very basic LED question

Discussion in 'General Electronics Chat' started by luca l, Jan 12, 2005.

  1. luca l

    Thread Starter New Member

    Jan 12, 2005
    2
    0
    Hi,

    Its been a long while since I've done any electronics (always at a pretty basic level), and I need to do a very simple project but am having trouble getting back into it. Wondering if someone could give me a little push in the right direction...

    I need to build a circuit that will make 3 LEDs fade and get brighter (analog style) synchronously in a loop, and when a switch is triggered, the LEDs will blink on and off asynchronously in a seemingly (but not necessarily a true) 'random' fashion.

    The only catch is that I need the circuit to be as small as possible (thankfully I sort of remember how to print up a circuit!) and inexpensive as possible as I'll be making lots of them. Related to this - is it possible to use a small, watch-style battery to power these LEDs?

    Sorry if this is too basic - like I said, its been a very long while and I never really understood what I was doing with electronics anyway. :)

    Thanks so much,
    Luca
     
  2. mozikluv

    AAC Fanatic!

    Jan 22, 2004
    1,437
    1
    hi

    for your blinking LEDs you can use the 555 timer and have it operate at astable mode and for your fading LEDs you can use either transistor driven or a quad op-amp.

    since you want to supply it with button cells you have to take into consideration the forward voltage of the LEDs you want to use. each color has different Vf and they range from 1.2v to 2.4v. if it's a flashing LED it would have a Vf of 9v to 12v. likewise the op-amp supply voltage. :)
     
  3. seaspac

    New Member

    Jan 13, 2005
    1
    0
    hi ,
    Is the sequence in first phase before triggering the switch is important ?? means LEDs should fade and bright in synchronous sequence like all fade then get bright one by one , or u need a random sequence fade and bright ??

    may be clearing your question help me think a solution to ur problem
     
  4. luca l

    Thread Starter New Member

    Jan 12, 2005
    2
    0
    Hi there,

    The LEDs must first fade and bright all together at a steady interval, but after the switch they must blink one by one in a "random" sequence. Does that clarify what I mean?

    Thanks for the other response too... I'll look into those things.
     
  5. mozikluv

    AAC Fanatic!

    Jan 22, 2004
    1,437
    1
    hi

    as soon as the switch is close the quad op-amp will do the fading of the LEDs, as it fades out at a certain ground potential level it will trigger the 555 timer operating in astable mode to do the blinking.

    what has to be resolved is how long or how many times will your LEDs light & fade before the blinking takes over. since you will be using the same sets of LEDs to do 2 different function, the light/fade circuit has to be isolated from the blinking circuit. i was thinking of the johnson decade counter as a go between but am not sure just yet.

    maybe "seaspac" has a better idea or some other members :)
     
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