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What resistors do I need for LEDs? + IC question

Discussion in 'LEDs and Optoelectronics' started by Satch, Dec 17, 2012.

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  1. Satch

    Satch

    6
    0
    Nov 15, 2012
    I want to do some projects with Arduino and I plan on buying one soon so I'm just sourcing components to work with.
    I want to get these (It's way more than I need, but the price is good and I'll always have plenty of them) http://www.ebay.com/itm/2000-pcs-As...777?pt=LH_DefaultDomain_0&hash=item1c2e68c679 but I'm confused by all the different types of resistors - 1W, 1/2W, Mylar, metal film, carbon film etc.
    So can anyone tell me what kind of resistors I need for these LEDs? http://www.ebay.com/itm/220988641549?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1438.l2649
    (Scroll down to see specs and info on them)

    Also, is it necessary to have an IC socket to use an IC? The ones I've seen don't seem to come with sockets?

    EDIT: forgot to mention, the Arduino will be powered by a 9V battery, which if I understand correctly, Arduino changes that to 5V.
     
    Last edited: Dec 17, 2012
  2. CocaCola

    CocaCola

    3,635
    5
    Apr 7, 2012
    See Steve's sticky on LEDs and then come back with any particular questions...

    For the LEDs you are using 1/8 or 1/4 watt resistors will be plenty fine, as for what kind that doesn't matter they all do the same thing, some just hold better tolerances and that isn't all that important in your application... Carbon film will likely be the lowest cost, but sometimes some great deals can be had on metal film ones one Ebay, that generally hold better tolerances...

    No IC sockets are not necessary but they do make it easier to service and for many newbies I would advise their use if you are soldering the IC to a PC board...
     
  3. Satch

    Satch

    6
    0
    Nov 15, 2012
    Thanks for the answer, there's a lot of information to get my head around in that thread and I'll have to re-read it and watch a few videos to properly understand all that.
    Is it correct to say that if I had a power supply of 5V, when it passes through an LED with foward voltage of 3, the volts drops down to 2V anywhere in the circuit AFTER that LED? So therefore the next LED in the sequence would be dimmer? (unless wired parallel?)
    Sorry for the nooby questions
     
  4. CocaCola

    CocaCola

    3,635
    5
    Apr 7, 2012
    To keep is simple...

    The short of it yes, I have seen LEDs used to level shift in a pinch but IMO it's not a good long term solution or one you should use as LEDs need their current limited or else they will pop, you need something in series that will limit current or use up all excess voltage unless current is fixed by the supply... But, even then if something is using the excess voltage you could have thermal run away...

    You do exploit this voltage drop when doing series/parallel LED configurations and calculations though...

    Chances are neither would light because the circuit would not be complete as the 2nd LED will not get enough forward voltage to complete the circuit...
     
  5. Relayer

    Relayer

    39
    0
    Dec 15, 2012
    The prices of those LEDs are quite reasonable and are worth getting.
    In all cases if you're only going to use one LED at a time, then 1/4 Watt resistors will suffice.
    If you plan on stringing them together, then you either need to go higher in Wattage or provide a dropping resistor for each.
    Since you are going to be using the Arduino's 5 volts, then you should be configuring your LEDs in parallel if you're going to use two or more. Reason being if they were to be mounted in series, each LED requires a voltage drop across it.
    If you're going to use one LED at a time, then one standard value resistor will only be required in all cases regardless of the LED type and color.
    So in your case, using the 5 volts provided by the Arduino's power supply, you can use a 150 ohm resistor comfortably with all the listed LEDs.
    I hope the above gives you a little bit more of an insight.
    Regards,
    Relayer :D
     
  6. CocaCola

    CocaCola

    3,635
    5
    Apr 7, 2012
    Performance of the Green, Blue and White will be below average with a 150 Ohm resistor, 100 Ohm is better suited for those colors...
     
  7. Relayer

    Relayer

    39
    0
    Dec 15, 2012
    That's fine if you want to burn out your retina :p They are 4000+ mcd LEDs.
    I feel that 150 ohm is quite adequate, in fact you could probably use a higher value resistor as looking at the LEDs straight on can glare quite badly.
    Regards,
    Relayer :D
     
  8. CocaCola

    CocaCola

    3,635
    5
    Apr 7, 2012
    So? It all depends on your desired application... 4000 is bright if you look directly at it from a close distance, but it's not that bright in many other applications if not directly viewed straight on with nothing in front of it or from a distance...

    Again it all depends on application, as for asequate the red, yellow and orange are all 4000+ mcd yet you suggested running that at at 150 Ohms, kinda negating why you suggest running the blue differently if it was about brightness levels...The white and green are higher values but from my experience mcd ratings are pretty much useless when you get to those levels as they are measured at the perfect point of focus so they can brag about how bright they are, 1 degree off from dead on and many drop off in mcd rating significantly...

    IMO, best to show the student how the calculate the values vs just saying use this without explanation...
     
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