7447 Troubleshoot

Discussion in 'General Electronics Chat' started by salabaal, Apr 25, 2010.

  1. salabaal

    Thread Starter New Member

    Apr 25, 2010
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    Hi,
    I have been working on a timer project with LED display.
    On friday, I got to see some numbers display on my dual 7-segment display. I must have made a few changes, but since yesterday, I can't seem to figure why my 7 segment display LED doesn't lit.
    I verified my connections, did some troubleshooting with the input to make sure that I was receiving signals in, but NOTHING COMES OUT THE OUTPUT, using the truth table.
    PLEASE HELP!
     
  2. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    Do you have a schematic?
    The photo is rather dark, can you make a clear picture of it?

    Bertus
     
  3. salabaal

    Thread Starter New Member

    Apr 25, 2010
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    Here is a better picture.
    I have a similar schematic in the same breaboard for a switch to resitor to 7447 to dual display 7 segment LED display, but neither works!
    My LED doesn't lit at the output, but I do have input signals on my input.
    Your help is greatly appreciated
     
  4. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    Where is the 7 segment display?
    Are legs of the resistors on the bottom not touching eachother?

    Bertus
     
  5. salabaal

    Thread Starter New Member

    Apr 25, 2010
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    Instead of jumping to a 7 segment display, I am using an LED to check my ouput.
    I have by passed this step because my 7 segment display wasn't lit.
    Below is the other diagram I have going for the switch to LED display, that too doesn't work.
    If I find the answer the problem 1 than I can save problem 2.
    Thanks for your time!
    Salab!
     
  6. salabaal

    Thread Starter New Member

    Apr 25, 2010
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    And by the way, all my connections are clear of each other. I did a double-check.
    Thanks Salab!
     
  7. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    Is the display common cathode or common anode?
    I see the display is connected to ground (if the blue line is ground).
    As far as I know the display should be common anode with resistors for each segment and the common connected to the plus 5 Volts.

    Bertus
     
  8. hgmjr

    Moderator

    Jan 28, 2005
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    The ground wire to your 74LS74's ground pin appears to connected to +5V.

    hgmjr
     
  9. bertus

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    Apr 5, 2008
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  10. salabaal

    Thread Starter New Member

    Apr 25, 2010
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    So again, where does the common anode connection goes?
    That's the only connection I don't have right now on the LED schematic.
    Second, what happened to the 7447 circuit I sent earlier, any idea why my LED doesn't come on.
    HGMJR, I fixed that, but my segment doesn't lit, so I am guessing that I need to do something with the common anode pin.
    Thanks
     
  11. salabaal

    Thread Starter New Member

    Apr 25, 2010
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    Bertus,
    I see that you answered the first question. Sorry for the misunderstanding.
     
  12. retched

    AAC Fanatic!

    Dec 5, 2009
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    Common anode goes to V+
     
  13. salabaal

    Thread Starter New Member

    Apr 25, 2010
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    I have done that:
    Connected LT (pin 3) to ground - > that is the only way I can get the LED the display
    RBI (Pin 5) and RBO (Pin 4) don't really care. They are at ground.
    I have a "C" displayed now. That's a good start, since I wasn't seeing anything at all.
    However, the "C" wouldn't change if I play with my switches.
    Does anyone know why?
    Thanks
    Sala
     
  14. hgmjr

    Moderator

    Jan 28, 2005
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    Do you have a circuit diagram that you can post? It is painful to try to figure out how the circuit is connected up just be looking at the photo.

    hgmjr
     
  15. salabaal

    Thread Starter New Member

    Apr 25, 2010
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    I agree but honestly,
    i have pictured the schematic in my head. I do not have one specific schematic to work from because there is none out there that utilizes my parts, at least that I could find, so I am using the datasheets from each component to make up the assembly. I wish I could hand sketch this circuit, but I don't have the tools either to scan it.
    I hope this will help:
    - 6 set of switches, but only using 4
    - Off end of switches all connected to +9V
    - ON end of switches connected to A, B, C and D of the SN74LS47N Chip
    - Pin of 7447 connected to ground and Pins 4 and 5 connected to +9V
    - Pin 16 of 7447 connected to +9V and Pin 8 connected to Ground
    - Pins 10 through 15 connected to dual display Seven Seg LED using 470 Ohm resistors
    - Pin 14 of seven segment connected to +9V and Pin 4 Connected to Ground

    Now that I think of it, is 9V too much to send to this circuit?
    Sala

    -
     
  16. retched

    AAC Fanatic!

    Dec 5, 2009
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    Yes. Yes it is.

    You have the data sheet linked in your last post. In it it says MAX 5.25v
    PAGE 9.
     
  17. salabaal

    Thread Starter New Member

    Apr 25, 2010
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    Thank you. Thank you!
    Your strategy helps identify the problem
    Now, I have a voltage regulator, does anyone know how I would use this with my 9V battery.
    Thanks again for your help.
    Salab!
     
  18. retched

    AAC Fanatic!

    Dec 5, 2009
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    Which regulator do you have?
     
  19. salabaal

    Thread Starter New Member

    Apr 25, 2010
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    I am using an NTE960,
    and I tried connected pin 1 of the regulator to the +9V of my battery,
    Pin 2 to the - negative terminal of my battery
    Pin 3 back to my circuit, and Pin the regulator to the negative terminal of my circuit.
    It still doesn't work!
    I am still getting the BIG RED "C" on my 7-segment display again!!!

    Salab
     
  20. salabaal

    Thread Starter New Member

    Apr 25, 2010
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    This should be a piece of cake.
    Why am I not there yet???
    Please help!
     
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