Fun little brain teaser

Discussion in 'General Electronics Chat' started by KL7AJ, Sep 22, 2015.

  1. KL7AJ

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    I ran across this ages ago, and I present it to each new electronics class as an exercise.

    You have a black box with four leads coming out of it. You apply a voltage (ac or dc) to any two adjacent leads. The two remaining leads output precisely 1/4 of the applied voltage. What is in the box?


    Eric
     
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  2. strantor

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    a wheatstone bridge with an inverted side? Like this:
    [​IMG]
    the 12V source represents your applied voltage, and points C & D represent your output leads. Potential difference between C & D is 4V (1/3 applied voltage in this case).
     
  3. KJ6EAD

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    I agree in principal but don't the resistors have to hold the ratio X:3X to satisfy the 1/4 voltage requirement?
     
  4. strantor

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    The values can be changed to make it hold a 1/4 voltage when voltage is applied from opposite corners, but when it is applied on the same side, it no longer works. So I proved myself wrong. I'll think about more tomorrow. Good night.
    wheatstone.png
     
  5. blocco a spirale

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    Here's what I think it is:

    Bridge 01.png
     
    Last edited: Sep 22, 2015
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  6. strantor

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    Nice! And you even made it look like a box!
     
  7. KL7AJ

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    Free hint: It can be done with just 5 resistors
     
  8. AnalogKid

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    If the four leads are in a row, does the outside pair constitute an adjacent pair as if the four leads were in a box?
    Or does four-in-a-row intentionally have one fewer possible connection?

    ak
     
  9. blocco a spirale

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    Version 02:
    Bridge 02.png
     
    Last edited: Sep 22, 2015
  10. GopherT

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    So, I assume "Blocco a Spirale" translates to, "Master of Voltage Dividers"

    PS: I know it is a "spiral notepad" but I like my translation better for today.
     
  11. blocco a spirale

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    I'll settle for "Master of guesswork that just happened to lead to a quick solution but may not be so lucky next time" :)
     
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  12. KL7AJ

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    Here ya go.
     
  13. blocco a spirale

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    Well, that makes sense o_O
     
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