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Alternating led flasher 555 timer?

Discussion in 'LEDs and Optoelectronics' started by Codyf1113, Aug 21, 2013.

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  1. Codyf1113

    Codyf1113

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    Jun 18, 2013
    Im trying make a blue dash light for my truck out of 6/8x 1w leds. But I like start out with something small first before I try and make it. I made one led with 555 timer flash. I now want try make two leds flash not together but back/forth between each other. I came across few videos about doing it but no schematics for them. I drew these up but I'm not 100% sure they are right..Before I try and make this circuit could someone please take look at the schematics I drew, and give me their opinion on it? I would really appreciate it.

    Only problem I see is for R1 and R1 resistor
     

    Attached Files:

  2. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    Sorry, your circuit is flawed.
    LED1 will never light up because its cathode is connected to Vcc, i.e. backwards.
    LED2 will not light because it is connected from output to threshold.

    Have a look at this schematic. Just leave out the photocouplers IC2 and IC3.

    To power your number of 1W LEDs you will need a driver circuit. Read the tutorial on LEDs.
     
  3. Codyf1113

    Codyf1113

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    Jun 18, 2013
    I love when they make schematics like that, Really messes up my mind when they mix thing up and move the numbers of the pins around. One of the best videos I've found was this one and it was main one I went off of What you said and rematching video few times is it right now?
     

    Attached Files:

    Last edited: Aug 21, 2013
  4. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    ICs are commonly drawn with the pins grouped or ordered by function, not by physical pinout of the chip. Normally, that makes reading a schematic easier (and independent from the physical layout which may differ for variants of the chip's housing).
    The schematic I linked is a particularly bad example because it reorders the pins without an obvious advantage. You got it right anyway. Just add that 100nF capacitor from pin 5 to GND for better stanility.
     
  5. Codyf1113

    Codyf1113

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    Jun 18, 2013
    Thanks for the help : ) But do have one more question still and that's the resistors I need for R1 and R2 to the leds. How can I tell how much power is coming from pin 3 So I can find the resistor I need?
     
  6. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    First of all: an LED is current controlled, not voltage controlled. Read the tutorial in the tutorial section to get acquainted with LEDs.

    Assume pin 3 to be either 0V or 9V. Either way, the voltage drop across R1+LED1 or R2+LED2 will be approximately 9V. From that subtract the LEDs voltage at the current it is designed for. For example, a red LED could have 1.6V at 5mA. That leaves (9V-1.6V) for the resistor. At 5mA the resistor value is R=(9V-1.6V)/5mA.
    Substutute your values as you like.

    Note that you should no draw more than 10mA from the 555 (datasheet). For your string of 1W LEDs you will need a driver circuit anyhow.
     
  7. BobK

    BobK

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    Jan 5, 2010
    Huh?

    From the datasheet:

    • Output Can Source or Sink 200 mA

    Bob
     
  8. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    Somewhat more than 10mA, but the latter part is correct.

    A useable LED driver circuit is in the LED Tutorial -- I only added it a few days ago.

    https://www.electronicspoint.com/got-question-driving-leds-t256849.html

    It would be simple yo make them flash alternately too :)

    Have a read of this and come back when you have read through to the end of section 3
     
  9. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    Yes, but that's for Vcc=15V and a considerable voltage drop across the internal output transistors. With ~10mA your'e on the safe side. As the OP doesn't seem to be too experienced, I thought I'd spare him some trouble chasing phantoms.

    It's amazing how many people seem to be reluctant to read a tutorial on the basics of LED control.
     
  10. davenn

    davenn Moderator

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    Sep 5, 2009
    there's a reluctance to read any of the tutorials ... period!! ;)


    Dave
     
  11. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    Reluctance? That adjective is too forgiving. I've begged some of our members and provided links to the pertinent sections. They would reply with total dismissal. As though I never mentioned it! I'd reply with asking if they did as I asked but their next reply would be another question and it wasn't about what they read in our tutorials.

    Chris
     
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