led sequence

Discussion in 'The Projects Forum' started by andreapg, Aug 14, 2010.

  1. andreapg

    Thread Starter Active Member

    Feb 2, 2010
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    Hi,
    That schematic should work for a 8 led circuit, with sequence reverse, but I am not sure about the reset circuit IC3.
    When IC1 pin 11 is on, IC3 takes the high level by R21 and Q19 collector.
    When IC2 pin 11 is on, IC3 takes the low level by R20 and Q18 collector.
    I simulated it with microcap and it works fine, but I drove R17 and R19 by a normal switch; using a discrete switch may be different.
    In other words I am not sure about the resistors value, especially R17.

    On the output circuit IC1 pin 15 takes the direct signal by a 470 ohm resistor.
    What do you think about that?

    http://docs.google.com/leaf?id=0B7L...WFlZDgtNmM1Yzk4NTdlNWEx&hl=it&authkey=CPGQjEg
     
  2. Wendy

    Moderator

    Mar 24, 2008
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    Another way to display an image.

    [​IMG]
     
    Last edited: Aug 14, 2010
  3. andreapg

    Thread Starter Active Member

    Feb 2, 2010
    41
    0
    Thanks for reply
    In that image you can see the reset circuit IC3 (IC1 and IC2 are decade counter CD4017).[​IMG]
     
  4. marshallf3

    Well-Known Member

    Jul 26, 2010
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    Is this an existing design you found that you're trying to modify such that it only has 8 LEDs? If so you'll only need one of the 4017 ICs and, unless I'm missing something, it won't need to be as complex.
     
  5. Wendy

    Moderator

    Mar 24, 2008
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    I think the OP wants something back and forth. This isn't usually how it is done though, and there is an element of unnecessary complexity. Are you wanting this to scan back and forth, or are you wanting to select the direction of the scan?

    See chapter 11 on what is probably a simplier technique (if I read what you're trying to do correctly).

    LEDs, 555s, Flashers, and Light Chasers
     
  6. andreapg

    Thread Starter Active Member

    Feb 2, 2010
    41
    0
    Thanks for replies
    It isn't an existing design. It should scan 8 leds back and forth (automatic direction reverse). Maybe I could do this with a simplier circuit (I don't know the 4017 very well). But I think that one 4017 can drive 6 led back and forth, as shown here.
    At the start condition the IC3 output is off. IC1 pin 15 takes the direct signal from that output, so it is connected to the ground. IC2 pin 15 takes the inverted signal, so it is connected to +9V. Therefore IC1 starts scanning from L1 to L8, and IC2 keeps broken on the first output (not used).
    When IC1 pin 11 is activated the output of IC3 takes the high level; IC2 starts scanning from L8 to L1, and IC1 keeps broken on the first output.
     
  7. andreapg

    Thread Starter Active Member

    Feb 2, 2010
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    I modified the schematic, such that the 2.2K resistor (now R19) takes the direct signal from IC2 pin 11, instead of using the Darlington technique.
    But I have a question: if a 4017 output is on the low level, is it connected to the ground, such as a 555 output?

    [​IMG]
     
  8. Wendy

    Moderator

    Mar 24, 2008
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    The short answer is yes. The connection is low current, but if this requirement is met it is very stable.
     
  9. andreapg

    Thread Starter Active Member

    Feb 2, 2010
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    To prevent a reverse current flow through R19 I would use a diode, but I don't know if any type of diode works fine.
     
  10. Wendy

    Moderator

    Mar 24, 2008
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    One of the reasons I haven't jumped in a bit deeper (I tend to like this kind of circuit) is figuring voltages and voltage trip points is a major pain. This design is probably OK, but it has strong elements of analog where I tend to use digital. The link I gave you is digital, and has been verified many times.

    A diode will probably work well, but I don't know if the 0.6V drop across it will interfere with your other trigger points. A quick guess is yes, it will work, but it is only a guess. I haven't put the time into really studying this circuit to see if it will work.

    Have you built it?

    You want 8 LEDs sweeping back and forth. If you want I can show you how to modify my design to do the same thing. With some slight modifications you can also add special effects, such as delays in the LEDs going out. My article, LEDs, 555s, Flashers, and Light Chasers (forum edition), is being rewritten to show how to add these special effects.

    If you want a different number of LEDs I can show that too.
     
  11. andreapg

    Thread Starter Active Member

    Feb 2, 2010
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    0
    Thanks for suggestions.
    At the moment I have simulated it, but a real circuit may be different. I used a second 555 output istead of IC2 pin 11 (I didn't find the 4017 in the component library).
    When "IC2 pin 11" switches off I notice a reverse current peak, so the 555 backs to the high level.
    However a digital circuit is the best way, but I should learn more about 4017IC.
    For example, what happens if pin 13 is connected to the positive?
     
  12. Wendy

    Moderator

    Mar 24, 2008
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    Pin 13 is a ENABLE pin, think AND gate with an inverter in front, so a high (not a low) disables the clock pin.

    4017 datasheet

    Look at page 6.

    Something I do with my PaintCAD package, I have a folder where I put datasheets for easy reference.
     
    andreapg likes this.
  13. andreapg

    Thread Starter Active Member

    Feb 2, 2010
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    I have deleted some analog elements. At the start condition IC1 pin 13 is connected to the ground because it takes the direct signal from IC1 pin 11; IC2 pin 13 is connected to +9V by the inverted signal.
    So IC1 starts driving the leds from L1 to L8, until its pin 11 takes the high level.
    IC2 drives the leds from L8 to L1. When its pin 11 is activated the circuit backs to the start condition.
    https://docs.google.com/leaf?id=0B7LPpongh6DzMTM0ZDk5NGEtNTVjYi00MTNhLThhY2ItNjY2Y2FiZjk5OTE0&hl=it
     
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