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Hardware Freedom Day is April 20th!

fustini

http://www.hfday.org/images/mightyohm.jpg

Hardware Freedom Day is a yearly celebration of Open Hardware! Every year since 2004 hundreds of teams have been celebrating Software Freedom Day, often showcasing Open Hardware in the process. At the Digital Freedom Foundation(formerly known as SFI) we thought it was about time to have a special day just for Open Hardware. So get your hackerspace in order, your team up to speed and register your event right now!

You can find if there is an event planned near you:

 

http://www.hfday.org/map/

 

or learn how to organize one if not:

 

http://wiki.hfday.org/StartGuide

 

Anyone planning to go to one or organize one?

 

cheers,

drew

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  • in reply to billabott

    I don't think the given condtions are inconsistent, but I think the first condition,

    If El Paso is open, then Phoenix and San Diego must both be either open or closed.

    could be simplified to just

     

    If El Paso is open, then Phoenix and San Diego must both be closed.

     

    So the "or open" is superfluous/redundant, because it can never happen, but that doesn't make it inconsistent.

     

    However, I am troubled by the first row of the truth table.  I would have expected T=1 because

    neither condition is violated.

     

    I'm also confused by the Tuscon pipe.  I would have expected that the flow in the Tuscon pipe

    would be the sum of the flows in its 3 feeder pipes, but clearly that isn't what column T represents.

    There seems to be an implied condition that the Tuscon pipe flows if and only if the 2 conditions are

    satisfied and at least one of the feeders is flowing.

  • in reply to Former Member

    coder27 wrote:

     

    I don't think the given condtions are inconsistent, but I think the first condition,

    If El Paso is open, then Phoenix and San Diego must both be either open or closed.

    could be simplified to just

     

    If El Paso is open, then Phoenix and San Diego must both be closed.

     

    So the "or open" is superfluous/redundant, because it can never happen, but that doesn't make it inconsistent.

     

    However, I am troubled by the first row of the truth table.  I would have expected T=1 because

    neither condition is violated.

     

    I'm also confused by the Tuscon pipe.  I would have expected that the flow in the Tuscon pipe

    would be the sum of the flows in its 3 feeder pipes, but clearly that isn't what column T represents.

    There seems to be an implied condition that the Tuscon pipe flows if and only if the 2 conditions are

    satisfied and at least one of the feeders is flowing.

    I agree that the Givens are inconsistent.  The first given is OK as written: it says that if El Paso is open, the other two are equal (exclusive NOR).  However, the second given conflicts with the first, because if El Paso is open then both Phoenix and San Diego could be open, but if Phoenix is open then El Paso must be closed.  It appears to be one of those examples that's so simple that its author didn't think he or she needed to check it.

  • in reply to johnbeetem

    John,

       What do you call a boolean logic condition that says

          A implies (False or B)

    Clearly the False is redundant and the condition could be simplified to

         A implies B

    But I wouldn't call that inconsistent, because you wouldn't have any trouble creating

    a unique truth table for it.

     

    In the original example we have

         E implies ((P and S) or (~P and ~S))

         P implies (~E and ~S)

     

    The first condition can be simplified (in light of the second) to

         E implies (False or (~P and ~S))

    which can be simplified to

         E implies (~P and ~S)

     

    which leaves you with two consistent conditions that make for a unique truth table.

     

    It wouldn't surprise me if the author unintentionally had a redundant (P and S) in

    the first condition, but I don't see that it really matters at all.

  • in reply to Former Member

    Assuming that the site http://www.digilogwiki.com/index.php?title=Minterms_and_Maxterms is intended to be tutorial, it's very important to avoid verbiage that might be contradictory.  For that matter, one could interpret:

    If El Paso is open, then Phoenix and San Diego must both be either open or closed.

    to mean that Phoenix must be either open or closed, and San Diego must likewise be either open or closed.  Since there's no "partially open" in Boolean algebra, then Phoenix is always either open or closed, and San Diego is always either open or closed, so they both simplify to TRUE, so the whole given simplifies to "if El Paso is open, then TRUE".  Not amusing enough to be a sillygism, so it's just confusing.

     

    They also neglect to say whether 0 means open and 1 means closed, or vice-versa.  You need to know this to construct the truth table.

     

    It's hard enough to learn logic without trying to make sense of ambiguous examples.  In particular, the premises have got to be clear and unambiguous.

  • in reply to johnbeetem

    agreed, the example is anything but clear and unambiguous!

  • in reply to Former Member

    Working backwards from the truth table, I have concluded the the Givens need to be changed from

    If El Paso is open, then Phoenix and San Diego must both be either open or closed. If Phoenix is open, then both El Paso and San Diego must be closed.

    to

    If El Paso is open, then Phoenix and San Diego must both be either open or closed. If Phoenix is open, then both El Paso and San Diego must both be either open or closed.

     

    Happy Trails

  • in reply to billabott

    Bill,

       I think you're on to something.  Your change would make the last row of the truth table make sense.

    But the first row still wouldn't make much sense.