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bi-colour transistor circuit

Discussion in 'General Electronics Discussion' started by qweets, May 16, 2012.

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  1. qweets

    qweets

    48
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    Sep 26, 2010
    hi, i made this bi led circuit below so that an arduino with 2 pins can change a single led
    from red to green and off.

    allthough it works great. I think my resistor values are a too low and may harm the transistors over time, yet when i raise the values the bi-led becomes duller.

    here below is the circuit runing from a 5v regulated circuit ,
    led spec:
    Maximum Forward Current 25/30mA
    Maximum Forward Voltage per Colour 2.5V

    i wonder do these resistor values look o.k?

    one objective was to make a small footprint.

    Thanks for your help : )

    [​IMG]
     
    Last edited by a moderator: May 16, 2012
  2. qweets

    qweets

    48
    0
    Sep 26, 2010
    topic closed ,

    I had a question here regarding a circuit but found out the problem was simply that a rogue transistor found its way into my 2n3904 bag. luckly i had my magnifying glass close at hand.
    : )
     
  3. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,491
    2,833
    Jan 21, 2010
    It seems overly complex.

    Just having the 2 pins driving individual transistors that switch a diode on and off would appear to be essentially equivalent as long as you're controlling the uC and you're not converting some particular bit pattern to the LED behaviour in a non-trivial way.

    I'm not sure what the bottom transistors are supposed to do. They seem to turn on in parallel with a LED in a way that simply wastes power.

    edit: if it's a red/greed led, there are also easier ways to do this. Another problem is that you can never have both on at the same time (that may be a feature you want though)
     
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