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Thread: LEDs too dim?

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    150+ Forum Groupie HondaCop's Avatar
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    LEDs too dim?

    Hello all,

    I think my MIP annunciator LEDs are too dim. For each annunciator, I have used (2) 5mm LEDs in series with no resistors. The anode of the pair is connected to the ground on my OpenCockpits USB Expansion card outputs ground and the cathode is then connected to the corresponding output connection on said expansion card.

    All LEDs are 5mm and 5 volts.

    Why would they be dim? I don't think these were labeled as high intensity LEDs when I purchased them.

    So I need to replace them all with High Intensity LEDs? Or can I do something to these in order to make them brighter?
    Regards,

    Efrain "E" Ruiz (HondaCop)
    LiveDISPATCH @ http://www.livedispatch.org

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    1000+ Poster - Fantastic Contributor Bob Reed's Avatar
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    Re: LEDs too dim?

    If you are feeding these 5 volts and they are 5 volt LEDs you should not be running the in series but in parallel. By running them on series you are dropping the voltage to them
    Bob Reed

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    Re: LEDs too dim?

    And - if you do not use a current limiting resistor then they will probably go pop!

    By all means wire the leds in parallel BUT use a current limiting resistor of say 222ohms and then check the brightness and how much current you are drawing. Subject to the OC cards limit of around 20ma per output try reducing the values of the rsistors. I have found that you need high intensity leds to effectively light the annunciators and also ones with a wide field of view - else you just get bright spots

    David

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    25+ Posting Member shafian's Avatar
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    Re: LEDs too dim?

    hondacop.. what do you mean by grounding it on the USB card? AS far as i know each Master card has its own outputs ground.. Not sure if that would make a difference as i was under the impression thats how you wire it up.

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    Re: LEDs too dim?

    Quote Originally Posted by Bob Reed View Post
    If you are feeding these 5 volts and they are 5 volt LEDs you should not be running the in series but in parallel. By running them on series you are dropping the voltage to them
    Quote Originally Posted by fordgt40 View Post
    And - if you do not use a current limiting resistor then they will probably go pop!

    By all means wire the leds in parallel BUT use a current limiting resistor of say 222ohms and then check the brightness and how much current you are drawing. Subject to the OC cards limit of around 20ma per output try reducing the values of the rsistors. I have found that you need high intensity leds to effectively light the annunciators and also ones with a wide field of view - else you just get bright spots

    David
    Ok, so in other words, I should wire them in parallel and use a 470 ohm resistor on the cathode?
    Regards,

    Efrain "E" Ruiz (HondaCop)
    LiveDISPATCH @ http://www.livedispatch.org

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    Re: LEDs too dim?

    Hondacop

    You only need to use one resistor as it is the current to both leds that you are limiting. By all means start at 470 ohms to be safe and then reduce down to see what happens to the light level versus current drain

    If you buy high intensity leds then you can always reduce brightness by one means or another but not increase it! I use 5000mcd leds from Hong Kong, cheaply available on Ebay. Also make sure that you get the widest viewing angle that you can

    Regards

    David

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    Re: LEDs too dim?

    Quote Originally Posted by fordgt40 View Post
    Hondacop

    You only need to use one resistor as it is the current to both leds that you are limiting. By all means start at 470 ohms to be safe and then reduce down to see what happens to the light level versus current drain

    If you buy high intensity leds then you can always reduce brightness by one means or another but not increase it! I use 5000mcd leds from Hong Kong, cheaply available on Ebay. Also make sure that you get the widest viewing angle that you can

    Regards

    David
    Hi David,

    Would these leds get the job done quite nicely?

    RED

    YELLOW/AMBER

    GREEN
    Regards,

    Efrain "E" Ruiz (HondaCop)
    LiveDISPATCH @ http://www.livedispatch.org

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    Re: LEDs too dim?

    Efrain

    They seem ok, with a current drain of 24/25ma. I had not seen these flat top ones before, but one point to watch is that I believe the light output in mcd`s is also a function of the angle of view, so that a very wide angle will spread less light over a greater area.

    I have hundreds of leds bought in error!! I would advise that you order some 12000mcd ones and try them out, it might be that one 12000 mcd wide angle led might do the trick. It all really depends on the light output, angle of view, distance from the annunciator lens and current. I would strongly suggest you trial it first before buying too much, as I did!!

    I am going to order some 12000 mcd and see if they will do the business for my overhead on the basis of only one led per annunciator.

    Regards

    David

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    Re: LEDs too dim?

    Keep in mind that there are also "5-volt" LEDs out there.... that is LEDs with the current limit resistors built into the LED. You would not need to use an external resistor with those.

    Also the earlier post regarding the OC mastercard is correct. If you are using J2 then GROUND is on PIN # 2. If you are using P2 (DB9) then the GROUND is again on PIN # 2. I am unsure if the USB expansion card shares a common outputs ground with the mastercard, so prob best to use the ground supplied on the connector.

    Not related to your post, but keep in mind that each group of inputs on the mastercard has it's own group ground.

    BuddyM

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    Re: LEDs too dim?

    Just to clarify, I HAVE connected all my LEDs to the OUTPUTS connector which like many have said, the #2 pin is the ground. All my LEDs use this common ground and each OUTPUT is used to power a PAIR of LEDs in series with NO resistor.

    I guess the LEDs I am using are just too dim and I need to buy LEDs with a much higher MCD value.
    Regards,

    Efrain "E" Ruiz (HondaCop)
    LiveDISPATCH @ http://www.livedispatch.org

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