help!!

Discussion in 'Homework Help' started by keithisdoped, Aug 22, 2011.

  1. keithisdoped

    Thread Starter New Member

    Aug 22, 2011
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    0
    i designed a two digit up counter using 2 x 4511 and 2 x 74192.
    my schematics are as followed, in multisim it is fully functionally working but when i build it out there is a problem, the number do not increase in sequence but rather jump all about, i found the problem which is the 74192 but i do not really know why. it does not output as expected ( 0000 , 0001 , 0010 , 0011 )
    but rather in the same sequence as what i'm seeing on the led.. i would be delighted if some one can tell me the flaw in my design or the reason why my counter is acting like this! and yes my Vcc and Vdd are connected except my inputs A-D.

    this is urgent D: i have been dwelling on it for 4 days please help! and sorry if the answer is just in front of me because it's only my first year in electrical engineering. all helpful comments that will help better my understanding would be appreciated!
     
    Last edited: Aug 22, 2011
  2. MrChips

    Moderator

    Oct 2, 2009
    12,452
    3,371
    Try to post a more descriptive title, duh.
    We are geniuses, not mind readers.
     
    Sparky49 likes this.
  3. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    7,395
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    Is S1 your count UP button?

    It needs to be debounced least it give any arbitrary number of pulses every time you press it.
     
  4. elec_mech

    Senior Member

    Nov 12, 2008
    1,513
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    Hi keithisdoped,

    I have to agree with MrChips, you need to change your title - generally everyone who posts something here wants help or input, that's a given. The title needs to reflect what it is you need help with, in this case a two digit 7-segment display circuit. This helps you because people with a backgorund or interest in your problem will want to help out. Most people won't bother to read posts with titles like "Help", "Urgent", etc.

    That said, in looking at your circuit, there are a few things that need addressing.

    1) As I recently learned myself, you need to put a 0.1uF capacitor (ceramic or poly are fine) between Vcc and GND for EVERY IC. This helps take out noise.

    2) Put a pulldown resistor, say 10kΩ, on CLR on both 74192Ns. When the S2 is not pushed, CLR is floating. You want it to stay low when S2 is not pressed.

    3) Put a pullup resistor, again 10kΩ, on the UP input where S1 is connected. Same reasoning, when S1 isn't pushed, UP is floating which can wreck havoc.

    4) Use a switch debouncer between S1 and S2 and the 74192N inputs. You can do this with a simple resistor and capacitor or use a 555 or a CD4093 in a comparator mode. If you need help with this, let us know.

    5) Tie pin 5 on both CD4511 to ground.

    6) Tie pins 1, 9, 10, & 15 to ground on both 74192Ns. This shouldn't hurt anything, but it never hurts to tie inputs, used or not, to either Vcc or GND.

    7) Make sure there is an electrolytic, say 220uF, and a ceramic capacitor, say 0.1uF, between the + and - terminals of your power supply to help remove any ripples or noise. Make sure they are rated at least 10VDC or higher. 16VDC or higher would be ideal.

    One or more of these things is allowing noise into your circuit which is causing it to act funny - number 4 is the biggest culprit. All of these need to be addressed because they can all cause your circuit to run amock.

    Good luck!
     
  5. MrChips

    Moderator

    Oct 2, 2009
    12,452
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    Shucks, I would have waited for the op to respond.

    Anyway, here is a proper title: 74192 Counters display erratic counts.

    The problem is switch S1 needs to be debounced. Here are two simple ways to do that:

    [​IMG]


    or use a slow 555 timer to clock the counters.

    Also as elec_mech pointed out, CLR on pin-14 must be pulled down. I would use 220-ohm resistor to GND.
     
  6. elec_mech

    Senior Member

    Nov 12, 2008
    1,513
    193
    MrChips,

    As he's using 6VDC for a supply, will the 7400 series be okay? In doing a quick lookup, they recommend a max of about 5.25V, although they claim to accept up to 7V absolute max.

    If not, a CD4011 will work in place of the 7400 and a CD40106 will work for a 74LS14.

    Personally I like the look of the 74LS14/CD40106 debouncer circuit, few parts and wiring.

    Sorry, this looked fun to me and a gave me a chance to apply some problem-solving skills, many of which were recently acquired here.
     
  7. MrChips

    Moderator

    Oct 2, 2009
    12,452
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    I hadn't noticed the 6V power supply. No, power supply should be 5V for 7400 series.
    Yes, it is ok to replace 74LS00 and 74LS14 with 4000 series. (Resistance values will have to be changed. 10K ohms would be ok).
    But I don't think the 74192 should be run at 6V.
     
  8. elec_mech

    Senior Member

    Nov 12, 2008
    1,513
    193
    MrChips,

    You are right, I glanced at the datasheet but just read closer - the 74192N is also only rated for a max of 5.25V.

    keithisdoped,

    I'd suggest switching the 74192N with a CD4510. You'll have to tie the up/down pin to Vcc to keep it counting up and put S1 on the clock input. Alternately, if you can change the voltage to 5V using a 7805 or similar, you can stick with the 74192N.
     
  9. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    If you are going to mix 74 series and 4000 series ICs, you will need to use level translators. You can't just connect them up and expect them to work properly.
     
  10. keithisdoped

    Thread Starter New Member

    Aug 22, 2011
    14
    0
    ahhh as i found out today the problem in the switch.. which the de-bouncing method (both are very clear to me) helped !
    As for mixing the series of the IC's i didn't know that.. would be more careful when looking up the datasheet and choosing my IC's.
    oh my god i learnt more things you from you guys in one day than my teacher alone teaching me nothing for the last few months..
    i'm really thankful for all the extra knowledge you guys contributed :)
    really appreciate it guys! thanks!

    and as for the under described title, my bad.. wont happen again :D thanks for the help guys!
     
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