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L.E.D. question..... beginner needing help

Discussion in 'Electronic Basics' started by Palmer Hudson, Nov 14, 2004.

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  1. I am wanting to connect 4 LED's together to a 12 volt power source....well
    to be car.
    I know that they are 1.7 volt and 20ma per LED and I need to use a 1/4 watt
    270 Ohms resistor.
    My question(s) is this:
    I think that I should be connecting the resistor to the incoming positive
    side voltage source but I don't know if I connect all the LED in parallel
    (all positives and negatives together) or series (positive to negative and
    so on) or if an LED has a negative/ positive side.
    I know this must be elementary but I"m just leaning.
    Thanks for your help.
  2. Lord Garth

    Lord Garth Guest

    Connect the LEDs in series, + to - to + to -, etc.
    R=260 ohms, use 270 ohms standard value.

    P=104mA, 1/4 watt is fine

    The problem is that the car has a higher voltage than 12 when it is running.
    It is also
    very noise electrically speaking. This can damage your LEDs. Since this
    circuit is in
    series, connect your resistor at any convenient point.
  3. peterken

    peterken Guest

    connect them in series, including the resistor, sequence doesn't matter,
    orientation of leds does
    a led usually has a short and a long leg, short one being kathode and long
    one being anode
    if equal length legs, look "through" the led, the largest (thickest) side is
    usually the "table" which is kathode
    kathode should be pointing towards gnd
    resistor value is ok
  4. Active8

    Active8 Guest

    That's kinda misleading. The *cathode* is *connected* to the more
    negative or ground side. The *anode* is sybolized by an *arrow*
    which *points* toward ground.
  5. peterken

    peterken Guest

    If looking at schematic symbols, then yes it's an arrow pointing towards
    For a newbie and looking at the physical led itself, take into account a
    newbie needs advice so explanation is done for what he actually sees and not
    by interpretation of a schematic symbol 'cause he still won't know the
    relation between the symbol and the device
  6. First of all.....thanks for all the help.
    I know to connect them in series and the resistor can go anywhere but now
    I"m confused.
    Below one person say that the shortest leg = thick side of LED = Cathode
    should be ground.
    The next person say that The *cathode* is *connected* to the moreMaybe I'm making it hard and not thinking correctly and just reading what
    the words are telling me.
    So am I correct to say that if the arrow is pointing up towards the LED and
    is on the anode side, that it is actually pointing to the Cathode side and
    down to ground. Or if the arrow is on the Cathode side it should be pointing
    down to the negative side.
    Again....thanks for all the help.
  7. peterken

    peterken Guest

    view "drawings" in notepad using fixed font

    schematic symbol (the "arrow")

    | anode (more positive side)
    \ / ->
    | cathode (more negative side)

    seen "through" the physical led
    (look at the "thick" side IN the led)

    anode | \
    =======|=====:=== \
    | __ |
    | __:/ | |
    =====|=====:___| /
    cathode |___________/

    hope this helps
  8. Helps plenty...makes more sense...... thanks
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