[How To] Connections for a 74192 decade counter to a (7448 or 7447) BCD to 7 segment :(

Discussion in 'Homework Help' started by nubpwn3r, Oct 23, 2015.

  1. nubpwn3r

    Thread Starter New Member

    Oct 15, 2015
    15
    0
    Im working on a traffic light simulation, and we are suddenly tasked to add a 7 segment.
    We used a 74192 decade counter and I am finding it hard to find the necesary connections for the 74192 to a 7448 or 7447 7 segment decoder.

    halp pls im toasted
     
  2. GS3

    Senior Member

    Sep 21, 2007
    408
    35
    I don't understand. You got four bits. You connect A to A, B to B, C to C and D to D. Where is the confusion?
     
  3. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,969
    744
    The outputs of the 74192 are labelled Qa,Qb, Qc, Qd, just connect them to inputs A,B,C,D, OR 1,2,4,8, on the decoder driver,

    where is the difficulty?
     
  4. nubpwn3r

    Thread Starter New Member

    Oct 15, 2015
    15
    0
    ive tried that, connecting QA - QD to input A - D
    the output is just a steady HI State
    hence when connected to the 7 segment, all LED are on (8)
     
  5. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,969
    744
    Which decoder is it,whats the voltage state of the inputs to the decoder, high or low, and how have you connected the Lamp test pin?
     
  6. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
    2,793
    829
    First, do you have a schematic?

    One possibility, how is pin 3 on the 7447 wired?

    Second, can you check the outputs of the 74192? ABCD should be 1000b. If all the outputs (Qa, Qb, Qc, & Qd) are high, none of the segments should be lit. Here is the datasheet for the 7447/7448

    How are the data lines wired on the 74192 (those marked ABCD)? What is the LOAD pin connected to...

    Finally, do you have a schematic?
     
  7. nubpwn3r

    Thread Starter New Member

    Oct 15, 2015
    15
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    Here is my schematic at the moment (courtesy: docircuits.com), it counts down from 9 to 0
    Schematic.PNG
     
  8. eetech00

    Active Member

    Jun 8, 2013
    646
    110
    Hi

    Here is a connect diagram for connecting a 74192 with a 7447.
    The AM1 thru AM7 are measurement points for the sim. There will
    really just be straight wires between the resistor pack and 7447.
     
  9. nubpwn3r

    Thread Starter New Member

    Oct 15, 2015
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    ahhh foolish me only thing i did wrong(?) is not connecting pin 4 of the 7447 to the supply because as much as possible, unused pins (dont care) should be connected to logic HI state according to my professor
     
  10. eetech00

    Active Member

    Jun 8, 2013
    646
    110
    Hi

    Well...not exactly. An unused input pin should be connected so that it's function is in its inactive logic state.
    For example, on the 7447, The "LT" pin requires a low logic level to activate the Lamp Test function, so I connected to a high logic level (VDD). But the "CLR" (reset) function on the 74192 requires a high logic level to activate the CLR function, so I connected it to a low logic level(GND).
     
    Last edited: Oct 25, 2015
  11. nubpwn3r

    Thread Starter New Member

    Oct 15, 2015
    15
    0
    mhhm i got it figured after browsing on my notes thanks you all. thumbs up. +++1
    I really appreciate the help.!!
     
  12. dl324

    Distinguished Member

    Mar 30, 2015
    3,214
    619
    There are exceptions to this "rule". For example, CMOS gates dissipate very little power when not switching, so tying unused inputs HI or LO is a matter of convenience.

    It would be more correct to say that unused inputs should not be allowed to float.
     
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