Problem with 74192

Discussion in 'Homework Help' started by sigfred103, May 26, 2011.

  1. sigfred103

    Thread Starter New Member

    May 26, 2011
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    Someone please help me with this circuit I am creating. I have trouble in presetting the 74192 IC. I could present only the number 1, 2, and 3 but not the rest. presetting the IC with numbers 4 to 9 would display a zero on the 7-segment.
     
  2. Georacer

    Moderator

    Nov 25, 2009
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    Can you test if the 74193 output binary sequence is correct?

    If so, then the problem lies within the 7447 circuitry.
     
  3. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    Is that seen on both displays? That's odd.

    One thing to try is take a voltmeter and confirm the correct levels get to L1, L2, L3 and L4 on both chips. Then see if after a load the correct levels also appear on Q1 Q2 Q3 and Q3, then move on to the 74LS47's and see it is also correct at 1,2,4,and 8.

    I would be quite surprised if all of those levels are correct.

    How does it count? I bet it doesn't count just once per press of SW1 or SW2; you need some debouncing there.
     
  4. Georacer

    Moderator

    Nov 25, 2009
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    This is a good remark. If this is a real circuit, you will need an SR latch in all your switches. Now it is probable that the count will increase several time with each press.
     
  5. sigfred103

    Thread Starter New Member

    May 26, 2011
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    Thanks for all your help. I finally made it working. The problem was with the IC. and for the count up and down switches I used a 7408 AND with inputs A and B connected (1 AND 1 = 1). I also experimented with 7474 latch for debouncing the switches.
     
  6. Wendy

    Moderator

    Mar 24, 2008
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    You have another chip killer in that design. Resistors for LEDs are not optional. I'm am currently experimenting with a design that uses some odd characteristics of CMOS, but TTL uses bipolar transistors, which means if you try that for real the magic smoke will escape either from the chip or the LED, or both.
     
  7. sigfred103

    Thread Starter New Member

    May 26, 2011
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    Yeah, I forgot that one. I've placed a 330 resistors before the displays. Thanks for the reminder.
     
  8. SgtWookie

    Expert

    Jul 17, 2007
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    It looks like you are using 9v for the supply. That is much higher than allowed for 74LS TTL; the datasheet calls out a range of 4.5v to 5.5v for Vcc.

    Some 74C series go higher, but these are becoming fewer and further between. Many of the 74HC series are limited to 6v and less.
     
  9. sigfred103

    Thread Starter New Member

    May 26, 2011
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    I also forgot to change it in here. I'm using 5v power supply in my actual circuit. hehehe. sorry for the schematic.
     
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