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Thread: simple LED circuit.. did i do this right?

  1. #1
    FLAC
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    simple LED circuit.. did i do this right?

    At work my image setter (large machine that laser prints on photographic film) dumps it's waste chemestry into 2 35 gallon drums that are covered by a large wooden box (mostly for asthetics).

    It's a pain in the butt to check them all the time so I rigged up a very simple circuit to light off an LED when the level gets to a certain height.

    I just want to make sure that this is going to be safe and everything before I leave it setup unattended (I've tested it.. left it to sit.. nothing got hot or anythng so i'm figuring it will be ok for now)

    i have a 9v battery with the negative lead going into the drum and cut.. then another lead going from the LED into the drum and the two are taped at either ends of a 1" piece of plastic. on the + pole of the LED a 100 ohm resister before heading back to the battery.

    Obviously the battery is going to run dead if I leave it in when the barrel is full, but my boss didn't feel safe about using a ac-dc power supply. He figures if we have to replace the battery everytime, it's not his money anyway.

    So does this all seem safe enough? I'm pretty stupid when it comes to simple circuits.. which is funny because I spent two years teaching a physics lab at a local upscale high school and this is one of the topics I actually have taught ^^;;

    Anyway... someone who knows what they are talking about, please respond
    aka Kumaneko
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  2. #2
    Raw Wave wizardPC's Avatar
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    does this waste conduct electricity?

    an AC-DC power supply should be fine, because the transformer won't allow more than a few hundred milliamps, which is not nearly enough to start a fire (unless you use 100ga wire)
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  3. #3
    FLAC
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    Yes sir it's been fully tested.. I just wasn't sure if it'd be save to leave set up.

    Thanks for the help!
    aka Kumaneko
    "Don't make me moderate your ***!"
    Maxima of Doom - project thread - photo gallery
    mp3car system is currently FUBAR and finances do not allow for a correction of that situation
    Real computer hackers use a rotary cutting tool on their motherboard.

  4. #4
    FLAC
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    OK, the battery is definitely not going to work.. the barrells filled up over the weekend and the battery was dead by this morning (good thing I checked!!)

    My boss doesn't want to put an ac-dc power supply on it unless we can put a fuse on it.. What size fuse would I use? Do they even make fuses that small?? and also.. Where would I put the fuse? Thanks

    If anybody has an Idea for a better way of doing this I'm open to suggestions!

    Thanks!
    aka Kumaneko
    "Don't make me moderate your ***!"
    Maxima of Doom - project thread - photo gallery
    mp3car system is currently FUBAR and finances do not allow for a correction of that situation
    Real computer hackers use a rotary cutting tool on their motherboard.

  5. #5
    Raw Wave wizardPC's Avatar
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    put a 15 amp inline fuse on it. It won't ever blow, but your boss will have peace of mind. You can buy inline fuse thingys at radio shack for like $2.
    Debt as of 1/1/05: $34,354.48
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  6. #6
    Variable Bitrate spud42's Avatar
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    battery went flat because too much current draw. led only needs 10 mA current . so ....

    9v battery , 1.5v drop across led. = 7.5 volt

    10 ma current required there fore 7.5 / .010 = 750 ohms

    put in a bigger resistor and the batt wont go flat overnight

    either that or use a 555 timer to flash the led , you can still use the same principal to trigger it .
    Volvo V40 Phase 2 2002. T4 turbo upgrade.... currently no mp3 or carputer..... researching options

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