is there a way of delaying an led without using a 555 timer

Discussion in 'The Projects Forum' started by james555, Dec 20, 2014.

  1. james555

    Thread Starter New Member

    Dec 20, 2014
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    perhaps a transistor and capacitor combo.. it does not have to be precis just a second or two would do
     
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    What LED current?
    What LED Vf?
    What supply voltage?
    How long an interruption of input power before the next timing cycle?
    Can we use R,C, transistor and diode?
     
  3. wmodavis

    Well-Known Member

    Oct 23, 2010
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    Arduino?
     
  4. james555

    Thread Starter New Member

    Dec 20, 2014
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    3v (2AA)

    yeah i was thinking a resistor/ cap combo would do

    using a arduino in this basic application would be like using a shot gun to kill a fly.. it would work but im looking for basic.. as basic as can be
     
  5. wayneh

    Expert

    Sep 9, 2010
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    It will - just experiment. You'll need a relatively large capacitor. If you don't like the behavior you get, you'll have to use something more elaborate.
     
  6. wmodavis

    Well-Known Member

    Oct 23, 2010
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    Didn't see in your OP anything about looking for 'basic as can be'. Just responded to what you said with a possibility you could consider based on your stated criterion.
     
  7. #12

    Expert

    Nov 30, 2010
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    Did your last job involve designing modern cars? :rolleyes:
     
  8. wmodavis

    Well-Known Member

    Oct 23, 2010
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    Nope. Not into plumbing.
     
  9. #12

    Expert

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    Good. I wouldn't want the water in my tail lights to be regulated by a microprocessor.
     
  10. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    Overkill. A PICAXE would do. 28-pin, of course.
     
    Last edited: Dec 20, 2014
    #12 likes this.
  11. donpetru

    Active Member

    Nov 14, 2008
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    Modify the following circuit (you have to adapt it to operate at 3V):
     
  12. takao21203

    Distinguished Member

    Apr 28, 2012
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    use a 2n7002, with a 4.7 M Ohm resistor, a small capacitor will do.

    Higher value resistors are difficult to get even though, they exist.
     
  13. james555

    Thread Starter New Member

    Dec 20, 2014
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    hay man it ok.. i should have specified

    in fact i'll be using a mp board later in my project
     
  14. LDC3

    Active Member

    Apr 27, 2013
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    With only 3V, the BJT would probably work well, but at higher voltages I would think a MOSFET would be better.
     
  15. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    Here is the brute force way, but it has several problems, the least of which is the huge capacitor required. It also has a "recycle" problem, in that it takes a relatively long time for the timing capacitor to discharge to get ready for a new delay cycle after the switch is opened. Note that this is about the best that can be done with this circuit. If you make R2 smaller to discharge the capacitor faster, then it wastes a lot of power while the switch is closed.

    251.gif

    Here is a better way. This reduces the capacitor size and improves the recycle time

    251a.gif
     
    Last edited: Dec 20, 2014
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