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Simple flashing led questions.

Discussion in 'LEDs and Optoelectronics' started by Giggity, May 21, 2010.

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  1. Giggity


    May 21, 2010
    Hey guys. I'm new to the world of electronics and am having a hard time understanding things. I'm making a prop from Ghostbusters called Ecto goggles and I need flashing LEDs on it. I really don't want to use a 555 because I can't get my head around it. I finally found a website that tells me I can just use a resistor, a 9v battery and a flashing LED to light up a few normal LEDs. My questions is: how many LEDs can I use with this system? Can I use an on/off toggle and where would it go? Can I use some wire between the LEDs to extend them, if so, what type of wire?

    Sorry if these questions seem very simplistic but as I said - I'm very new to all this.
    Thanks for your time.
  2. eptheta


    Dec 20, 2009
    But its sooo easy to use a 555. Here's a calculator. Enter the frequency you want and put the duty cycle between 45 and 55 and it will give you the resistor values.
    NE555 Calculator

    Then just assemble this very simple circuit-->

    It can't get simpler ! (it probably can, but i do this for any timer related projects)
    Good luck
  3. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    The limit for connecting LEDs in series with a flashing LED is determined by the maximum voltage for the flashing LED and the Vf of the other LEDs at the current the flashing LED passes when "off".

    I'm sure that sounds like gobbledygook, but it serves to illustrate that the question is not trivial.

    With specs for the flashing LED and the other LEDs you are using, it could be calculated, but it depends a lot on the individual components too, so there would likely be a fairly wide spread between what was definitely safe to what was probably safe.

    It may be far easier to use the flashing LED to turn on a transistor which, in turn controls further strings of LEDs.

    But if you're going that far, it isn't much harder to use a 555 with the associated greater control over frequency and duty cycle.

    The best place is in series with the battery. It doesn't matter if it's in series with the positive or negative lead. By convention, it's usually placed in series with the positive lead.

    You would normally use insulated wire. For the current you require for LEDs, almost anything is OK. Generally, I wouldn't use something so fine that it was difficult to solder, and mechanically weak. Something with a total size of wire similar to the LED lead would be suitable. Generally you'd use multi-stranded wire.
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