Full Adder

Discussion in 'The Projects Forum' started by aj88, Sep 17, 2012.

  1. aj88

    Thread Starter New Member

    Sep 17, 2012
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    Hey guys,
    I am trying to make a full adder with these ics:
    (2) 4011 Quad Nand Gate
    (2) 4001 Quad Nor Gate
    (1) 4070 Quad Xor Gate
    (1) 4049 Hex Inverter

    Can it be done?
     
  2. ScottWang

    Moderator

    Aug 23, 2012
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    aj88 likes this.
  3. aj88

    Thread Starter New Member

    Sep 17, 2012
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    Thanks! Can you provide a schematic?
     
  4. aj88

    Thread Starter New Member

    Sep 17, 2012
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    AKA do you need to power/ground these ics or not?
     
  5. ScottWang

    Moderator

    Aug 23, 2012
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    The linked page just provided for one bit full adder.
    If you want to get more bits, you need to use 4 full adder or more.
    If you wish to get more stages, then you can connecting the Cout of the first stage to the Cin of the second stage.

    The Cin of the first stage connecting to GND.

    All ICs should connecting the Vcc and GND.

    You can search EE parts here.
    http://www.datasheetcatalog.net/

    If you wish to get more, then try it more by yourself, if you meet any problem, just post it, then let's figure out where the problem is.
     
    Last edited: Sep 18, 2012
  6. aj88

    Thread Starter New Member

    Sep 17, 2012
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    I connect all the ics to power and ground, but when I flick a switch, it shows both LEDs flashing. What do you mean by connect cin to ground?
     
  7. ScottWang

    Moderator

    Aug 23, 2012
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    Cin is the Carry Input, because there is no Carry input connected, so that pin must connecting to GND, if that pin is floating, it could be affect the S(Sum).

    If keep the input pin of CMOS IC floating, because MOSFET's high impedance Characteristic, the pin is in a astable state, it could be occur the vibration.

    All of the CMOS IC, if any input pin is no used, then it must connecting to Vcc or GND, this could make the pin in a stable state.

    The Carry input connect to GND, it means there is no Carry in, if you connect to Vcc, it means the Carry is coming.

    http://en.wikipedia.org/wiki/File:Full_Adder.svg
    [​IMG]

    Just don't forget to connect the gate as I said in #2.
     
    Last edited: Sep 18, 2012
  8. aj88

    Thread Starter New Member

    Sep 17, 2012
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    Oh I get it... if you dont add another adder, you connect the cin to ground. Does that mean that the 2nd input of the 2nd xor gate is grounded and so is the first input of the first and gate?
     
  9. aj88

    Thread Starter New Member

    Sep 17, 2012
    27
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    I also didn't ground the unused inputs of the ics, that may be a problem too. I will try again.
     
  10. aj88

    Thread Starter New Member

    Sep 17, 2012
    27
    1
    Ok, I did that and 1 LED was on, the Cout LED. I made a diagram of what my circuit looks like but I can't put it on this. Here is my email if you want the image: aj8898@aol.com If not, thanks for helping, I will try more.
     
  11. Austin Clark

    Member

    Dec 28, 2011
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    Don't forget, if you're using switches or something for the inputs, you'll still need to use a pull-down resistor. That is, use a fairly high-value resistor to connect the inputs to ground. That way, when you press a button and connect that pin to power, you're not shorting to ground, and the IC still sees the high voltage, yet when the button isn't pressed, the input isn't just "floating". Floating inputs will act crazy due to static and other interference. For example, ff you use a counter, and leave the CLOCK input floating (or, better yet, connected to a wire you're holding. Like an antenna), you'll actually be able to see it begin to count; Usually at around 60 Hz, due to mains interference. :)

    EDIT: Also, you only need to ground unused INPUT pins. If you ground output pins, when it wants to output a HIGH voltage, you'll be shorting it straight to ground, wasting power, creating heat, and even potentially damaging the IC.
     
  12. ScottWang

    Moderator

    Aug 23, 2012
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    The 2nd Xor and first AND gate had a common input pin - Cin, so grouned it if you unused.

    >I also didn't ground the unused inputs of the ics, that may be a problem too. I will try again.

    The first bad thing is increase the current dissipation.

    The second bad thing is when the floating pins occur the vibration, the vibration could be affect the others input gates of CMOS IC.
     
  13. Austin Clark

    Member

    Dec 28, 2011
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    I'm not sure what you mean by "vibration"?

    Actually, the first adder doesn't even need to be a full-adder. The first stage could just be what's called a half-adder. http://ustudy.in/sites/default/files/ALU_half_adder.gif

    It's less than half the size, and works precisely the same as a full adder with Cin constantly set to LOW, or 0.

    Also, just to be sure the OP knows, there are ICs that contain full adders all-in-one, like the 4008 CMOS IC. http://www.doctronics.co.uk/4008.htm
     
  14. WBahn

    Moderator

    Mar 31, 2012
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    You can do it with two of the gates from a quad XOR gate and three of the gates from a quad NAND gate.

    In the diagram on Wikipedia that was linked in the first response, simply replace each of the AND gates and the OR gate with a NAND gate.

    If you do this, then you can make a four-bit adder using two quad-XOR chips and three quad-NAND chips.

    As has been pointed out, be sure to supply power and ground to each chip and be sure to tie each unused input to either power or ground. The Cin input should be tied LO if it is not being used.
     
  15. Austin Clark

    Member

    Dec 28, 2011
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    I'm uploading on the OPs behalf :)
     
  16. ScottWang

    Moderator

    Aug 23, 2012
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    >I made a diagram of what my circuit looks like but I can't put it on this.

    You have to use the reply function, if you wish to upload any images.

    And then you will find the function located on lower of the messages box, as:
    Additional Options
    Manage Attachments ← choose this key to get your images that you want to upload.

    When you upload the images successful, then you just move the cursor to the image linked line, and then click right key to active the menu, and choose the function as duplicate the linked website.

    And now you can put the image on your messages box where you want to paste it.

    Choose the function - insert image, the function located on upper of the messages box(there is a mountain on it), and paste the image linked page that you already copied.

    And move the cursor to choose the place where you want to paste it.
     
  17. Austin Clark

    Member

    Dec 28, 2011
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    Last edited: Sep 18, 2012
  18. Austin Clark

    Member

    Dec 28, 2011
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    I believe you can't upload with less than 10 posts on the forum.
     
  19. ScottWang

    Moderator

    Aug 23, 2012
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    Thank you, you are right, many forums had that kinds of rule.
    But the method is still useful for anyone who want to upload the image when he over ten posts.
     
  20. Austin Clark

    Member

    Dec 28, 2011
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    Ok, if you're sure you've made your connections correctly, you've looked at the datasheets time and time again, you're sure you're powering each of your ICs serparately, and you've tested your ICs to make sure they haven't been destroyed, you may want to look at pull-down resistors for your inputs.

    I've drawn a quick sketch of what I mean by that.

    If that doesn't work, let us know.
     
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