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Discussion in 'The Projects Forum' started by yabasoya, Oct 8, 2009.

  1. yabasoya

    Thread Starter New Member

    Oct 8, 2009
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    Hello everyone.. Im looking to build a very simple circuit. Basically what I need to do is build a timer circuit that creates a short(or trigger a relay) every 30 - 90 seconds. The operating voltage will be about 4.5 vdc.

    I have a camera flash that goes to sleep after 90 seconds of inactivity and I need to short 2 pins every 30 - 90 secs. to keep it alive even if just for a millisecond. Any tips or suggestions appreciated. Thanks.
     
    Last edited: Oct 9, 2009
  2. hgmjr

    Moderator

    Jan 28, 2005
    9,030
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    Take a look at the material in Bill Marsden's blog on this website. His presentation on the 555 timer contain some clever circuits that could serve as the basis of such a delay timer.

    hgmjr
     
  3. yabasoya

    Thread Starter New Member

    Oct 8, 2009
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    It's too bad that every image is unavaiable ans shows a red X
     
  4. Wendy

    Moderator

    Mar 24, 2008
    20,765
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    Where is that? I'm aware of no broken links.
     
  5. yabasoya

    Thread Starter New Member

    Oct 8, 2009
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    Funny.. I just checked and they're all there. I swear that last night and this morning there were red X's all over the place.
     
  6. yabasoya

    Thread Starter New Member

    Oct 8, 2009
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    Am I correct in saying that I need a high output of .5 seconds and a low output of 59.5 seconds? Im messing with some 555 calculators.
     
  7. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    It depends.

    You might consider using a 4N25 optoisolator with the 555 timer driving the LED side, and have the optocoupler output short the two pins.

    You could have the timer stay high for 60 seconds and go low for a brief period, or have it stay low for 60 seconds and high for a brief period; whichever is easiest.
     
  8. Wendy

    Moderator

    Mar 24, 2008
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    You can set it for whatever, a simple transistor can act as a reasonable switch, driven by a 555. If you use a CMOS timer you can get the power requirements way down there.

    When you refer to a short I'm assuming a switch, and not shorting the power supply. You can short a power supply if the batteries don't have much juice, and use large capacitors to keep the timer in power.
     
  9. yabasoya

    Thread Starter New Member

    Oct 8, 2009
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    After a little research, it appears that I a can go the 2 transistor flashing LED route and instead of the LED, I can use a relay to close my connection that I need. This will allow me to use the 4.5 volts that I can get off of the flash.
    I am having a little trouble with these calculators and the times on/off. All of them require me to input the R1, R2, and C1 values and then it will tell me the times on/off that they make together. What I need is something that I can input the times on/off and it will give me the values for R1, R2, and C1. Anything like that exist?
     
  10. Wendy

    Moderator

    Mar 24, 2008
    20,765
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    Probably not what you're looking for, but...

    [​IMG]
     
  11. yabasoya

    Thread Starter New Member

    Oct 8, 2009
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    So I ran across this schematic. I am going to substitute a relay for the LED. How do I figure out what values I need for the resistor and the capacitor? Basically I need it to "flash" once every 30 to 90 seconds. I dont care what that number is.
    [​IMG]
     
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