555 timer help - high & low leds

Discussion in 'The Projects Forum' started by spacefighter, Mar 13, 2011.

  1. spacefighter

    Thread Starter New Member

    Mar 12, 2011
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    Hi ,
    I am trying to build a 555 timer from a project I found on the web. ( http://poweredpowerhour.wordpress.com/ ) pretty cool huh . For his build he has a 555 timer that’s high for 55 sec and low for 10 sec. I have been able to do the same but I would like to change it up a bit. I want to have one led light up for the 55 seconds and then switch to a different color for the 10 seconds. I don’t really know anything about 555 timers and my knowledge is still very basic but what I came up with was to use a PNP transistor to power the different led when the timer is low. I don’t even know if this is the right thing to do but I sounds about right. Anyways I hooked everything up and no luck. The 555 timer just gets really hot to the touch after a short time. Anyone have an idea of what’s wrong. Or if I am even doing it right ha. Here is a picture of what I have tried, sorry I didn’t put a lot of time into drawing it.
    Thanks!
     
  2. Wendy

    Moderator

    Mar 24, 2008
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  3. spacefighter

    Thread Starter New Member

    Mar 12, 2011
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    Thanks for the reply!
    I'll give it a try but I am a little confused about the resistors. To get the timing I want 55 seconds for one led and 10 for the other. Which resistors would I replace? Are the resistors that are connected to the leds just to protect from the 9 volts or do they deal with the timing?
     
  4. Wendy

    Moderator

    Mar 24, 2008
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    First, pick the circuit you are talking about.

    This is a Hysteretic oscillator...

    [​IMG]

    555 Hysteretic Oscillator

    It only has two components besides the 555. It doesn't have to be a 555, it will work with any inverting Schmitt Trigger. The theory of the oscillator is explained in detail in the article. All the other parts are for the LEDs.

    LEDs, 555s, Flashers, and Light Chasers - Chapter 4, The 555 Integrated Circuit

    This explains why the LEDs act like they do.

    OK, for precision timing like you want, you can use this circuit...

    My Cookbook

    [​IMG]

    or this...

    [​IMG]

    This one is probably easier to make.
     
    Last edited: Mar 13, 2011
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  5. spacefighter

    Thread Starter New Member

    Mar 12, 2011
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    Hey Bill,
    Thanks soo Much for all the help! It took me a little bit to understand what was happening and why/how. Just finished my project, inspired by this ( http://poweredpowerhour.wordpress.com/ ) , now what’s left is to impress the friends :)
     
  6. Wendy

    Moderator

    Mar 24, 2008
    20,764
    2,535
    Not bad. Pretty good as a matter of fact.
     
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