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Electronics How do I read blue resistors?

Discussion in 'Modding' started by disco volante, 17 Feb 2003.

  1. disco volante

    disco volante What's a Dremel?

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    Sorry if that sounds like a stupid question, but I've taken apart an ultra bright red LED cluster, since it's the cheapest way for me to get red LEDs.

    Anyways, there are 12leds, hooked up in series, to 12vdc. The input goes through two resistors in series of questionable resistence. They are about the size of normal beige resistors, except they are blue, and have an extra ring around them. For this reason, I can't figure out what the resistence value is.

    Anyways, the colors are as follows: Brown, Black, Black, Black, Red
    or maybe the other way around. Anyways, could anyone help me out with this?
     
  2. whypick1

    whypick1 The über-Pick

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    10 ohms or 20 ohms, depending on which order is correct. The bands should all be bunched to one side, which is where you start reading.
     
  3. SteveyG

    SteveyG Electromodder

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    Yes, there's usually an extra black band on the blue ones. So add ten to whichever is the multiplier.
     
  4. disco volante

    disco volante What's a Dremel?

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    Thanks for the help, everyone.

    Now, here's another question on the same subject.

    Since I now know the supply voltage (12V / 12LEDS in series would make it 1V per LED, right?), and the resistance, would it be possible to guess the current and forward voltage?

    The reason I ask is because I'd be nice to be able to run each LED of it's own resistor. But say for example I install 6 of these LEDs in a fanbus. Now, since the original amount of LEDs was 12, and there were two identical resistors, could I theoretically use 6 LEDs off one resistor, while maintaining the 12V supply? Or would I have to half that number too? (and just go for the 5 volt supply)
     
  5. whypick1

    whypick1 The über-Pick

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    Are you sure its in series? 1v for an LED is awfulllly low.

    PS. Stop being a cheap ******* and get a multimeter, it'll tell you this sort of stuff.
     
  6. cpemma

    cpemma Ecky thump

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    Sounds like there are two series strings of 6 in parallel, each with a 200R resistor. I'd assume 2v each and a forward current of 20mA won't kill them.
     
  7. disco volante

    disco volante What's a Dremel?

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    That's good to hear.

    Anyways, I just have one more question, I'd make a new thread, but I don't feel like wasting space with my stupidity.

    Anyways, I've came upon 4 ultra bright blue LEDs from radio shack. The stats are as follows

    Forward Voltage: 5.0 (6.0 max)
    Current: 30mA

    Now, I wish to run these off of the 5V rail on my power supply. According to Linear's resistor calculator, the value I aiming for is 0 ohms, which obviously means no resistor.

    I don't know if I can accept this, after having the fact that resistors are a requirement for prolonged LED life (and I'd like that, after having spent $5 PER LED). So in this case, what sort of resistor should I be using?
     
  8. whypick1

    whypick1 The über-Pick

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    You should use a really low ohm resistor of sufficient wattage (voltage being equal, lower resistance = higher wattage dissipated)

    PS. $5 a pop for blue LEDs is a ripoff. I know one place off the top of my head that you can get them for $1.50, there are probably some that other BTers know that stock 'em for less than a buck.
     
  9. disco volante

    disco volante What's a Dremel?

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    Yep. The problem is that the fact that Radio Shack has a monopoly over electronics parts in my small town. The other problem is the Canadian currency I have to pay with. The final problem is that I can't really order online because I don't have a credit card, and I'm impatient.
     
  10. cpemma

    cpemma Ecky thump

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    One answer is to pretend they're 4v leds and use a 33R resistor with the 5v line. They should light fine but may not be as bright as they could go with the better solution, a 240R resistor on the 12v line. But it won't bork them. ;)

    I looked for 5-6v leds on the Kingbright site without success a few weeks back, so I've never seen a datasheet. All the Kingbright blues are the usual 3.5-4v.
     
  11. Digitalblueshift

    Digitalblueshift What's a Dremel?

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    Ok, I'm sorry but ive flown past this thread six times in the past two days and resisted the urge for long enough.

    How do you read the blue resistors?

    [sarcasm]
    The same way to read any other type of resistor!
    [/sarcasm]

    Each colour band means a number or a multiplier or a variance, Im sure youve gotten to that by now, I dont exactly know which coloriswhich,but they areallaround the internet.
     
  12. cpemma

    cpemma Ecky thump

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    It's a bit more complex than you suggest these days, with at least 3 banding systems on the go. That red band on one end could be 2% tolerance, 50ppm temperature coefficient, or a 2. The brown band on the other end could be 1% tolerance or a 1.

    Just to be awkward, Maplin 1% resistors have five bands but use the 4-band value system.

    I cheat and use the multimeter. ;)
     
  13. whypick1

    whypick1 The über-Pick

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    That's not cheating, that's the good way to do it! Cheating would be pumping juice into it and seeing how much you need to put into it before it blows up.
     
  14. JazzXP

    JazzXP Eh! Steve

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    No, that's not cheating... that fun :lol:
     

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