100 LED chaser

Discussion in 'The Projects Forum' started by Ron H, Feb 17, 2013.

  1. Ron H

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    Has anyone ever posted, or seen online, an LED chaser (one direction, one LED at a time) that will handle up to 100 LEDs while requiring only two CD4017s, plus 20 transistors and a handful of resistors? The length can actually be arbitrary.
    As with all chasers, it also needs a clock oscillator, and maybe a power-on reset, both of which are made here with a Schmitt trigger quad NAND package.

    I'll post the basic 100 LED version here. The arbitrary length version requires a few more parts.

    If this is a common approach, I hope you'll forgive my ignorance. I am not an LED chaser guy, normally.
     
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  2. Wendy

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    Ummm, I'm stealing this. OK? I'll probably add it to my light chaser article.

    You can set an arbitrary count with a very simple diode AND gate. Easy peasy.

    If you are going to use driver transistors I would also add sinking transistors to get the full benefit of current amplification.

    I really love this, it is neat.
     
    Last edited: Feb 17, 2013
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  3. Ron H

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    Sure. Credit would be nice.:)

    That was my plan, although if you want to retain the power on reset, you also need to OR the original one with the output of the AND gate.

    Sinking transistors drive the rows. Sourcing transistors drive the columns. Am I missing your point?

    BTW, for the benefit of NOOBs: The LEDs can be arranged in any geometric fashion, such as a line, a circle, etc.
    If you need a shorter chaser, unused transistors and resistors can be eliminated.
     
  4. Wendy

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    Full name or just forum link? I understand wanting credit, just tell me how you want to be listed. If you don't want to do it here send me a PM. That way only folks who only read the article will know (whatever there is to know).

    In your drawing you have the Vcc 4017 providing all the current, I suspect this will still limit it to 6.8ma, though I would have to check the data sheet to be sure. A simple emitter follower for each output will solve this problem.
     
  5. Ron H

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    Are you looking at the same drawing that I am? Both 4017s have transistor buffers. The LEDs run at ≈20mA.
     
  6. Wendy

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    My bad, I did miss the other set of transistors. So stealing it as is it is then (but you will get the credit).

    If you don't mind I am hijacking this thread, rather than starting a new one, to explore this circuit further. Long term I may even come up with a PCB for the basic designs and post them here, and then there is adapting it to sweep back and forth.

    This one will keep me busy for a while.
     
  7. Ron H

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    That's gonna be tough, unless you can find (or make) an up/down Johnson counter/decoder.

    I would love to see a PCB. I was thinking a circle would be cool. I think it would require a double-sided board, or a lot of jumpers.
     
  8. Ron H

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    Can you explain why you say that?
    The transistors are emitter followers. They don't need base resistors.
     
  9. Wendy

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    They are common emitter, high impedance in, low impedance out. Basic stuff.
     
  10. Ron H

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    I think you mean common collector.:)
     
  11. Markd77

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    It's the 300 ohm resistor R11 at the very bottom that limits the base current in the transistors Q11-Q20. No reason to use PNPs.
     
  12. Ron H

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    We have LEDs that have a fwd voltage of 2 or 3 volts. We have a 9V supply. Somewhere, we have to drop an extra 6 or 7 volts. I chose to drop 0.7V across an emitter follower. The remaining drop is across R11. This is more efficient than a PNP. With a PNP we would have to have a base current limiting resistor (more parts), and supply enough current to guarantee saturation (more currrent). The NPN emitter follower base current is automatically limited by beta. Furthermore, PNPs would require 10 inverters, since the pulses are the wrong polarity.
     
    Last edited: Feb 17, 2013
  13. vrainom

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    Amen to that. There are a lot of ways to do things and it's fun to think about the different ways to get to a solution.
     
  14. Wendy

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    I will probably make a uber simple LED grid just to demonstrate this. It also solves another problem I've been mulling for several years, I want to make a digital LED clock that looks analog, 60 seconds, 60 minutes, that kind of stuff. The parts count is satisfyingly low with this.

    I'm thinking of a simple 20 pin ribbon connector to connect two boards together. It would make modifications pretty easy.

    So it is. I'm thinking of steering diodes for a sweep, though I'm not sure the idea will work. Gives me something to think about walking and driving.
     
    Last edited: Feb 18, 2013
  15. GopherT

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    You could use a multiplexer and counter instead of a 4017.

    74HC4067 multiplexer allows 16 outputs so two could control a 16x16 array.

    The multiplexers need a counter. Interestingly, one 8 bit up/down counter (DM74LS469 for example), could drive both multiplexers. the lower four bits to drive one multiplexer and the upper 4 bits could drive the other. That way, you could travel across x-axis 16 steps (bits 0-3), then index on the y-axis when the higher 4 bits increment. This device allows up/down counting by toggling the U/D bit.

    Alternatively, separate 4-bit counters could be used to drive x and y position separately (or use bdc counters if you want to limit to a 10x10 matrix and still use the above-listed multiplexers).
     
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