questions about 74193 counter

Discussion in 'The Projects Forum' started by gcentauri, Jan 25, 2009.

  1. gcentauri

    Thread Starter New Member

    Jan 25, 2009
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    hi, I'm a fairly new hobbyist, and i've been trying to teach myself some things about TTY circuits. I had a set of TTY chips laying around and decided that I'd see if I could make them 'do' something. So my first project has been to try and make a 7-segment display count up from 0 to 9 using some kind of button press.

    The counter chip I had on hand was a 74193, and I've spend a lot of time reading up on it and trying to make it work, but for the life of me I can't get the thing to count. I've tried many different set-ups but haven't had any luck. I'm wondering if I'm not sending it a pulse that it can recognize as a clock cycle, or if there's just something weird with the chip. Right now I have a 7400 chip debouncing a switch and and output from that going into the count-up terminal of the 74193. The count-down terminal is held high. When I flip the switch I know I'm getting a slow pulse (maybe that's the problem, and if so, is there a circuit I can build to make a quick single pulse?) but nothing is happening at any of the output terminals. They all just stay at low, even though I'm giving the counter input a pulse.

    I hope I've described my situation well enough, I just can not figure out why the counter isn't counting. My best guess is that the pulse is too slow, but even when I apply a 200 Hz square wave nothing happens. Any help would be great. I have read the data-sheets and read quite a bit on this forum as well, but nothing I try seems to work. Thanks.
     
  2. Wendy

    Moderator

    Mar 24, 2008
    20,764
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    I suspect you mean TTL chips (Transistor Transistor Logic). We'll need the schematic you're useing to help.
     
  3. SgtWookie

    Expert

    Jul 17, 2007
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    Do you have LOAD (pin 11) held high? If not, it'll always be loading the data inputs into the data outputs.
     
  4. hgmjr

    Moderator

    Jan 28, 2005
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    214
    Also MR (Master Reset pin 14) must be LOW or the counter will be stuck in the output cleared state. Confirm that 5V power is present on the Power pin (pin 16) and ground is present on pin 8.

    hgmjr
     
  5. italo

    New Member

    Nov 20, 2005
    205
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    This IC is a discontinue item. but pin 14 must be low to count, pin 11 must be hi to count, and what are you loading the register with 12 count up 12 count down? you must load it with something low and stay hi to count.
     
  6. gcentauri

    Thread Starter New Member

    Jan 25, 2009
    3
    0
    hey thanks everyone. yes I meant TTL chips, I'm not sure why I typed TTY.

    I followed your advice and held pin 11 (load pin) low and held pin 14 (reset) high and the counter counted! it still behaves a bit strange, it counts up to seven and then resets to 2 and counts up to 7 again. but i'll count this as a success! i am a bit confused about how one would know to hold those pins high and low, the data sheet didn't really convey that.

    as far as posting schematics go (since i'm new to the forum) would one just create a schematic in a circuit layout program? i'm using linux, and haven't really used any of the electronics software available yet, but i'm definitely interested. if anyone has any tips, suggestions, or resources it would be appreciated. thanks alot.

    grant
     
  7. hgmjr

    Moderator

    Jan 28, 2005
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    The information is contained in the truth-table in the datasheet. Often there is a timing diagram that contains the same information along with the critical timing information as well.

    hgmjr
     
  8. gcentauri

    Thread Starter New Member

    Jan 25, 2009
    3
    0
    i did notice the timing diagram, but was having a bit of trouble deciphering it. This was my first experiment with digital logic though, so maybe it will just make more sense as I work with things. again, i appreciate the help.
     
  9. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    Load must be high and Reset must be low in order to count. I suspect you meant to say that that's what you did.
     
  10. SgtWookie

    Expert

    Jul 17, 2007
    22,182
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    Double-check your connections. It sounds like you may have accidentally connected pin 1 (Data B in) to 16 (Vcc), and pin 7 (Qd) to pin 11 (LOAD).

    Which datasheet were you looking at?
    Texas Instruments' datasheets are pretty good for TTL.

    You might wish to have a look here:
    http://www.geda.seul.org/docs/20040111/spice-sdb/simulation.html

    I'm running LTSpice on Windows 98 Pro; the fellow who wrote that page is running it under Linux; apparently everything works except for the help system.
     
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