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president madison green display

Discussion in 'CB Radio Modifications' started by bioman, Jun 18, 2008.

  1. bioman

    bioman Active Member

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    my madison has a dead segment in the display LED so i plan to replace it with a green one to match the clock

    will i need to change the resistors on the board to be combatible with a green display since it currently has a red one in it/?

    i know the regular green 5MM LED lights want 2.2V but am not sure aboiut the displays and id hate to ruin the new one



    thanx
    scott
     
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  2. formulamojo

    formulamojo Active Member

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    I wouldn't think so. The resistors have no way of knowing what color the display is. As long as the new display is a drop in replacement for the old it should work.
     
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  3. bioman

    bioman Active Member

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    i see what you mean

    i had thought that maybe green LEDs would want a different voltage than the red ones .....

    changing the resistors to a different value would give a different voltage correct?
     
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  4. formulamojo

    formulamojo Active Member

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    Yes. A larger resistor would drop more voltage across it there for affecting the final voltage of the circuit. Not enough to be noticable unless a large change was made to the resistor.

    For example I was experimenting with my 13.8V power supply and a diode trying to dim it. when i put a 50 ohm resistor in series with the diode it only dropped the voltage going to the diode to 13.7V. A tenth of a volt wasn't noticed in my experiment, but it gave me a base line to work with. I now know that i need a 500 ohm or greater resistor to drop my voltage by 1 volt.
     
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  5. bioman

    bioman Active Member

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    ok so it shouldnt make a difference in spots where a LED already was such as on the channel display and and the lights for AM/LLSB etc.....

    i know i will need resistors where i replace the 12V bulbs behind the meters to make them light up green as well but i DO have a calculator for that so i'm good there

    i have the LEDs and the display just need to stop at rat shack on the way home to get the resistors i'll need to run 2 LEDs in series where there WAS 12V bulbs

    i'll put up pics after is done

    thanx for the help

    scott
     
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  6. formulamojo

    formulamojo Active Member

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    Have fun.
     
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  7. loosecannon

    loosecannon break on through

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    formulamojo,

    the reason that resistor in series with the power supply only dropped the voltage by .1 volts is because you did not have a load on the supply.
    that series resistor will act very differently when a load is applied.
    (resistor placed across positive and negative)
    LC
     
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  8. formulamojo

    formulamojo Active Member

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    I know, I was trying to explain voltage drop to him. To answer his question.

    They did teach me a thing or two in college where I earned a degree in electronics, :LOL: But a newbie doesn't want to be bored with theory.
     
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  9. TonyV225

    TonyV225 Supporting Member

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    I believe they sell kits for these.
     
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  10. bioman

    bioman Active Member

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    the "kit" comes with the display and one LED

    i needed the display and 4 LEDs for AM/LSB/USB/CHAN9 on the madison PLUS i wanted to put green lights on the meters

    the channel display is in and looking nice i just need to wire the LEDs for the meters and it is done but alas i leave for work momentarily
     
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  11. 74IN

    74IN Well-Known Member

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    #11
  12. bioman

    bioman Active Member

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    thanx 74 ......

    i already have a calc for the resistors and plan to pic them up at radio shack on the way home.....

    now if i could just find a clock motor for that radio.....
     
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  13. bioman

    bioman Active Member

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    ok after playing around with a bunch of resistors i had got from radio shack and some more out of my "parts" bin i just couldnt find the level of "brightness" i was looking for so i ended up tying the ground and the 15.2V sources from the original 2 lights together in parallel and ran 6LEDs in series .....PERFECT!!

    i set them up in a triangle behind each meter so ive goot a nice green glow coming off of each one

    after it gets dark ill take some pics and throw them up

    scott
     
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  14. formulamojo

    formulamojo Active Member

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    Nice.
     
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  15. bioman

    bioman Active Member

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    [​IMG]


    [​IMG]

    as promised pics of the green

    pics came out kind of crappy.... with the flash it was too bright and without was too dark and i havent really figured out how to operate this camera yet

    everything came out nice and bright with the exception of the lights behind the clock....

    IF i keep the clock in it i may end up going to white LEDs behind it since the light has to filter behind green numbers

    the clock in it does not work <needs a motor> and if i cant find a motor for it i think i'm going to tear down a freq counter and install that in the window..... a green LED one of course

    scott
     
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