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Counter using 74LS90 and 74LS47

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by MattAyers, Mar 20, 2004.

  1. MattAyers

    MattAyers New Member

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    Hi,

    I've been trying to build this circuit:

    [​IMG]

    I have all the components in a breadboard and have even modelled it on multisim 6.02 and 7, but can't get it to do anything!

    Has anyone else tried this circuit, or made a counter from these ic's?

    Any help / response would be appreciated!

    Matt.

    Reference:
    http://www.aaroncake.net/circuits/counter.htm

    Seaches tags: 7490 7447
     
  2. Russlk

    Russlk New Member

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    Your 74ls90 is OK, but on the 74ls47, pins 3, 4, 5 should be tied high.
     
  3. MattAyers

    MattAyers New Member

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    I've tried that, I've just modelled this circuit:

    [​IMG]

    As you can see the 74LS90 is working just fine, but no matter what I do to the 74LS47 it doesn't display anything!

    The outputs are always high. Even tried fixing the inputs to low and checking the IC's truth table. Still I get all the outputs as high.

    Anyone got anymore ideas?

    BTW: I know the signal source voltage component has a stupidly high count frequence but it runs fine with the generated time step.
     
  4. dave

    Dave New Member

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  5. samcheetah

    samcheetah New Member

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    no Russlk there is no need to do that. if the pins 3, 4, 5 are left open it means it is high. so there is no need to tie it to high. and certainly that cant be the problem here.

    MattAyers i built a project in which i used a 74147 before the 7447 and then a 7 seg and i had the same problem in multisim. u can search the post i made a few days ago. my display didnt show anything. but then i physicall built the circuit on a breadboard and it worked fine. i think there is something missing that i and u dont know. i hope someone clears this confusion
     
  6. Sebi

    Sebi New Member

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    Samcheetah, the logic inputs always need H or L level. Never left open.The floating input many times work as H, but very sensitive for disturbances.
     
  7. panic mode

    panic mode Well-Known Member

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    the circuit looks ok except for the way too high values for LED
    current limiting resistors. I would put 220 or 330 instead of 4k7.
     
  8. samcheetah

    samcheetah New Member

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    sebi it wasnt my opinion but i read that thing from the data sheet of the 7447 IC. if u download the data sheet of the IC, read the notes written in a small font. for pin 3, 4, 5 it says either leave it open or make it high.

    mattAyers have u got any luck with the circuit?????????
     
  9. MattAyers

    MattAyers New Member

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    Status update

    Hi, I haven't made much progress on Multisim but have the circuit laid out on a pcb which kind of works but seems quite random!

    But I think the randomness could be down to my old power supply that barely gives out enough current to power one ic let alone the pair!

    At the moment the 7 segment display only displays an 8 or 0, or possibly a 9 if I’m lucky. To count with the circuit I'm simply connecting pin 14 of the ic 74ls90 to -ve which isn't the best of methods so could be that.

    One thing I find quite strange is that everything seems to be connected to everything else, well almost - if I do a continuity test. I'm not very experienced with electronics, so would be great to hear any reasons as to where I might be going wrong.

    Here's a pic of my current project:

    [​IMG]
     
  10. Sebi

    Sebi New Member

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    For proper work You need proper signal source. When You make a contact with wire or pushbutton, it is many pulses for counter input.
    Use a simply debouncing cct.
     
  11. carlosthejackle2001

    carlosthejackle2001 New Member

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    we had built a similar circuit, the problem being was the switch, it needed to be a good debounced switch then the count worked fine, multi sim seemed to be a bit random sometimes worked sometimes didn't although seems to work better with virtual components in more complex circuits
     
  12. MattAyers

    MattAyers New Member

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    Update

    I got the circuit working, the problem why it was only displaying a 9 and a 0 was because 2 of the output leads were connecting underneath where i could see.

    Must have been the outputs Q0 and Q3 to give the 7 segment display driver the value of 9!

    Still haven't had any success on electronics workbench - something funny there!

    If anyone needs information on the circuit or just general hints and tips feel free to contact me, I'm thinking of setting up a simple electronics website when I have the time out of college.

    Oh this is off topic but does anyone know where / how to download / install new or extra components for electronics workbench 7?
    It's not really for my benefit, just my friend has a decade counters / 7 segment driver IC all in one, but it skips right past it so he has to draw it by hand.
    I believe his IC is 47ls193 but I could be wrong.

    If I don't get any response here I may make a new post so if you think you're seeing double you probably are.

    Thanks for all of your help!
    Matt Ayers.
     
  13. Digimaniac

    Digimaniac New Member

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    The Same Design but different purpose

    Hey Guys,
    I made the same design of this circuit but for the purpose to use it as a digital clock so the first part of the seconds consists of the your design exactly , first the pins of the 74ls47 , 3, 4 and 5 can left open or joined to the VCC it doesn't make sense and I experimented both ideas, but I had another Idea if you can help me it will make me more thankful.
    PLease I wanna make the 74ls90 work as a Decade 6 Counter(0-5) if you got any idea about this please inform me.
    Yours Aly
     
  14. MattAyers

    MattAyers New Member

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    Hi Digimaniac,

    I have a feeling, reading through the 47ls90 pdf file that you can use the ic 47ls92 as a 0-6 decade counter, and it may be easier to use that. But the other way that comes to mind is resetting the chip when the count reaches 6, eg: When the bits:
    Q0 Q1 Q2 Q3 Decimal
    0 1 1 0 6
    Just use an AND gate and set its output to the 47ls90's reset pins: MR1 (pin 2) and MR2 (pin 3)

    Hope that helps!
     
  15. carlosthejackle2001

    carlosthejackle2001 New Member

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    The circuit that you have been trying to build worked fine on the old electronics workbench but doesn't seem to work on the new one! I would try and build the circuit practicaly and see how it goes
     
  16. ljcox

    ljcox Well-Known Member

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    Your circuit does not appear to have any bypass capacitors.

    These are essential in order to avoid odd behaviour due to coupling via the supply line. A 100 nF ceramic is sufficient across every second IC.

    Also, you mean a Modulo 6 counter, not a "Decade 6". A decade counter is a Modulo 10.

    I posted a Modulo 6 counter last week, it was CMOS, but the same principle can be used with TTL.

    Len
     
  17. tresca

    tresca Member

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    understanding the logic behind a 74ls90

    My problem is related to these components. I'm trying to understand how I can set my own sequence of numbers with a 74ls90(decade counter) and 74ls47(BCD to seven segment decoder). I've manged to understand to understand to figure out how to reset a count if the numbers are consecutive(0.1.2.3..0..etc..), but I'm having trouble trying to set 0,3,4,7,0 or 0,2,4,6,0.

    I'm been playing with it for sometime and tried the net but couldnt find anything specific. If somebody knows and if they could explain it to me, that would be great.

    Thanks
     
  18. Barry

    Barry New Member

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    Hi all,
    I found a good schematic for a four decade counter using 4026 IC's with a switch debouncing circuit as well. It does not use the same IC's as in this discussion but you can add as many seven segment displays as you want.
    The 4026 IC only drives common cathode seven segment displays and the nice part here is that only one IC per display necessary.
    If you are interested the project is at :

    http://braincambre500.freeservers.com/decade counter.htm

    Barry.
     
  19. ljcox

    ljcox Well-Known Member

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    Re: understanding the logic behind a 74ls90

    The only way I can see to do this is to configure the counter as a Modulo 4 and then design gating to give you 0, 3, 4, 7 rather than 0, 1, 2, 3. In other words, the counter is actually counting 0, 1, 2, 3, but the gating converts these to 0, 3, 4, 7 which then drives the binary to 7 segment IC.

    To obtain 0, 2, 4, 6 you would use a diffiernt gating design.

    Len
     
  20. Mr Replay

    Mr Replay New Member

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    Greeting to all.

    I built that circuit in electronics worbench and it acts like crazy.the problem is not the circuit , for some reason the 7 segment display that should turn ligths on at high input ( as explained in help option :roll: )is inverted so it ligths in low level.
     
  21. k7elp60

    k7elp60 Active Member

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    Digimaniac,
    If you tie pin 8 to pin 2 and pin 9 to pin3 of the 74LS90 it will reset to zero on the 6th count. Pins 2 and 3 are a 2 input nand gate. On the 6th count Qb and Qc are both high. The internal NAND gate on pins 2 and 3 will
    go to 0 and reset the counter.

    On a simiar subject pins 6 and 7 are a NAND gate that will reset the counter to 9
     

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