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  1. #1
    Frugalphile Howlindawg's Avatar
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    Indicator LED: Will this be too bright?

    Looking to add a power on LED to the front panel of my DAC enclosure.

    I can source 3mm blue LEDs locally with the following specs.
    Intensity 180mcd
    Forward current 20mA
    Forward voltage 3.7V
    Viewing angle 40 Deg
    Lens: Diffused, uncoloured.

    Power supply is 11.6V so I was going to use a 470 Ohm 1/2 watt series resistor.

    The thing is that I have no idea of how bright this LED will actually be in real world use.
    The last thing I want is a retina scortching laser beam sitting in the equipment rack hence the choice of a diffused lens.

    Anyone experienced care to sanity check my choice of LED and resistor value please?
    The truth may be out there, but the lies are inside your head.

  2. #2
    Super Wammer
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    Are they from Maplins? I used a maplins blue LED in my power amp, and it was very, very bright (although I can't remember the spec). The resistor is used to limit the current through the LED. 470 Ohm's should be about right. Any lower and you'll limit the life of the LED. The intensity of your LED is 180mcd, which will be very bright. Standard LED's (red, green & yellow) are normally around 30-40mcd.
    Tomorrow belongs to those who can see it coming.
    Chris.

  3. #3
    Frugalphile Howlindawg's Avatar
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    Quote Originally Posted by zebra100 View Post
    The intensity of your LED is 180mcd, which will be very bright.
    Thx, that's what I was afraid of.
    All I want is a glow so I'll keep looking for a less intense version.
    The truth may be out there, but the lies are inside your head.

  4. #4
    Registered sirius's Avatar
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    If you purchase some higher value resistors you will be able to experiment to find the right level of brightness. I have done this with three amps so far and the led's are still working fine at a non-intrusive light level.
    Hope this helps.

  5. #5
    Frugalphile Howlindawg's Avatar
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    Would it make sense to use a trimmer instead of a fixed resistor and use that to adjust the intensity?
    The truth may be out there, but the lies are inside your head.

  6. #6
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    Quote Originally Posted by Howlindawg View Post
    Would it make sense to use a trimmer instead of a fixed resistor and use that to adjust the intensity?
    Hi, Yes, if your going to be that particular about it. Otherwise simply don't run it at full current. rgds, sreten.
    Last edited by sreten; 22-06-2011 at 10:23 AM.

  7. #7
    Cogito, ergo doleo. rabski's Avatar
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    If you can put up with green, pm me your address Martin. I've got a pile of panel mount (nice silver bezel) ones that are designed for 12v with built-in resistors so I'll post you one.
    I know that you believe you understand what you think I said, but Iím not sure you realise that what you heard is not what I meant.

  8. #8
    Wammer adsa's Avatar
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    Also note that some LED's are noisy!! I changed one in an amp once, as the previous was intermittent (broken leg). The new one made a slight fizzing noise through the speakers when replaced. This was a blue LED.
    845 SET's ROCK!!!

  9. #9
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    Led indicators have a life of at least ten years and consume 90 per cent less power than conventional indicators. Indicators have almost these are available with in-built legends, ie, standard legends available r, y & b for phase indication and on & off, led flashers and led buzzer flashers.Led buzzer flashers have the dual ability of flashing and giving an audio output from a single unit. led replacement

  10. #10
    Super Wammer
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    Hi,

    unfortunately the trimmer idea maybe a non-starter, as most trimmers (Variable Resistors) will not handle the power. To calculate power, you can use either Volts x Amps = Watts or V(squared) divided by Resistance. Whilst I agree blue leds look "cool" in a lot of equipment they are far too bright. I recently attended a conference where the presenter was using a PA system and Mixer, which was full of blue leds, and it was facing towards the audience, after a short while, I had to ask the presenter to cover the amps & mixer with some papers, since a few of us in the audience were being blinded by the blue leds. I have also found that blue leds dont dim very well, with the old red leds you could change the restance/current and still get a red glow, but with blue it seems to be all or nothing.

  11. #11
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    Just mount it a few mm behind its hole, that'll dim the crap out of it

  12. #12
    Super Wammer Cable Monkey's Avatar
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    Quote Originally Posted by Radioham View Post
    Hi,

    unfortunately the trimmer idea maybe a non-starter, as most trimmers (Variable Resistors) will not handle the power. To calculate power, you can use either Volts x Amps = Watts or V(squared) divided by Resistance. Whilst I agree blue leds look "cool" in a lot of equipment they are far too bright. I recently attended a conference where the presenter was using a PA system and Mixer, which was full of blue leds, and it was facing towards the audience, after a short while, I had to ask the presenter to cover the amps & mixer with some papers, since a few of us in the audience were being blinded by the blue leds. I have also found that blue leds dont dim very well, with the old red leds you could change the restance/current and still get a red glow, but with blue it seems to be all or nothing.
    Actually the trimmer idea is probably the best because you don't leave it in! You adjust it to a level which suits you, measure it and find a resistor of similar value. It really isn't hard to adjust their brightness and even change them for a colour you prefer in many cases. Making them duller has no impact on their reliability and the blue ones I have put in I have been able to adjust them so they are ok for me.
    Let me get this straight. You take a perfectly good CD and put it in a DVD player??!!

  13. #13
    Super Wammer
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    Or alternatively, a few turns of insulated copper wire (same as used in inductor coils) wrapped round the coil of your transformer (I'm assuming torroidal). Atatch the LED to the ends using fly leads. You can adjust the number of turns to give you the desired intensity. You won't have to wory about polarity with it being AC.
    Tomorrow belongs to those who can see it coming.
    Chris.

  14. #14
    Frugalphile Howlindawg's Avatar
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    Sheesh, this post was months old.

    Quote Originally Posted by Cable Monkey View Post
    Actually the trimmer idea is probably the best because you don't leave it in! You adjust it to a level which suits you, measure it and find a resistor of similar value.
    Yup, this is what I ended up doing and it worked a treat.
    Temporarily fitted the trimmer, adjusted to taste, measured the resistance and bought an appropriate resistor for permanant use.
    The truth may be out there, but the lies are inside your head.

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