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Thread: Johnson counter

  1. #1
    Ybody Newbie
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    Default Johnson counter

    There is probably an extremely easy way of doing this that I am missing.

    Using a 4017, I am able to verify my counting works by breadboarding some LEDs to the respective outputs.

    I have a stopwatch that requires a low to start and another low to stop. Normal stopwatch, so if the low never goes high, it will still be timing. As it stands right now, once output 0 goes from high to low, the timing starts. It cycles through all the other LEDs and the stopwatch continues running. Go back through the cycle, LED 0 lights up and as it goes out, the timer stops timing. Say I want it to start on the dropout of LED 0 and stop on the dropout of LED 8...

    Code:
    |   4017   |
    |__________|
    0 1 2    8 9
    |        |
    |        |
    R1       R1
    |        |
    LED      LED
    |_*____*_|
         |
         |
         SW
         |
       Ground
    
    Should I just pop 2 diodes in where the "*"s are or is there a better way of doing this? SW is the stopwatch connection to the start/stop button. This is my first shot at this, and after about a day and a half of 4017 and quad comparitor searching, mind mind is pretty much fried. TIA


  2. #2
    Super Moderator kinjalgp Newbie
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    Default

    Since LED is also a diode, you don't require any additional diodes.
    "There is no way to peace, peace is the way!"

  3. #3
    Super Moderator mechie Good mechie Good
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    Default

    Edited for stupid mistake ops:
    The best way of dealing with this (depending on what you want) is...
    Use the LEDs as the 'OR' gate - move the resistor to further down the circuit
    -- still loses about 2v across the LEDs

    Better to use signal diodes (1N914 or similar) as the 'OR' gate then the LEDs can be omitted if required
    -- only loses about 0.7v across diodes
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  4. #4
    Super Moderator kinjalgp Newbie
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    Use the LEDs as the 'AND' gate
    Two diodes, with their cathodes shorted will form "OR" gate not "AND" gate. The output will be logic 1 even if anode of any one diode is at logic 1. And thats the truth table of "OR" gate.
    "There is no way to peace, peace is the way!"

  5. #5
    Sebi Newbie
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    The two diodes can work as AND gate with reverse polarity, and pull-up resistor in common anode....

  6. #6
    Super Moderator mechie Good mechie Good
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    Default Dho !

    Sorry guys --- you got me :!:

    The diagram is correct
    My waffle is wrong ops:
    Not thinking before I rattle my keyboard -- I meant 'OR' gate, honest :roll:
    ....................Original post corrected !
    I need a memory upgrade ...
    My head is full !

  7. #7
    Super Moderator kinjalgp Newbie
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    Quote Originally Posted by Sebi
    The two diodes can work as AND gate with reverse polarity, and pull-up resistor in common anode....
    Yeah ,thats true!
    "There is no way to peace, peace is the way!"

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