Digital Clock Help

Discussion in 'The Projects Forum' started by RussellJ, Nov 15, 2013.

  1. RussellJ

    Thread Starter New Member

    Nov 13, 2013
    4
    0
    I am working on a project to build a digital clock. I'm doing something wrong because its not even powering up. I'm sure it's something stupid but I can't figure it out. Is my voltage too low?

    And if I were to do it how would I convert this to a 12 hour clock? Only program I know and can use is multisim.

    Any help at all is most appreciated. I am coming up short searching the internet.
     
  2. Papabravo

    Expert

    Feb 24, 2006
    10,135
    1,786
    It is common for schematic symbols to exclude the Vcc and GND pins as "unnecessary detail". It is presumed that you will connect the Vcc and GND pins along with some decoupling caps for each of the TTL packages in your design without having to show them on the schematic.
     
  3. RussellJ

    Thread Starter New Member

    Nov 13, 2013
    4
    0
    So I have to do something with the Digital Vcc and Grnd? Im not familiar with the Vcc and Digital ground but they were called for in the circuit based off instructions.
     
  4. Papabravo

    Expert

    Feb 24, 2006
    10,135
    1,786
    Yes. In schematic capture packages associated with PCB layout software this is normally handled automatically in the layout phase. I can't read the symbols in the screenshot you provided, but I don't see any explicit connections to the Vcc and GND pins of the IC's which according to my recollection should be on the opposing corners of the DIP package. For a 16-pin DIP, GND should be pin 8 and Vcc should be Pin 16. This is the general rule, but you have to double check with the datasheet in ALL CASES.

    One more thing. I do not see ANY decoupling capacitors on your schematic. Your project is unlikely to work without them. Before you ask me about them try this link:

    http://lmgtfy.com/?q=Decoupling+Capacitors
     
  5. RussellJ

    Thread Starter New Member

    Nov 13, 2013
    4
    0
    It says those connections are hidden virtual connections when I placed the Vcc. When I placed the Vcc it says those connections were made. Is there a way for me to do it manually in multisim?
     
  6. RussellJ

    Thread Starter New Member

    Nov 13, 2013
    4
    0
    Here is my multisim file if that helps.

    Edit, would not let me upload the multisim file. had to zip it.
     
  7. Papabravo

    Expert

    Feb 24, 2006
    10,135
    1,786
    I could have saved you the trouble since I cannot open a multisim file. Regardless of how multisim handles Vcc and GND you have to make actual connections in the real world. Do your chips have anything on the corner pins?
     
  8. tshuck

    Well-Known Member

    Oct 18, 2012
    3,531
    675
    Wait, are you trying to simulate the clock, or build a real one?

    The simulation works then?

    If you are building it, post a picture of your setup.
     
  9. Liaquat Ali

    New Member

    Oct 19, 2012
    2
    0
    dear Russellj use common anode 7 segment display and break connection of 10 and 15 pin of 7447N from Hour side and also break the connection of D & F of 7 segment (U18) join D with 10 and F with 15 of 7447N (U11) ic of Hour side..
    if u have any confusion, read carefully
    regards
    Liaquat Ali
     
  10. WBahn

    Moderator

    Mar 31, 2012
    17,715
    4,788
    You have one 7SEG display with its common pin tied to Vcc, but it appears all of the other 7SEG common pins are tied together and driven by two segment outputs in the hours section that are tied together as well. Are you sure that's what you want?
     
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