Multiplex 16 led using non-micro, TTL

Discussion in 'The Projects Forum' started by Mrdouble, Aug 12, 2016.

  1. Mrdouble

    Thread Starter Active Member

    Aug 13, 2012
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    0
    Hi guys,

    My project is pretty straight forward I think. I have incremental encoder and it has more detents than I want. My idea was to make a circle of LED's (16) around the encoder to indicate position. I don't want 16 traces wrapping around the pcb. My idea was to use 4 bits of 2 decade counters (would give 8 traces) but my lack of digital study is shining through. Any ideas or directions would be great. Thank you in advance
    Micheal
     
  2. Mrdouble

    Thread Starter Active Member

    Aug 13, 2012
    97
    0
    I should add that I don't need the counting portion. I have that figured out... I think :)
     
  3. AnalogKid

    AAC Fanatic!

    Aug 1, 2013
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    If by decade counters you mean Johnson counters, then I'm pretty sure I understand what you are describing. BUT, a block diagram or schematic is important. It is the way these things are discussed, and save tons of Q & A picking through details.

    ak
     
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  4. absf

    Senior Member

    Dec 29, 2010
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    504
    Is this the circuit you're looking for? Or perhaps you can put 2 pcs of 4017 onto the LED display board and save you a 4 bit counter.

    multiplex 16 LED.PNG
    Allen
     
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  5. AnalogKid

    AAC Fanatic!

    Aug 1, 2013
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    LED brightness is an issue. Two 4017's will do this, but a 4017 is good for only 4 mA. One of the two counters has to have its outputs inverted, and that can be done with NPN drivers. But the other counter outputs needs non-inverting current amplifiers, or the LEDs won't be very bright. I don't remember the current sink rating of an HC part, but the same probably is somewhat true for the circuit in post #4.

    ak
     
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