Cant get it to work


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  1. #9
    Join Date
    May 2008
    Location
    Italy
    Posts
    825


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    I guess its possible that I have a bunch of bad chips
    Expecially if you have powered them with reverse supply.

    You show 1K resistor in series with leds. This is too much!

    Let's make the resistor calculation together:
    It is safe enough to assume 1.7 voltage drop for non-high-brightness red led, so 5 volts - 1.7 volts (led drop) = 3.3 volts

    10 miliamps is the normal forward current for a standard led so:

    3.3/0.01 = 330 Ohms

    With 1K you will have a very weak led since: 3.3/1000= 0.00333 = 3.3 milliAmps
    just 1/3 of the current required.

    Al.
    Last edited by aratti; - 7th April 2010 at 23:46.
    All progress began with an idea

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