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watering system, second attempt.

Discussion in 'Electronic Basics' started by andy, Aug 4, 2004.

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  1. John Fields

    John Fields Guest

    You can do it by holding the inactive (at the moment) input at the
    level it needs to be at to allow the other input to trigger. Look at
    the truth table; it's all there.

    Also check "Watering controller 4" on
    alt.binaries.schematics.electronic for a four-chip solution that
    should give you everything you want, including a two hour holdoff
    BTW, your 4538 RESET inputs are shown floating last time I looked at
    your schematic. Not good; they need to be tied high if you're not
    using them. Also, there's no such thing as a 340K pot, you don't have
    the "B" sections of the comparator and the one-shot pinned out
    properly, and I think you're going to run into leakage current
    problems with that 1000µF cap. Plus, how about if you knock off that
    annoying little passive-aggressive trick of not using upper-case "I"'s
    where you should?
  2. John Fields

    John Fields Guest

    It's doable, but you're right. You'd have to introduce extra circuitry
    to remember what happened last and set up the inputs to react to
    what's going to happen next. Hardly worthwhile with another entire
    one-shot in the package left to do it with.
  3. andy

    andy Guest

    I can see how to trigger on one or the other edge, but not both with the
    same 4538, without using extra circuitry to make more edges or delays like
    in the first design with chips I drew. As far as I can see, the 4538
    triggers on a rising edge of the OR gate's output, but how can any
    combination of gates on the light level signal make two rising edges where
    there's only one in the signal?
    I found the text of your post on a free news server, but not the
    schematic. My ISP doesn't do binaries, so it's not easy to read this group.
    Thanks. I did remember this when I actually built it.
    That I didn't think of - thanks.
    That's partly just laziness/easy typing, but I know
    what you mean.
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