Need Help with a Project Please!!

Discussion in 'The Projects Forum' started by DavidPatterson, Jun 6, 2007.

  1. DavidPatterson

    Thread Starter New Member

    Jun 6, 2007
    2
    0
    Hi there First time post can anyone help me with my project please!!

    Im trying to build a Led circuit for a model ship in total there is 16 Led's

    11 of them have a Vf of 4V @ 20mA
    5 of them have a Vf of 2.5 @ 20mA

    With a 9V Dc power supply and a switch.

    Can anyone tell me how I would go about connecting them in and with what resistors.
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Please see the E-book section here - http://www.allaboutcircuits.com/vol_3/chpt_3/10.html - for the explanation of LED's & limiting resistors.

    If you are wishing to use a 9 volt battery, it may prove a frustration. Their discharge curve is pretty poor with a 15 ma draw. If the LED's need to be on for more than a couple of minutes, consider using a wall transformer.
     
  3. cumesoftware

    Senior Member

    Apr 27, 2007
    1,330
    10
    Use the formula:
    Rlimit = (Vsupply - Vled) / Iled
     
  4. DavidPatterson

    Thread Starter New Member

    Jun 6, 2007
    2
    0
    Thanks was able to work it out. thanks for the link to the refrence files been a great help. Im off to try it out now. Thanks again.
     
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