Results 1 to 3 of 3
  1. #1
    1000+ Poster - Fantastic Contributor Jackpilot's Avatar
    Join Date
    Dec 2005
    Location
    MONTREAL
    Posts
    1,046
    Contribute If you enjoy reading the
    content here, click the below
    image to support MyCockpit site.
    Click Here To Contribute To Our Site

    LEDs in Annunciators

    1) Is there any way I can chek the proper voltage to be applied to a specific LED
    Reason: I have bags of bulk LEDS without any spec sheet.
    Or should I assume that yellow are 2.1V red 2,3V blue 3.5V ??

    2) I found too that connecting 2 Yellows in series in each Annunciator could avoid the resistor and simplify things as my supply voltage is 5V across the whole system. But this would give 2.5v for each yellow LED. Would they fry after a while if they are the 2,1V type,or will they hack it?
    Thanks for info
    Jack
    Jackpilot
    B737-700 Posky
    FS9/P.Magenta
    without PMSystem

  2. #2
    2000+ Poster - Never Leaves the Sim Trevor Hale's Avatar
    Join Date
    Nov 2005
    Location
    Ontario, Canada
    Posts
    2,432
    Contribute If you enjoy reading the
    content here, click the below
    image to support MyCockpit site.
    Click Here To Contribute To Our Site

    Hey Jack...

    Anyone will always tell you to use a resistor always with an LED. I must say that I in the past have many times not followed this rule, however the proper way to control current going to the led is with a resistor.

    That being said.. if you can regulate it properly without fluctuation most led's can tolerate under 3V. In order to maintain uniform briteness I suggest using resistors with all your led's regardless the voltage. 5V and a 330 Ohm resistor will keep you safe.

    Trev
    ________________________
    Trevor Hale

  3. #3
    Heli Builder fweinrebe's Avatar
    Join Date
    May 2008
    Location
    Namibia
    Posts
    325
    Contribute If you enjoy reading the
    content here, click the below
    image to support MyCockpit site.
    Click Here To Contribute To Our Site

    The resistor is there to limit the current through the LED, otherwise it will pop. Not using a resistor means that you have no control over the current flowing through the LED(s). Not recommended.

    To find out what the voltage is (without a Datasheet) use the following method:

    1) Use a voltage such as 5V or 12V which is easily obtained by a computer PSU.

    2) Put a 10K (> 10K should also work) potentiometer in series with the led and set it to the maximum resistance before applying power.

    3) Apply the power and slowly turn the potentiometer (variable resistor) until the LED is illuminated with the brightness you think is the maximum. (If it popped you went too far)

    4) Take a voltmeter and measure the voltage over the LED. That is the voltage used by the LED (LED Voltage drop).

    5) Power off and measure the resistance set on the potentiometer. That can be used to determine which resistor can be used with the LED and what the current is that the LED uses.

    The formulae for the resistor is:

    R = (Vcc - Vled) / I

    Most LED voltages ranges between 1.5V and 3.3V. I normally use 20mA as a ball park figure for LED current. I wired Infra-red LEDs the other day that were rated at 100mA and 1.5V.

    [Edit] See Mike Powell LED dimmer page: http://www.mikesflightdeck.com/led_dimmer.htm
    Last edited by fweinrebe; 01-06-2009 at 07:26 AM. Reason: Added link
    Fritz -> Helicopter Cockpit Builder
    (FSX | TH2Go | Arduino | C# Avionics | CNC)

  4. Thanks Jackpilot, Michael Carter, Kennair thanked for this post

Similar Threads

  1. BU0836X and LEDS
    By NCW in forum Westozy's Mechanical Engineering
    Replies: 6
    Last Post: 08-18-2011, 06:28 AM
  2. Leds
    By B763 in forum General Builder Questions All Aircraft Types
    Replies: 2
    Last Post: 06-30-2010, 07:22 PM
  3. LEDs too dim?
    By HondaCop in forum General Builder Questions All Aircraft Types
    Replies: 18
    Last Post: 09-10-2009, 08:26 AM
  4. Overhead LEDs
    By RalphW in forum Where to Start Building a Home Cockpit
    Replies: 0
    Last Post: 07-03-2007, 07:46 PM