74192 Up/Down counter problems...

Discussion in 'The Projects Forum' started by JoeBro391, Jun 30, 2010.

  1. JoeBro391

    Thread Starter Member

    May 15, 2010
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    okay, so about a month ago i inquired on this forum about constructing a counter that could count both Up and Down in be displayed using a 7-segment LED display. I purchased a few 74192 counters and a few 4511 BCD decoders. My intent is to have the 74192 driven by a 555 timer in monostable mode, that can be switched between the Up and Down inputs (a switch between Ground and Pin 2 would send a pulse to to input of either the Up or Down input of the 74192). The 555 timer is CURRENTLY IN ASTABLE MODE however, until i get the circuit to work properly. The problem is, my circuit's not working :mad:

    I've constructed Up-counters, using 4026 before and it's a very easy build, however this one is proving much more difficult. It might have to do with the low-active components of the 74192 [opposed to high-active, which is when a high signal triggers the IC (though i'm sure most of you knew that)]. According to the datasheet for the 74192, the input that are not in use want to be kept high, while the few circuits i've seen keep them low). I've tried both arrangements, but to no avail.

    When I turn on the circuit (and yes, i'm using a regulated 5V for the enture breadboard) the 7-segment display I have shows "0" but does not change. Also, when i apply Ground to the 4511's Lamp Test (LT) pin, the 7-segment display reads "8" as it should. I know the 555timer works because i've tested it with LED's. It pulses at a rate of about 1000ms High-Low as per its configuration so I doubt that it's the problem. That only leaves the 74192 as the culprit (so basically, I probably have it wired incorrectly). It's current configuration goes as follows:

    1: +5V
    2: Pin 1 of 4511 (input B)
    3: Pin 7 of 4511 (input A)
    4: (UP INPUT) held high by 10k resistor (CURRENTLY CONNECTED TO PIN 3 OF 555 TIMER)
    5: (DOWN INPUT) held high by 10k resistor
    6: Pin 2 of 4511 (input C)
    7: Pin 6 of 4511 (input D)
    8: GND
    9: held high (5V)
    10: held high (5V)
    11: held high (5V) via 10k resistor
    12: (Carry) No Connection
    13: (Borrow) No Connection
    14: GND via 10k resistor
    15: held high (5V)
    16: +Vcc

    Perhaps i'm holding some high that should be low and/or vice-versa?

    Here's the datasheets for the 2 IC's

    74192 datasheet: http://pdf1.alldatasheet.com/datasheet-pdf/view/23048/STMICROELECTRONICS/74192.html

    4511 datasheet: http://pdf1.alldatasheet.com/datasheet-pdf/view/26905/TI/CD4511.html

    I currently don't posses and circuit-maker programs, but if somebody thinks that it'd be an easy way to fix this problem, (or at least, allow someone on this board to help me fix this problem), by all means, suggest a decent/free program and I'll get to work. Thanks. -Joe
     
  2. Wendy

    Moderator

    Mar 24, 2008
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    Hand sketch it and scan it, you don't need to be fancy, just legible.
     
  3. SgtWookie

    Expert

    Jul 17, 2007
    22,182
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    What is the part number on your 555 timer?

    If it's a BJT 555 timer, the output may not be going high enough to be detected as a logic "1". If it's a TLC555 CMOS timer, it might not have enough current source ability to clock the TTL ICs.

    [eta]
    Look at Bill Marsden's blogs; you can grab his "PaintCad" and use MSPaint to whip up a schematic.
     
  4. beenthere

    Retired Moderator

    Apr 20, 2004
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    You may have a major problem feeding a TTL signal to a CMOS IC. CMOS usually needs its inputs to go to Vcc, and TTL can't do that.

    Use a CD4510 for the up/down counter, and your problems may be over, after you figure out the different pinout.
     
  5. JoeBro391

    Thread Starter Member

    May 15, 2010
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    0
    Bill_Marsden: honestly, i'd love to have a circuit maker anyway, just because that way I could re-create other circuits i've made, to have on hand for reference. But in the meantime, i'll sketch this circuit, scan it and post it.

    SgtWookie: the 555 timer is a NE555N. As far as I know, it sinks/sources 200mA at (Vcc - 0.6V)

    beenthere: I've heard that before on other threads. Perhaps that is the problem. Maybe I could test out the funtionality of the 74192 with 4 LEDs and let it count in binary, the way it was specifically meant?

    thanks guys. -Joe
     
  6. beenthere

    Retired Moderator

    Apr 20, 2004
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    If you want to try just the '192, use 330 ohm resistors in series with the LED's to limit current.
     
  7. JoeBro391

    Thread Starter Member

    May 15, 2010
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    0
    here's the circuit as is:
    img018.jpg
    -Joe

    PS: for future reference, let me know of any decent/free circuit designer programs
     
  8. beenthere

    Retired Moderator

    Apr 20, 2004
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    Yep, that '192 can't provide a reliable input to the CD4511. If you want to try a kludge, add a 4.7K pullup resistor to the A, B, C, & D (pins 1, 7, 2, & 6 off the '192). That may boost the HIGH levels up enough to make the CMOS happy.
     
  9. JoeBro391

    Thread Starter Member

    May 15, 2010
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    Okay, I'm gonna try that. Do all the other pins look right? Is everything that should be held HIGH held HIGh and vice-versa?? Thanks. -Joe
     
  10. JoeBro391

    Thread Starter Member

    May 15, 2010
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    UPDATE: I got it working perfectly. In fact, i'll post a circuit diagram sometime tomorrow so no one else ever has these problems. Thanks for all the help everyone. -Joe
     
  11. JoeBro391

    Thread Starter Member

    May 15, 2010
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    Okay, I'm going to bed after messing around with this thing for a long time. It's 1:45am where I am. The circuit works fine, HOWEVER...there's a switch-bounce problem that i'm having. If I hook the Up or Down inputs the a SINGLE 555 timer, whether hooked up in astable or monostable mode, it works fine. If I take the connector between Pin 3 and the Input, the clock remains the same until replaced (Side Note: should I have the input connected to the 555 timer via a resistor or is it fine in a straight-through cable?). The Up works, the Down works; the problem is in the switching back and fourth. EX: counting up to 5, removing the connector from the Up input, connecting it to the Down input, and then resuming.

    First, in removing the cable, evenvwhen there's no pulse from the 555 timer, the digit on the 7-segment displays jumps a bit (i figure that's just regular bouncing). So I put a SPDT ON-ON switch into the circuit (the connector from PIN 3 of the 555 timer was the common and one pole connected to the Up input and the other to the Down input), but there was still some bouncing (even when there was no pulse from the 555 timer).

    Next course of action was to use 2 555 timers. At first I used a dual 556 timer (just got them in the mail today :D) but the results weren't working (i figured that i was either wiring them wrong or they were faulty), so I then used to separate 555 timers. They were working just fine (I tested them and had them in monostable mode). But when I hooked them up to the inputs (one to the Up and one to the Down), the display when all haywire, as though the button was just held low, and it just kept cycling through digits. But when i disconnected one 555 timer, and just used a SINGLE timer, the circuit went back to working just fine.

    Any ideas? thanks. -Joe
     
  12. JoeJester

    AAC Fanatic!

    Apr 26, 2005
    3,373
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    There are free simulation programs out there, circuit maker (Student), pSpice (Student), TINA-TI, and LTSpice.

    Go grab whichever one you want.
     
  13. beenthere

    Retired Moderator

    Apr 20, 2004
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  14. JoeBro391

    Thread Starter Member

    May 15, 2010
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    the logic simulator is a cool program (not that i can get it to work 100%), but not quite what i need. I'll try circuit maker (student)

    In the meantime, any idea what's causing the weird switch-bouncing, or whatever it is?? thanks. -Joe
     
  15. JoeBro391

    Thread Starter Member

    May 15, 2010
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    here's the current circuit. For this example, i'm using just a SPDT switch to toggle between the UP and DOWN inputs. In reality, I tried a SPDT switch, a 556 dual timer, and 2 555 timers and nothing worked. The only think that worked was manually switching the output cable from the UP input to the DOWN input, and there was still some switch-bouncing.

    ...okay, the file is apparently invalid and won't upload. I used Circuit Maker (student) and it is a CKT file. Any reccomendations?? -Joe
     
  16. SgtWookie

    Expert

    Jul 17, 2007
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    Download LTSpice from Linear Technologies. Google "LTSpice Download" to get there.

    Join the LTSpice User Group on Yahoo! Groups. Lots of models and help there.

    CircuitMaker Student might be found out there, but it's a dead-end product, and won't run on Vista, and probably not on Windows 7.

    Cadsoft Eagle is available in a freeware mode. Pretty powerful, but you're limited to a 3"x4" board and just 2 layers - still, plenty for a lot of hobby projects.
    cadsoftusa.com is the site

    Sparkfun has an Eagle tutorial; go through it to save yourself a struggle.
     
  17. JoeBro391

    Thread Starter Member

    May 15, 2010
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    oi, i really don't like the LTspice program. CircuitMaker was so much more straight-forward; and I can't even figure out how to insert a simple switch on LTspice...:confused: guess i'll just draw up a new one and scan it like yesterday. -Joe
     
  18. eblc1388

    Senior Member

    Nov 28, 2008
    1,542
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    I've noticed that you have connected 10K resistor on TTL input pins to trying to pull the logic level down to low.

    This might seem to work but the value is way too high for TTL.

    Either connect the pin directly to ground or use a resistor with value less than 100Ω if you have to.

    There is no problem with pulling a pin high using 10K but usually the pin is just connected to +5V in various design.
     
  19. JoeBro391

    Thread Starter Member

    May 15, 2010
    68
    0
    which pins are you referring to? if it's the Up/Down inputs on the 47192, those are being kept HIGH. what problems do you think too high of a resistor value would lead to? thanks. -Joe

    Here's the current circuit. This circuit works just fine, for the exception of switching back and fourth between the Up and Down inputs.
    74192 counter A.jpg
     
  20. eblc1388

    Senior Member

    Nov 28, 2008
    1,542
    102
    It is the first schematic drawing I'm referring to. I see that you have since corrected this in the current drawing.

    A 10KΩ pulldown will not work reliably(or work at all) in case of TTL input which expects direct connection to 0V or to the output of a logic gate.

    [​IMG]
     
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