BCD to Decimal decoder

Discussion in 'General Electronics Chat' started by jpanhalt, Oct 13, 2008.

  1. jpanhalt

    Thread Starter AAC Fanatic!

    Jan 18, 2008
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    BCD to decimal decoders are common, but the ones I have looked at all have logic high/low states. Is there such a decoder that instead has a high-impedance (i.e., open) state and low state?

    John
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
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    The high-impedance state is intended to isolate the logic element from the system. What would be the point?
     
  3. Wendy

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    Mar 24, 2008
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    Open collector?
     
  4. jpanhalt

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    Jan 18, 2008
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    Bill,
    Open collector will work, I think. Is there a family that is open collector?

    Beenthere,

    At an abstract level, one can have: yes, no, and don't know/doesn't matter.

    At a concrete level, I am playing with a set of resistors to make a digitally selectable output for a voltage regulator. The schematic has been shown on this forum. This is from the ST L200 datasheet:

    [​IMG]


    That works easily with, say, 4 discrete values. I want to select voltages between 22 V and 12 V in 0.1 V steps. An ovbious way to do that is with BCD thumbwheel switch and BCD to decimal decoder on the board. By using either transistors or blocking diodes, I think I can get it done, but an open collector type of logic chip would make it easier.

    John
     
  5. jpanhalt

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    After morning coffee, I was inspired to do more searching. It appears the SN74145, 54145, and 74LS145 are open collector.

    Any others?

    John
     
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