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Thread: Bulgin LED Switch help

  1. #1
    Constant Bitrate
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    Bulgin LED Switch help

    I bought the following switch thinking that it would be an easy install, and it wasnt.

    http://www.frozencpu.com/ele-70.html

    the site says that I would need a 560 Ohm resistor(Which I have), and that should take the 5V that is coming off of my computer mobo and take it doen to 3.3V which the LED switch likes. Well I take a reading using a DVM before hand making sure it is 5V(4.99-5.00V to be exact), and I take a reading after I test fit the resistor(no change in voltage with it installed either way on the Positive side). My question to you guys is, what am I doing wrong? I should see a change reguardless right?

    Please help.

  2. #2
    Newbie STIdev's Avatar
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    The resistor controls the current. The current will only flow one way through the LED. If its connected backwards the LED will not light up, current will not flow through it and hence the voltage read at the LED will still be nearlly the same as the input voltage. If you reverse the positive and negative to the LED I suspect this will solve your problem. Having had it wired backwards won't damage the LED.
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  3. #3
    Constant Bitrate
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    I tried that and the same thing happened. I also took a reading fom the end onf the resistor and it was stil at 5V.

  4. #4
    Maximum Bitrate Danceheaven's Avatar
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    Its ok mate dont worry about the voltage, the resistor just controls current, as long as the current is limited to about 20 mA the voltage wont matter the led will self regulate to 3.3b, fit the resistor then measure across it with a meter and you should see 3.3v or there abouts
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  5. #5
    Newbie STIdev's Avatar
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    Which color did you get?
    For Blue the forward Voltage should be 3.6VDC and about 60mA which with 5VDC input you should use a 23 Ohm resistor and for 12VDC input use a 140 Ohm resistor. Now that would be to run it at 60mA. If you want to have it dimmer then to run it at 20mA with a 5V source use a 70 Ohm resistor. So I think your resistor is just to large.
    I hope this helps. I have one of these and run the LED from the 12V and because it can go as high as 14.5 (un regulated) I use a 210 Ohm resistor. (I also don't want it too bright)
    2004 Subaru STI
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    WinXP Pro, ME 2.1, AudioBahn 5100T Amp
    AWT10X Sub, JL XR100-CT tweeters
    Sony XPlod fronts, Kenwood Excelon rears

  6. #6
    Constant Bitrate
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    ok well the switch doesnt lightup with or without the resistor. I go tthe blue one and according to frozenCPU I needed a 560 Ohm, but if I need a nother one I will try that. Thanks.

  7. #7
    Variable Bitrate 84RegalRider's Avatar
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    probably killed the led. Also u would need the led working to see what the voltage is at the led, because if it is not in or dead. it would read whatever the source voltage is which in this case is 5volts.

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