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Wiring boolean gates

  1. Jan 24, 2005 #1

    eax

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    Is it possible to wire a 'invert gate'. 'AND' gate is easy to wire

    Code (Text):

    VCC
    |
    |
    ----------------out
       |   |
       |   |
       |   |
       A   B
    ----------------GND
     
    If a or b or both are grounded (is 0/low) then output is 0. No matter how hard I try I still can't build a circut that will function as a 'NOT' gate. Anyone know how to wire a 'NOT' gate?

    Thanks in advance!
     
  2. jcsd
  3. Jan 24, 2005 #2
    the "not" gate is one of the main gates. Isn't it a single gate on it's own, looking like a sideways triangle with a little circle at the end?
     
  4. Jan 24, 2005 #3
    I don't know what you are trying to do, but a 7400 NAND gate can easily be used as a NOT gate by simply tying the two inputs together and using them as a single input.

    I'm not sure how you would wire an AND gate to behave as a NOT gate if that's what you are trying to do.
     
  5. Jan 25, 2005 #4

    eax

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    Iam trying to wire the circut of a 'NOT' gate using wires not other "pre wired" chips such as 74...
     
  6. Jan 25, 2005 #5
    I can see wiring up an AND gate or an OR gate using just wires and switches. But I don't see how you could wire up an effective NOT gate without at least using a relay.

    Unless you simply take a switch and just re-label it's ON and OFF labels so that it does the opposite of what it says it's doing. :rofl:

    Seriously though. How else are you going to do it?
     
  7. Jan 25, 2005 #6
    Here you go,... Logic Gates

    This site just uses N.O. (normally open) and N.C. (normally closed) push-button switches.

    They simply call the N.C. switch a NOT gate. When there's no signal (i.e. the button is NOT being pressed) then the output is high. If there is a signal (i.e. the button is pressed) the output goes low.

    This is basically the same thing that I've suggested about having the switch do the opposite of what it is marked. (i.e. pushing it turns it OFF vs. pushing it turns it ON.)
     
  8. Jan 28, 2005 #7
    You cannot wire any combination of AND gates to produce a NOT function. However, you can come up with any function using a single or combination of NAND gates with the possible exception of XOR and XNOR. But I could be wrong on that last part.
     
  9. Feb 11, 2005 #8
    hes asking how to make a NOT gate from scratch. if you think for a few minutes u can figure out how to create an AND or and OR gate simply with 2 transistors, but how do you construct a NOT gate? ive been trying to figure this out myself. this is assuming u cant use switches - aka the input is from the output of another gate. how would you invert this using transistors, diodes, etc (no mechanical devices such as a relay)?
     
  10. Feb 11, 2005 #9
    YOu're trying to do this with just wires and switches? No use of relays or solid state devices (transistors, diodes, ect...)
     
  11. Feb 11, 2005 #10
    how do u do it with solid state devices but NO relays?
     
  12. Feb 14, 2005 #11
    Don't know, that's why I'm asking.
     
  13. Feb 20, 2005 #12
    you can do it with a resistor and a transistor as follows

    . vcc
    . -----
    . |
    . R
    . |
    . Vin-----T
    . |
    . -----
    . gnd

    hope thats clear.
     
  14. Feb 20, 2005 #13
    Yeah, I believe that NOTs are the simplest gates. They're basically a single transistor, along with any resistors appropriate to preventing it from burning, of course. Basically, all you have to do is connect the input voltage across the base and emitter, and take the output voltage across the collector and emitter. If the input voltage is high, current will flow through the transistor, and there won't be a large voltage drop across the collector and emitter: hence, the output voltage is low. Conversely, a low input voltage will not allow current to flow, and the output will be high. Thus, we have a NOT gate.
     
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