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Help with circuit

  1. Jul 27, 2006 #1
    hello im trying to make a simple red stop light circuit and im wondering if this layout would work (one set of leds is for north and other is for east) like i want when the norht side is green the east side is red and other way around and when north is yellow east is still read

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  3. Jul 27, 2006 #2


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    Welcome to PF, Marth. I can't help you with your question because electronics is not my thing. I do, however, want to compliment you for what is probably the best circuit diagram that I've seen posted in these forums.
  4. Jul 27, 2006 #3
    If you are using a 4017 decade counter, only one of the output pins will be on (therefore only one LED will be on at a time). To me, it looks like the design will cycle through every LED (staying at green 2 cycles longer).

    I think the LEDs will cycle as follows (N=North, E=East, G=Green...)

    NG - NG - NG - NY - NR - EG - EG - EG - EY - ER - Back to beginning

    I'm also confused as to why you have the diodes in series with the green and yellow LED and not with red. Is there a reason you want them in there?

    If I were to do it with the 4017 I would set MR to Q3 (maybe Q4 depending on the timing) to force the counter to go back to Q0. This would give you 4 states (Q0-Q3) corresponding to the 4 different states of the system:


    With this you would connect the following:
    Pin 3: Q0: NG and ER
    Pin 2: Q1: NY and ER
    Pin 4: Q2: NR and EG
    Pin 7: Q3: NR and EY and Pin 15: MR
    (I also don't think that 100k resistor or 6.8 nF cap are necessary)

    Its been a little while so I invite people to examine my suggestions.

    D Dean

    Of course you still need a resistor before each LED and I don't think you need any diodes.

    Also, I' may be wrong but I'm not sure that the 10k resistor between the 555 and 4017 is necessary.
  5. Jul 27, 2006 #4


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    Actually, it's a rather bad schematic, mainly because it only gives pin numbers for the devices, rather than pin names. You have to go to the device datasheets and look up what pin 5 does, for example, to even follow how it's connected.

    - Warren
  6. Jul 27, 2006 #5


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    Well, I meant for neatness and clarity, and the colour doesn't hurt. I didn't realize that the pins need to be named.

    edit: That's peculiar. I just clicked on it again (several times), and a bunch of it is missing now.
    Last edited: Jul 27, 2006
  7. Jul 28, 2006 #6


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    I looks like an attempt at diode logic.
    This is the functional equivilent of a prom chip.

    The truth table for the diode matrix needs some work.

    The 6.8nf and 100k are for power on reset. Nice touch.

    Don't know if a 4017 can drive that much current.
    Check the spec. You may need to add current drivers to the outputs.
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