countdown timer w led

Discussion in 'The Projects Forum' started by stillafloat, Apr 16, 2013.

  1. stillafloat

    Thread Starter Member

    Apr 16, 2013
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    i am looking to do the following with my breadboard...

    1. have a count down timer that can be reset via a rocker switch
    2. count down time presets (can select 24hr, 12hr, 8hr, 6hr, or 4hr)
    3. after a preset time it achieved an LED will flash for 5 mins on and 5 mins off until switch is pushed t reset time again.
    4. be battery powered via 3.6v button battery

    i am really new to circuitry so go easy on me :D ive read about the 555 and 4017 ic's. am i headed in the right direction?

    again any help would be amazing..
     
  2. MrChips

    Moderator

    Oct 2, 2009
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    How accurate do you wish your times?

    For example:

    24hr +/- 15min

    4hr +/- 2min
     
    stillafloat likes this.
  3. stillafloat

    Thread Starter Member

    Apr 16, 2013
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    as accurate as possible but keeping battery usage to a minimum.. +- 15 min on 24hr time is fine is thats the best we can do
     
  4. MrChips

    Moderator

    Oct 2, 2009
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    Don't you just love it when people request:

    as ____ as possible

    fill in the blank with

    accurate
    stable
    low cost
    large
    small
    high
    low


    Give us some numbers.

    You can have +/- 1 second if you ask for it.
     
    absf likes this.
  5. stillafloat

    Thread Starter Member

    Apr 16, 2013
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    lets get it within +- 3mins on 24hr

    i know when my wife asks for $20 i dont have an option for $19 or $18 its $20 so i just assumed the rest of the world worked like this ;)
     
  6. #12

    Expert

    Nov 30, 2010
    16,321
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    $20 is always $20.0000000
    The problem is, it's hard to do 24.0000000000000000 hours.
    It is always impossible to be perfect so we need to know how much less than perfect can you work with.
     
  7. MrChips

    Moderator

    Oct 2, 2009
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    But when she puts $20 worth of gas into the tank, how much actual gas did she put into the tank?
    That's how the rest of the world works.
     
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  8. stillafloat

    Thread Starter Member

    Apr 16, 2013
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    if we can stay within 0.25-0.5% on either side would be preferred..

    and if i sound like i still have training wheels on its cause i do, still leaning, but learn a heck of a lot better by doing.. i never was a good book learner
     
  9. stillafloat

    Thread Starter Member

    Apr 16, 2013
    41
    0
    so the n555 is pretty inexpensive an only 8 pin so maybe this is the rout I need to go? I read that it has an accuracy of 1% give or take. is this correct?
     
  10. gerty

    AAC Fanatic!

    Aug 30, 2007
    1,153
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    The timer may have that accuracy, but the associated capacitors will have change over time, and your timing will drift.
     
  11. stillafloat

    Thread Starter Member

    Apr 16, 2013
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    i am looking for the timing to hold fairly steady for 3 months. should i be looking at a different timer?
     
  12. gerty

    AAC Fanatic!

    Aug 30, 2007
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    In post #1 you state you want to power it from a 3.6 v battery. A 3.6 v battery won't last for 3 months. A 4017 needs a minimum of 3v to run and a 555 not much different. I would use a different power source. Do you need repeatability over 3 months, or do you want continous timing over 3 months
     
  13. stillafloat

    Thread Starter Member

    Apr 16, 2013
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    The battery i can def change, i wanted to use button batteries for their low profile but i see how it would drain fairly quickly.

    I need the timer to run 24hrs for 3months. power wise i can run off a different power source to achieve that part of it. The timer runs down from 24hours to 00:00 and then activated a single LED to flash 5mins on and 5mins off until a reset button is pushed. Once the reset button is pushed the sequence starts all over.

    Sorry for my lack of terminology im still learning :) and thank you for taking to time to help.
     
  14. joeyd999

    AAC Fanatic!

    Jun 6, 2011
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    These two requirements are pretty much mutually exclusive (in the context of your request).
     
  15. MrChips

    Moderator

    Oct 2, 2009
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    I am not sure what you mean by flash 5 mins on and 5 mins off.
    Flash at what frequency, about two times a second?

    What purpose does it serve for the LED to be off for 5 mins?
     
  16. stillafloat

    Thread Starter Member

    Apr 16, 2013
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    0
    Timer counts down to 00:00 and activates LED to flash for a 5 min period and then stops flashing for 5mins and then start flashing again for 5mins, etc. So in a 10min span the first 5 mins the LED will be active and the second 5mins it will be out. untill a reset button is pressed to cycle all over again starting at 24:00 and counting down.

    Flash rate of once a second.

    Turning the LED off for a 5min period i figured would help conserve battery. But you could argue that if i increased the flash frequency from once a second to onces every 2 seconds we can just have the LED continually blink without the 5min off cycle.

    somehow in my mind it makes sense. But not 100% sure.
     
  17. MrChips

    Moderator

    Oct 2, 2009
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    That's what I suspected you were attempting to do.

    If your objective is to conserve energy I would do the following:

    1) choose a high efficiency LED
    2) lower the current to the LED
    3) reduce pulse-width to the LED
    3) reduce the frequency, i.e. increase the time interval between flashes, e.g. 2 seconds
     
  18. stillafloat

    Thread Starter Member

    Apr 16, 2013
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    I will def use your recommendations in the build. thank you. Now i just need to determine the best IC to use can you help me along with this? Would love to get the pieces needed to test.
     
  19. MrChips

    Moderator

    Oct 2, 2009
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    Now that we have eliminated the 5-min off cycle that simplifies things a bit.

    First solution:
    Use a microcontroller. This will give you the lowest cost, lowest part count, lowest drift, lowest footprint, lowest operating voltage, lowest current drain.

    Second solution:
    Use CMOS components, for example, a CMOS LMC555.

    When I find the time I will put together a design for you.
     
  20. MrChips

    Moderator

    Oct 2, 2009
    12,449
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    Here is a possible design using standard CMOS circuits:

    [​IMG]

    This takes six ICs.

    Still a lot easier to do with one IC.
     
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