how do i use a 555 to alternate leds

Discussion in 'General Electronics Chat' started by griffin175, Jul 14, 2014.

  1. griffin175

    Thread Starter New Member

    Jul 14, 2014
    sorry if im doing this wrong, im new to forum sites.

    first i tried using a youtube video tutorial but only one led was lit, when i change the resistance, the leds switched once. if resistance was above one point one would light, if it were below the other would light. is this something the 555 can do by design or did i invent a new use(probably not).
    anyway, i kinda fixed it, but how can i be sure both have the same on time and the same off time? i know the resistor value effects that, should i just use the same value resistor for the #2 #7 pin and the + #7 pin?
    after i get that equal time sorted out, i would be able to change the speed of the switching with one potentiometer, is that possible?
    i would also like to change the brightness with one other potentiometer.

    i would give you the schematic of my circuit but its probably so bad it would be easier to start over. i am pretty new at this, dont be mean.
  2. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
    People here aren't mean. Occasionally we may tease, but in an educational manner.

    Please show us your schematic, so we can understand what you've tried.

    Here's how to add an attachment
  3. inwo

    Well-Known Member

    Nov 7, 2013
    Are you using something like this? From google!
  4. wayneh


    Sep 9, 2010
    If you just need "close", it's easy. But if you need a precise 50% duty cycle, you may need another strategy. There was a thread in this forum not long ago about achieving 50% duty cycle with a 555 timer.

    The brightness of either LED can be changed by a pot in series with it, but you'll also want a fixed resistor to limit the current to the maximum brightness assuming the pot is at zero ohms. Otherwise, it will always happen that someone will turn that pot all the way to one end and blow the LED.
  5. griffin175

    Thread Starter New Member

    Jul 14, 2014
    inwo, that is the schematic i used only the resistors on the 555 are both 1k and my capacitor is 220uF, it seems to be close to 50% but its a little bit off. as long as it is between %45 and %55 duty cycle that would probably not be visually noticeable. is there a way to do that? i would also like to change the frequency with a potentiometer.
  6. BobTPH

    Active Member

    Jun 5, 2013
    To get a 50% duty cycle. Eliminate R1 and connect the top of R2 to pin 3, leaving pin 7 unconnected. This is a cool trick that uses the same resistor to both charge and discharge, making the duty cycle always 50%.

  7. inwo

    Well-Known Member

    Nov 7, 2013