Some help with 7 Seg LED disaplay

Discussion in 'Homework Help' started by tupadjia, May 10, 2010.

  1. tupadjia

    Thread Starter New Member

    Apr 25, 2010
    6
    0
    I have a little project that includes a 7 segment led display. using only 2 SPDT switches, i have to wire this thing using only NAND or NOR gates numbers 0-3. when all switches are down, the display would show 0.
    Switches are B0 and B1. LED config goes: A,B,C,D,E,F and G. Since the segment display needs a resistor before each led, on my truth table i need to invert all leds that are on to a 0.

    so,

    B0 | B1 | o/p
    -------------
    0 0 0
    0 1 1
    1 0 2
    1 1 3

    and,

    B0 B1 A B C D E F G
    0 0 0 0 0 0 0 0 1
    0 1 1 0 0 1 1 1 1
    1 0 0 0 1 0 0 1 0
    1 1 0 0 0 0 1 1 0

    Now that I have the truth tables up and ready to go, how do i go about designing a schematic using either a nand or nor IC to make this work?
    I want to thank anyone for attempting to help me out. thank you so much in advance!
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    (quoting) so,

    Code ( (Unknown Language)):
    1. B0 | B1 | o/p      
    2. -------------
    3.  0    0    0
    4.  0    1    1
    5.  1    0    2
    6.  1    1    3
    7.  
    8. and,
    9.  
    10. B0  B1  A  B  C  D  E  F  G  
    11.  0   0  0  0  0  0  0  0  1
    12.  0   1  1  0  0  1  1  1  1
    13.  1   0  0  0  1  0  0  1  0
    14.  1   1  0  0  0  0  1  1  0
    (/quote)

    I've added (code) and (/code) tags so that your tables have their intended formatting.

    This certainly looks like a homework assignment given to you by an instructor/professor/teacher. Is it?
     
  3. tupadjia

    Thread Starter New Member

    Apr 25, 2010
    6
    0
    Yes, thank you for doing that. After I posted I noticed it got all screwed up. But yes, it was assigned by the instructor. My problem is that I don't know in which direction to go once I have the truth tables. apparently there are a few ways, but each way i get stuck.
     
  4. tupadjia

    Thread Starter New Member

    Apr 25, 2010
    6
    0
    Again, I don' want someone to do it for me, I just need the direction I should be going in ie, explain to me what needs to be done.
     
  5. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Well, start by doing some research.

    Search for "NAND gate" and "NOR gate" using Google. Wikipedia has some good entries on those gates.

    Then look at a datasheet for a SN7447 IC. That's a 7-segment LED driver for TTL.
     
  6. tupadjia

    Thread Starter New Member

    Apr 25, 2010
    6
    0
    ok, so i got my breadboard ready, and using 74hc08 (and gates), i got so far that its 90% correct, the proper leds turn on and the whole nine yards but a couple didn't, i believe inversion problem was the case. however, i used the truth table to find out the equations. i didnt use kmaps. where do you think i went wrong when getting the equations from the truth table?
     
  7. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    I think you went wrong when you wired up those few that don't light - or you didn't bother to use current limiting resistors, and fried either the LEDs or your NAND gates.

    But post your schematic.
     
  8. tupadjia

    Thread Starter New Member

    Apr 25, 2010
    6
    0
    I didn't burn anything as the leds still work and i did use resistor for current limiting. i think the problem might have been in the wiring seems how i wired everything so fast. i will post the schematic later as it is reaching midnight.
     
  9. bertus

    Administrator

    Apr 5, 2008
    15,649
    2,348
    Hello,

    I moved your thread to the "homework help" section.

    If you want to read more on decoders, take a look at the links of this page:
    http://www.educypedia.be/electronics/digitalcodes.htm

    There are more pages like that over there on other digital subjects too:

    Digital electronics:
    Arithmetic circuits D/A-A/D converters Number systems Codes and decoders Flip flops Technology Counters and registers General overview Technology-CMOS Digital logic Memories Technology-TTL Timers and oscillators

    Greetings,
    Bertus
     
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