LED auto on/off

Discussion in 'The Projects Forum' started by keegan, Jan 15, 2015.

  1. keegan

    Thread Starter New Member

    Jan 15, 2015
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    I am trying to make a circuit that will turn on a string of LEDs for 4-6 hours off the day using a 555 timer.I could use some help designing the circuit. I have been searching the web but have not been able to find anything. Thanks for your help.
     
  2. #12

    Expert

    Nov 30, 2010
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    A 555 can't count that high. Look for a CD4060 or buy a 24 hour timer at a hardware store.
     
  3. WBahn

    Moderator

    Mar 31, 2012
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    More than a few minutes is asking a lot of a 555.

    What are your requirements?

    When you say 4-6 hours, are you implying that you want to be able to control it over a range of 4 to 6 hours, or are you just saying that if it's on for anything between 4 and 6 hours that that's good enough?

    How will it be turned on? Manually each time and then you just want it to go off somewhere between 4 and 6 hours later? Or do you want it to come on automatically at the same time each day? If so, how much drift can there be from when it comes on today versus when it comes on tomorrow?

    The approach taken to design the circuit depends one what is needed and what's important and what's not.
     
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  4. Dodgydave

    Distinguished Member

    Jun 22, 2012
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  5. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    What will be your power source ? AC to low V DC, solar & battery??
    On at sun down, off in 4--6 h.?
     
  6. keegan

    Thread Starter New Member

    Jan 15, 2015
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    First thank you all for your help. Sorry I was so vage with my expiation. I would like to to have it run for 4 to 6 hours then shut off. until the next day it will come back on at the same time of day and run for 4 to 6 hours again. As little drift as possible would be best. I would like to run it off of a lipo.
     
  7. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Using the suggested 4060 IC, AND 13 th & 14 th stages, output = 5.9 hours with clock set for 5.273 sec. Reset counter at lights out to sync. with day. May want to add more accurate time base later.
     
  8. WBahn

    Moderator

    Mar 31, 2012
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    Then you are going to need a pretty stable frequency reference. Probably the best one, if it is feasible, would be the mains frequency as this is extremely stable. If you use a something like a 555 circuit as your time base, then you will be lucky to get it to stay within a few percent. Let's say that you adjust it to be within 1% of what you need and then it stays exactly at that frequency with no drift, that means that your start time will move by nearly fifteen minutes a day. If you want it to drift no more than, say, one minute a week then your time base has to be accurate to better than 100ppm, which is a common spec for crystal oscillators. If you use a 32.768kHz watch crystal then, because they are specifically intended for watch and time-base applications, typically have tolerances in the 10ppm range. Plus, they are dirt cheap because they are manufactured is such huge volumes.

    Now, to get it to go on at the same time each day means that your clock divider has to map to a 24 hour period. That might be tricky with a 4060 as you don't have several of the lsb stages coming out and are also missing a middle stage. It's something that would be trivially easy to do with something like an 8-pin PIC microcontroller, but you need to have the software and programmer and know how to use it -- these aren't huge hurdles by any means. I don't know what the cost would be for a minimal set up (the software you need is free) and if you have any familiarity with programming at all you can probably be up and running in a day or so. Still, this may not be something that interests you.

    What are the voltage and current requirements for your string of LEDs?
     
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