expected) is that when i want to leave 8 people, sometimes 4 and 8 binary leds are tuned on instead of of the 8 bit is on and sometimes it works well.why? what is wrong ?do i need a 15 micro farad capacitor?

     
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    Last edited: Dec 23, 2012
  2. absf

    Senior Member

    Dec 29, 2010
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    I dont understand what are you saying here...

    When 8 people left, your 4 LED indicating "8421" should light up "8" but instead it lights up "4". Is that what you're saying?

    Allen
     
  3. BReeves

    Member

    Nov 24, 2012
    412
    64
    First thing I would do is add a bunch of bypass caps.. The sticky on bypass caps in the general section is a good place to start.
     
  4. Omar123

    Thread Starter Member

    Dec 23, 2012
    36
    0
    when 8 people left led "4" and led "8" light up instead of only "8"
     
  5. Omar123

    Thread Starter Member

    Dec 23, 2012
    36
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    I've already put 10microFarad into the input of the shmitt gate
     
  6. Audioguru

    New Member

    Dec 20, 2007
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    896
    That is the messiest tangle of wires I have ever seen.
    If the extremely old circuit is made neatly on a compact pcb with important supply bypass capacitors (0.1uF ceramic for each IC) then it might work properly.

    Oh, the outputs of the counters are lighting the segments in your display but an old TTL IC cannot always produce a valid logic high if it drives an LED.
     
  7. Omar123

    Thread Starter Member

    Dec 23, 2012
    36
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    The circuit is working 100% properly but my only problem is that sometimes when 8 are going out.."4" and "8" LEDs are lighten up instated of only 8. I didn't understand what do you mean by old TTL/IC
    And where the 2 0.1uF ceramic must be connected? On the input of the schmit trigger? And btw the 7 Segment with the 7447 are working fluently. Thanks
     
  8. absf

    Senior Member

    Dec 29, 2010
    1,492
    371
    No, your circuit is not working 100%. If it were, it shouldnt give you intermittent problems like lighting up wrong LED.

    http://en.wikipedia.org/wiki/Decoupling_capacitor

    The 10uF caps in your circuit are not bypass or decoupling caps. You need one 0.1uF cap connected to each TTL chip between the Vcc and Gnd. The lead should be as short as possible.

    Allen
     
    Last edited: Dec 23, 2012
  9. Omar123

    Thread Starter Member

    Dec 23, 2012
    36
    0
    Then what is 10 uF doing in my case? And you are suggesting me adding a 0.1uF ceramic capacitor to reduce noince/high impeadance of the circuit..how many do I need? The input of my switches are the clocks of the 7476.. Do I need to put a
    0.1uF in the 1st clock of all 7476's so a total of 4? Or the + leg to the vcc and the - leg of cap to the ground for each 7476?What about the 7447? Does it need a decoupling cap? Also do I need to replace my 10 uF by 0.1uF ceramic? I forgot to tell u guys that my input(the ones going inside) is working well except for my switch going out. Are the values of the RC network good? Thanks for your time
     
    Last edited: Dec 23, 2012
  10. Audioguru

    New Member

    Dec 20, 2007
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    7476 ICs were introduced about 46 years ago. They used a high supply current and the supply must be only 5V. LS7476 ICs came a little later, used less supply current and operated at higher speeds. Cmos came later and replaced most TTL in new designs.

    I stopped using old TTL ICs about 36 years ago and have used Cmos ever since. I wonder why your teacher does not use Cmos.
     
  11. Omar123

    Thread Starter Member

    Dec 23, 2012
    36
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    This course is only for TTL we'll Gonna study CMOS later..very helpful infos but I need help using this type of IC's where do I need to put the 0.1 micro farad (drlecoupling) ceramic capacitor? Between the vcc(+leg of cap) and the ground of every 7476(-leg of the cap) of between the clock and the ground of all 7476's making a total of 4 caps. What do I need to do for the 10 micro farads caps? Replace them with a 0.1 also? And finally do the 7447 need any decoupling cap? I'll show u in a pic how I connected the input switches to the Schmitt trigger.
     
  12. Omar123

    Thread Starter Member

    Dec 23, 2012
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    here is the configuration i used to denounce the switches...btw i am using a 6v supply
     
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  13. MrChips

    Moderator

    Oct 2, 2009
    12,421
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    You are doing a whole bunch of things wrong.
    You must use 5V supply, not 6V.
    Remove any capacitors between CLOCK and GROUND.
    Put 0.1μF capacitors between Vcc and GND of each chip.
    Put one 10μF-100μF between Vcc and GND.
    It is not a good idea to drive LEDs from the same outputs that also drive the next clock. Use the unused Q' output instead.
    You don't need those 10kΩ pullups. Connect the pushbutton across the capacitor.
     
  14. Omar123

    Thread Starter Member

    Dec 23, 2012
    36
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    where do i need to put("Put one 10μF-100μF between Vcc and GND")this 10μF?On the main vcc and ground rail? do i need to remove my 10μF capacitor from the inputs of the schmit trigger? and does the schmitt triger/7447/74283 need a decoupling cap?
    can i use this type of 0.1μF?
    http://www.google.co.uk/imgres?imgu...bnw=135&ei=SW3XUIPZB4jdtAaKpYCwBw&um=1&itbs=1
     
    Last edited: Dec 23, 2012
  15. Omar123

    Thread Starter Member

    Dec 23, 2012
    36
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    i am using the Q going to the clock in both cases to drive the LED's because i want when every time someone enters or leave, the led is turned on..this is the only way to do so.
    how can i connect a volt regulator(5V) to my circuit so all the inputs are driven to 5v?(since i am using the main Vcc ground rail)
     
    Last edited: Dec 23, 2012
  16. MrChips

    Moderator

    Oct 2, 2009
    12,421
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    Remove LEDs from Q and put them on Q', source from Vcc.
    Pay attention to what people are telling you.
     
    Last edited: Dec 23, 2012
  17. Omar123

    Thread Starter Member

    Dec 23, 2012
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    Alright..i got it..but 2 more info's are missing..you still didn't tell me if every and every(including 7447,74283,7414)need a ceramic decoupling cap.. and if I need to keep the 10 microFarads on the schmitt trigger on their place or i don't need them and if the previous pic is the decoupling capacitor i can use
     
  18. Audioguru

    New Member

    Dec 20, 2007
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    You should look at the datasheet for the old SN7414. I do not know why your teacher did not provide it to you.
    The minimum input low voltage is 0.6V.
    The maximum input low current is 1.2mA.
    Then when the pushbutton is pressed, the 1k resistor connected to it produces a voltage of +1.2V at the input of the 7414 and IT WILL NEVER BE A LOGIC LOW.
    0.4V is a good logic low input voltage. A 330 ohm resistor will provide it.

    A TTL output has trouble making a valid logic high voltage when it powers an LED. Use an LED driver transistor or IC instead.

    YES, EACH old TTL logic IC needs to have its own 0.1uF ceramic decoupling capacitor plus one 10uF electrolytic capacitor for the entire circuit.

    Of course the Schmitt triggers need to have the 10uF input capacitors. The decoupling capacitors for the supply voltage are completely different.
     
  19. Audioguru

    New Member

    Dec 20, 2007
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    Deleted a duplicated reply.
     
  20. Omar123

    Thread Starter Member

    Dec 23, 2012
    36
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    yes i am using a 6v (4x1.5v battery) so do i need to replace the 1k with a 330 ohm? and at the end..can you please give me a reply for all the things i need to do since i am a little bit confused..btw the teacher didn't ask us to do this denouncing circuit of the jk counter, my curiosity played a role so i decided doing it.. the teacher didn't mention to us all this info since lab sessions (TTL) will be held next semester..and i am kind of new with logic circuits
     
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