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why do we use these

Discussion in 'Electronic Basics' started by dhana, Oct 24, 2006.

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  1. dhana

    dhana Guest

    what is the use of composite signal generator, zero crossing detector
    and comparator
  2. Eeyore

    Eeyore Guest

    How long is a piece of string ?

    Perhaps you'd like to put these in some context ?

  3. John Fields

    John Fields Guest

  4. I believe that is the correct answer, since I was thinking of posting
    an almost identical reply.

  5. Bob Myers

    Bob Myers Guest

    1. Composite signal generators are used in those applications
    where all-metal ones would be too heavy.

    2. Zero crossing detectors are used when it is important to
    recognize and/or count the number of zeroes which cross
    one's path. In many cultures, having your path crossed by a
    zero is analogous to our beliefs regarding a black cat crossing
    your path.

    3. "Comparator" is a term which derives from the same Latin
    root as the word "compose," i.e., it is a device which puts
    stuff together, as opposed to a "separator," which of course
    takes stuff apart.

    Best of luck on the homework!

    Bob M.
  6. PeteS

    PeteS Guest

    This is important in some areas because zeroes are slippery and can
    wiggle through where a one can not. The ones may get stuck in the bit
    grate, whereas the zeros can slither through. Counting these is
    important in defining the efficacy of a bit grate (measured, of course,
    in it's duty cycle).


  7. JeffM

    JeffM Guest

    You guys slay me. :cool:
    These rate with some of my favorite respones to homework trolls:*-Fields+textbook+*-megohms*-*+zz-zz+your-teacher-*-*-*+qq-qq+*-*-exist

    A previous one from Pete:*-having-to-think
    Now that the accounting industry has oversight,
    it appears the lazy, corner-cutters are trying to find other fields.
  8. JeffM

    JeffM Guest

  9. PeteS

    PeteS Guest

    I had been considering writing an authoritive guide on 'How to post your
    homework questions to s.e.b and s.e.d', but I never got past the first
    paragraph as I kept snorting my wine on the keyboard.

    Now there is the possibility I could write such a thing while not
    drinking wine, but that would remove any real point ;)



  10. We need a real, nice "Homework helper FAQ" for the sci.electronics.*
    newsgroups. Maybe we could all use up lots of puns before they go
    stale? ;-)

    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
  11. feebo

    feebo Guest

    a zero crossing detect circuit is used to indicat when and AC voltage
    is crossing the 0V line or within a window of a few volts either way.
    You know that AC voltages swing to a positive voltage and then a
    negative and this repeats continuously right?

    If you are switch something on, at the point the current starts
    flowing, it can make "noise" both electrically and within the radio
    spectrum (you may have seen this as lines of interference on your TV
    when someone has gone past on a motorbike or similar - the Radio
    interference from the ignition circuit is temporarily swamping the TV
    signal and being displayed as rubbish on the screen). So, if you turn
    on an AC device, you generally don't have any idea where in the swing
    cycle the voltage is and if it is significantly in, current will
    "rush" in to the device - with the same effect as the motorbike.
    Dimmer switches on lighting that don't use resistors use a triac to
    switch to the voltage on and off rapidly - because the bulb take a
    while to reach full brightness, if you switch off the power before it
    gets there it will appear to be dim constantly, but if you do this
    without a zero crossing trigger of some sorts it will play merry hell
    with your electrics and TV. A zero crossing detect will tell when it's
    safe to switch the power on... because you are at zero voltage, there
    is no current flowing (actually there will be a bit because 0v lasts
    for a fraction of a second) so you allow the curretn to build up
    nicely with the voltage. You can turn the power off anywhere in the
    cycle with minimum interference.

    So to recap, ZCD lets you know (in this application) when to switch
    the power on to eliminate electrical and RF noise (also stops


    A comparator lets you compare two voltages. One is usually a reference
    and the output of the comparator will be at 0v so long as the input
    voltage remains less than the reference. as soon as it is more, the
    output will go "high" (to the positive supply voltage). A window
    comparator will have two references and the output will go high only
    when the input voltage is in between those - you could make a ZCD out
    of a window comparator - if you set the lower reference to same -0.5v
    and the upper to +0.5v, the output would go high breifly for the time
    the imput voltage was between these two levels (right around 0v)
  12. feebo

    feebo Guest

    but this is a "basics" NG
  13. JeffM

    JeffM Guest

    When you subsidize a behavior, you get more of it.
    If the OP is too lazy to pay attention in class or to learn to use
    a failing grade is apt.
    Please don't feed the homework trolls.
  14. JeffM

    JeffM Guest

  15. feebo

    feebo Guest

    I hear what you are saying Jeff, and while I do agree that this is
    probably someones homework I chose to give the benefit of the doubt.
    Certainly if this had been posted anywhere but SEB I would have
    ignored it.

    I'll try to be a bit more discerning in the future but I remember what
    a mystery it all was (and a lot still is) all those years ago - I
    couldn't even find someone to tell me how the pins on a transistor
    related to the connections inside the circle (which was the emitter) !
    so much water under the bridge since then :eek:)
  16. PeteS

    PeteS Guest

    I was thinking on the lines of a non-FAQ (mild sarcasm mode) thus:

    Title: The title of your question is all important. To get the attention
    of the people who can answer your question, you need to make it stand
    out. Known methods of doing this:

    2. Reference a current political problem
    3. Ensure it is indecipherably vague.
    4. Use 733t 5p34k, or txt spk


    Are Republicans to blame for my project?
    Confubulator fries?
    Cn U Hlp wth prblm?

    and so forth ;)

    and then perhaps a serious (well, mildly serious) one afterwards that
    gives real guidance. Make it through the first part and one is rewarded :)


  17. PeteS

    PeteS Guest

    I think what JeffM (and myself) are saying is we help those who have
    tried to help themselves :)

    I will definitely help with homework *provided the OP has tried to solve
    the problem already* and is perhaps stuck on phraseologu or perhaps a
    somewhat murky chapter in a text.

    To paraphrase, _We help those who help themselves_



  18. Just make sure that they learn to ask, "Doyahal want fries with
    that?" ;-)

    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida

  19. All the others are to proceed to the closest fast food place to apply
    for their job in their lifelong career in the food service industry.

    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
  20. PeteS

    PeteS Guest


    I know we all agree, but many an OP doesn't seem to realise that if you
    don't do your own work, you really won't learn anything. There are some
    professions where this may, in fact, be desirable. Engineering
    (especially design engineering) isn't one of them ;)


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