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Please, help: 470ohm resistor and 1.5V LED draw more current than 470ohm resist — Parallax Forums

Please, help: 470ohm resistor and 1.5V LED draw more current than 470ohm resist

IceFireProIceFirePro Posts: 86
edited 2010-06-18 21:54 in BASIC Stamp
I calculated this using the Ohm and Kirchoff's law's. But I am afraid to "give it a try" so not to burn something down (like an IO pin on BS2). Please, verify if this makes sense - to me, at first, it looks like it should be just about the opposite, but when I calculate it, that's what it looks like.

Comments

  • PJAllenPJAllen Banned Posts: 5,065
    edited 2010-06-18 12:49
    I am against spoon-feeding.·

    It's super-irritating asking all of these lamer questions which could be answered by opening your eyes and applying yourself (i.e. "cracking the books"),·but you·just won't take a hint.· Look at the last two or three pages --·it's all you, man.· What's the deal?

    The Stamp has a 5V "output".· The LED has a forward voltage of 1.5V, nominally, when it's "on."· The rest of the voltage, 3.5V,·has to be somewhere --·it's across the resistor.· So, that's 3.5V / 470 Ω = 7 mA.
  • Mike GreenMike Green Posts: 23,101
    edited 2010-06-18 15:29
    All you need is an LED and a resistor (and 4 AA cells in a battery pack for a 6V power supply). The worst that can happen is that you'll destroy the LED and run down the batteries. These days LEDs are cheap cheap cheap. You'll learn a lot. Go to RadioShack and buy a couple of different color LEDs if you don't have them already and try them out.
  • ercoerco Posts: 20,257
    edited 2010-06-18 15:34
    @PJ: Agree 100%. IFP needs to stop endlessly asking questions and blow a few IO pins to pay his dues. Once he breathes in the newly-released magic smoke a few times, he'll strive to understand things on his own.

    If you wanna make an omelette, you gotta crack a few eggs.

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    ·"If you build it, they will come."
  • sumdawgysumdawgy Posts: 167
    edited 2010-06-18 16:52
    erco said...
    @PJ: Agree 100%. IFP needs to stop endlessly asking questions and blow a few IO pins to pay his dues. Once he breathes in the newly-released magic smoke a few times, he'll strive to understand things on his own.

    If you wanna make an omelette, you gotta crack a few eggs.

    I normally don't like to be a firebreather myself.....

    But I gotta say.... someone's more than a little afraid of the shallow end of the beach.· Get on out there and let those waves tickle your legs.....or at least get your feet wet.
    That said, I feel that the purpose of a forum is to help. . . .(but not handhold.· Dang it, more firejumpin.gif.Sorry.)

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    Before you criticize someone, walk a mile in his shoes. That way if he gets angry, he'll be a mile away and barefoot. - unknown
  • IceFireProIceFirePro Posts: 86
    edited 2010-06-18 17:25
    I actually constantly do try stuff, I just want to "get" the logic behind it all...
  • Mike GreenMike Green Posts: 23,101
    edited 2010-06-18 18:32
    You will get further faster towards "understanding" by doing more experimentation, then asking specific questions about what you observe vs. what the theory says, then going back and applying what you've learned to more experiments. Sometimes you can't really "get" the logic behind something until you understand the differences between what the theory says and the "real world"TM.
  • FranklinFranklin Posts: 4,747
    edited 2010-06-18 21:54
    You also should be posting these non-stamp related questions in the Sandbox forum. ( not to imply that you should be posting these at all)

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    - Stephen
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