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Homework Help: Adjustable AND-logic unit?

  1. Apr 1, 2008 #1


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    Hello all,

    I'm designing logic unit, but unfortunately I realize I have a lack of skills straight away at the beginning.

    The task is to design a unit which have five inputs and one output (all standard TTL). The Unit should be adjustable, so user can choose number of coincidences needed to have a logic high output signal, from one (works like or gate) to all five inputs are at a logic high.

    In a nutshell, how am I planned to make this happen: At first to use basic summing amplifier to sum input signals. In theory there is no upper limit to the number of input signals, but should I notice something to make it work very well becouse I have as many as five input signals? By using proper values of R_f/R_in I can make sure not to exceed output voltage range.

    Then by using comparator with an adjustable (five steps, using some rotary switch) reference voltage choose a desired amount of coincedences. Supply voltages up to +-24V are on hand.

    Is this at all a workable method?

    I got other idea from much more experienced designer to use a diode logic. The diode logic would be really easy if only as many inputs as needed to logic high are used. But now pulse could come from any input. How can I avoid a huge number of components when I have to take care of all possible combinations?

    So, is there any sense to do it this way? How would you do it? All tips and hints are very welcome.


    ps. sorry about the long parttling but I wanted to show you that I have at least little bit thought this problem before asking your advise :)
  2. jcsd
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