555 counter and 7 seg display won't work

Discussion in 'The Projects Forum' started by Adv.Logic, Dec 28, 2010.

  1. Adv.Logic

    Thread Starter New Member

    Dec 4, 2010
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    We have a project that counts 0-9 using a 555 counter and display it using a 7segment but when I combined the counter and for the display, not all the number will display.Only the 0, 4 and 5 will out. I tried them in the proteus and it works. In the picture that I attached below, I connect the output of the counter with the input for the display.
     
  2. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    What singnals are there on the LT,RBI,BI pins?

    Take a look in the datasheet what is needed over there.

    I also see no current limiting resistors for EACH segment of the display.
    A 470 Ohms resistor at each segment will do.

    Bertus
     
  3. Wendy

    Moderator

    Mar 24, 2008
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    Without current limiting resistors you may have burned up one or both of the components. When dealing with LEDs resistors are required, always.

    Unused logic inputs (never outputs) MUST be given a logic one or zero, depending on the chips. Again, this is required, not an option. It usually won't smoke anything, just cause abnormal operation.
     
  4. Adv.Logic

    Thread Starter New Member

    Dec 4, 2010
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    I only put 1k resistor on the vcc of the 7segment and their LEDs, I directly connect them to the decoder. And the LT, RBI and BI are in high.
     
  5. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    When you put only one resistor in the +Vcc line of the display, the display will work, but the more segments are illiminated the more dimm they will be.
    Use a resistor with each segment to have all segments illuminated equal.

    BTW what do you mean with nor working?
    What is on the display or not?

    Bertus
     
  6. k7elp60

    Senior Member

    Nov 4, 2008
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    I agree with bertus and Bill. I can add that you also need a capacitor(10uf should do)between pins 4,8 and pin 1 of the 555 timer. The voltage for the circuit should be very close to 5V and the 100K pot near maximum resistance for approximately 7Hz clock.
     
  7. Adv.Logic

    Thread Starter New Member

    Dec 4, 2010
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    I have a question about the potentiometer in the counter. Is it necessary to fix the value of the pot? Because I think pot only controls the speed of the counter and you can turn it what you want to?
     
  8. Wendy

    Moderator

    Mar 24, 2008
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    Yes, the pot can be replace with a simple resistor. I usually put pots in my designs because I don't know what the ideal speed is, but if you do know what you want it is highly predictable (and the equation is very simple).
     
  9. Adv.Logic

    Thread Starter New Member

    Dec 4, 2010
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    So, it doesn't effect my circuit? Because I thought the pot should in specific resistance to run the display to 0-9? Because when I test run the circuit, sometimes it only displayed 1 to 6 only and when I test it again it will displayed 0-1-2-4-6-8 and there are also it runs correctly from 0-9 but afterwards when I disconnected it from the source and try it again, it will go back to the abnormal display.
     
  10. Wendy

    Moderator

    Mar 24, 2008
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    Do you still have a 1KΩ resistor on Vcc? This is an illegal setup if it is. The chip should have a direct connection to the power source, with a bypass capacitor on the power pins, to give the logic the power it needs to run correctly. The resistors to limit the current should be one resistor per LED (for a total of 7).

    Did you look at the link I showed?
     
  11. Adv.Logic

    Thread Starter New Member

    Dec 4, 2010
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    I already tried that one also. I put a resistor in each led with a 220 resistant. But still the same with only one resistor on the vcc.
     
  12. Wendy

    Moderator

    Mar 24, 2008
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    I said it before, but there should be NO resistor going to Vcc. The power supply pins go directly to the power supply. Each output to a segment on the display should have a resistor.

    This is pretty much spelled out in the data sheet.

    7447 datasheet

    [​IMG]

    Just curious, have you studied open collector logic yet?
     
    Last edited: Dec 31, 2010
  13. JoeJester

    AAC Fanatic!

    Apr 26, 2005
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    Since you are insistent on using the design you specified in the original posting, attached is a problem for you to consider ....

    Once you correct that output problem, what have you done with the RBI, Blanking, and Lamp Test pins?

    With those two deficiencies addressed, your seven segments will work. You can test that by applying the appropriate logic level to A-B-C-D input of the 7447 and increment the seven-segment display through all numbers, 0 - 9.

    What test equipment do you have available?
     
    Last edited: Jan 4, 2011
  14. Wendy

    Moderator

    Mar 24, 2008
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    The OP is going to need a common anode LED indicator, or use the open collector inputs to drive transistors with can drive common cathode display unit instead. This is why I was asking about whether he had studied open collector.

    Thing that surprised me is how similar the 4511 and the 7447 are to each other. They are very close (but not quite) to being drop in replacements for each other, only one pin is different. I came across this little fact when I was drawing the schematic I posted 2 posts ago.
     
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