Mapping 4017 output to LEDs

Discussion in 'The Projects Forum' started by wayneh, Oct 21, 2014.

  1. wayneh

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    Sep 9, 2010
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    I'm designing a PCB [double-sided protoboard] using a 4017 with all its outputs used to illuminate LEDs in counting order. Does anyone have a trace/wiring layout already figured out for this? I want minimal space, short traces/wires and so on. I want the LEDs all in one column, probably parallel to the 4017 but I have some flexibility to make it perpendicular if that saves space.

    I can obviously get to this myself eventually but this chore has to have been done by others a zillion times already.
     
  2. mcgyvr

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    Oct 15, 2009
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    Oh.. thats cheating.. :)
     
  3. wayneh

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    Haha, isn't that what we do here?
     
  4. MrChips

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  5. wayneh

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    Sep 9, 2010
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    Awesome. I'll look that over. Why do they use a resistor on each LED instead of a single resistor on the ground line for the LEDs? Only one at a time will be lit.
     
  6. Bernard

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    All Electronics, CAT# AEC, LED Chaser KIT , $ 6.50; 555 & 4017, PCB, & allparts.
    This one uses one LED I limiting R.
     
  7. wayneh

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    Those are good suggestions but neither layout uses the 0.1" perfboard layout, so I brute forced my own layout. I'm not super happy with it - too many wires - but it's not obvious to me how I could improve on it.

    Screen Shot 2014-10-22 at 11.37.59 AM.png
     
  8. ScottWang

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  9. wayneh

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    I made no cost judgement (except to raise an eyebrow at all those resistors). It's just that the PCB trace layout doesn't apply directly to my perfboard, so I chose to do my own layout.
     
  10. SgtWookie

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    Jul 17, 2007
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    In the commercial board, they used resistors for both limiting current in the LEDs, and as jumpers across traces. Yes, you really only need a single resistor, since only one LED can be on at a time - but you'll still need jumpers due to the IC's pinout and your board layout requirements. Resistors are really, really cheap when bought in quantity - and make for good jumpers when required.
     
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