A couple of simple questions regarding resistors and multimeters

Discussion in 'General Electronics Chat' started by Spgkr, May 5, 2008.

  1. Spgkr

    Thread Starter New Member

    May 5, 2008
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    0
    Hi all,

    I've no real knowledge of electronics, however i've decided i'd like to install some LED lights on my Playstation 2 (although am currently considering the modding possibilities of just about every piece of electronic equipment in my home).

    Ok, so my questions are:

    A) I used a resistor calculator online which told me (after I punched in 12 3.3v 20mA LEDs coming off a 12v supply (no idea if that's what i'll be using)) that i'd need a 1/8w, 330ohm resistor. I looked on my local electronics store website and the resistors aren't listed by wattage or by Ohm's (Well I do see Watt's but I think 10 might be overkill :p), so how can I tell? ps. The site i'm using is http://www.maplin.co.uk.

    B) How do I connect a resistor to multiple LED's? Wrap the resistor around all the positive legs and solder? (Guess, based on what i've read) But then what do I do with the negative legs?

    C) How can I use a multimeter to find a suitable component on my PS2 to solder to the resistor? I understand i'm looking for the small silver ball-like components (god i'm a newbie), but how can I tell which is negative and which is positive? And can I use any positive and negative component which is the desired wattage, or do they have to be next to each other/corrospond to each other in some way. Also, should I just measure the watts? I'd love to know how to do this so I could take apart my GBA next and put some cool stuff on it.

    And I think that's me for just now. Anyway, really sorry about the length of my questions, just want to make sure I get everything down before I get to grips with it.

    Thanks

    Jamie
     
    Last edited by a moderator: May 5, 2008
  2. Jack Bourne

    Active Member

    Apr 30, 2008
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    Ok Basically, don't try and Mod a PS2. They are beautiful machines and it will honestly just wreck it.
    The store MUST tell you the resistance and Max power consumption or else how can they sell them because they have to description.
    You dont want to be soldering the components to the PS2 power supply as there is an extremely high risk you will wreck the system.
    Use another power source. eg a 9V cuboid battery.
     
  3. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    The online calculator is wrong.
    A 12V supply and 3.3V LEDs at 20mA needs a current-limiting resistor that is 435 ohms. Use 470 ohms.
    The 330 ohm resistor will create a current in a 3.3V led of 26.4mA.

    The 330 ohm resistor will dissipate 0.23W so a 1/8W resistor will smoke and burn. Even a 1/4W resistor will be very hot.

    You should connect 3 LEDs in series. Their total voltage of 9.9V can have the current limited to 20mA by a 100 ohm resistor that dissipates hardly any heat so a resistor as small as 0.1W is fine. The current from the power supply will be 1/3rd the amount than before.
     
  4. Spgkr

    Thread Starter New Member

    May 5, 2008
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    Cheers for the quick response.

    When you say "even a 1/4w resistor will be very hot", would it be a bad idea to go with a 1/2w?

    Audioguru, I'd rather learn how to use the power supply so it turns on and off with the system.
     
  5. Wendy

    Moderator

    Mar 24, 2008
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    A better solution in general is a LM317 current regulator, or some variation. That way you feed the LEDs what you want, no major math other than designing the current regulator (which replaces the resistors with one more part) is needed.
     
  6. Spgkr

    Thread Starter New Member

    May 5, 2008
    5
    0
    Thanks Bill,

    My next question is actually just a reworded version of one in the first post: If I do want to solder the resistor to my motherboard, what is the best way to find a positive and negative component on my PS2? Can I just try different combinations with the multimeter until I get a connection? Can I use any connection my multimeter finds? Will there always be more than one possible connection?(Or in the case of a computer console).

    Thanks alot for everyones help so far btw.
     
  7. Audioguru

    New Member

    Dec 20, 2007
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    You can't power LEDs from a random voltage on a motherboard. The LED current might overload a part on the motherboard and destroy it.
    The power supply for the motherboard is not designed to drive additional things like LEDs. Use a power supply that you make or buy that is for just the LEDs.

    If a 1/4W resistor is hot then use a 1/2W resistor instead and it will operate cooler.
     
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