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Power issues with latches

Discussion in 'General Electronics Discussion' started by JTeach, Oct 6, 2014.

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  1. JTeach

    JTeach

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    Oct 6, 2014
    Hello! I'm trying to create a basic rock paper scissors simulator as a project for a group learning about latches. We're going to be using the CD4044BC NAND R/S Latch IC. I've been working on trying to breadboard up a basic circuit in advance of the project, however I can't seem to get the latch to function properly. I've been using a 9V battery for both powering the chip and the inputs. Not only has the latch not been working, but making contact with the wires causes the LED to light (and I don't mean because the wire is loose, it is the contact/proximity of my finger that causes it). My best theory is it has something to do with stabilizing the power, but my electronics background isn't strong enough to figure it out on my own. Hoping for a little help.

    Thanks!
     
  2. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    Sounds like you may have floating inputs.

    CMOS inputs are very high-impedance, so if they aren't connected (or pulled, with a resistor) to a known voltage level, they will float, assume random states, and pick up noise.

    Why the CD4044? It's a pretty uncommon device.
     
  3. JTeach

    JTeach

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    Oct 6, 2014
    Right! I've had that problem before and it didn't even occur to me. Thanks I'll give it a shot.

    As for the chip, We use Multimedia Logic for a lot of our instruction and basic design. I wanted something that would be an easy transition for the students. That was what I came across in my google adventures. I'm open to other suggestions if you have something simpler or more common.
     
  4. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    Well, the CD4013 is much more commonly used, but you only get two latches per package, not four. Also, the set and reset inputs are active high (like the 4043, which is like the 4044 but with active high inputs instead of active low inputs).

    I guess the 4000 series is all close to obsolete now (apart from a few special functions like 40106, 4093, 4046, and 4060 that are still pretty useful), so it probably doesn't matter which one you use!
     
  5. JTeach

    JTeach

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    Oct 6, 2014
    The other one I have on hand in our supplies is the NOR MC14043B. Any advantage to using that instead or is it a toss up?
     
  6. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    That's the 4043 that I mentioned. The only difference is that the 4043 has active high set and reset inputs, and the 4044 has active low set and reset inputs. Active low inputs are more common in the 74xxxx devices; most 4000 series devices use active high logic. But I don't think it really matters. Your students have to learn the concept of active high and active low anyway.
     
  7. JTeach

    JTeach

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    Oct 6, 2014
    Thanks for your help. I managed to get the 4043 working today (the 4044 still seems to have it in for me) but that's enough for me to keep moving forward. Maybe I'll beat it into submission at a later date. Thanks again!
     
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