Multiplex 16 led using non-micro, TTL

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

  1. Mrdouble

    Thread Starter Member

    Aug 13, 2012
    82
    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 Member

    Aug 13, 2012
    82
    0
    I should add that I don't need the counting portion. I have that figured out... I think :)
     
  3. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,540
    1,251
    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
    1,492
    372
    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

    Distinguished Member

    Aug 1, 2013
    4,540
    1,251
    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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