Choices for 7-segment LED clock for long battery life

Discussion in 'The Projects Forum' started by zcream, Jan 11, 2012.

  1. zcream

    Thread Starter Member

    Feb 21, 2009
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    Hi! I wanted to design a sunlight readable clock with a long battery life. And hopefully a choice of easily replaceable AA batteries.

    I guess the top choice would be a 7-segment led display for brightness and a PIC of some sort.

    I would need a switch to turn it off and on.

    What other choices should I make to make sure it runs off a AA battery and that its sunlight readable and has a battery life as long as possible ?
     
  2. joeyd999

    AAC Fanatic!

    Jun 6, 2011
    2,675
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    Sunlight readable LED != long battery life.

    Perhaps you should consider LCD?
     
  3. wmodavis

    Well-Known Member

    Oct 23, 2010
    737
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    LEDs, as joeyd said, may not be your best choice because they really are tough to read in sunlight somewhat variable depending on color but IMO do not meet that criterion. Take a working one out into the sunlight and see for yourself. You probably do not remember LED wrist watches. I only could tell time in the dark.

    And they are really current hogs compared to LCD. And LCDs are definitely preferred in sunlight. Those LED watches needed battery replacement way too often.

    LEDs do have the advantage of being a simpler to design.
     
  4. bwack

    Active Member

    Nov 15, 2011
    107
    10
    Since you are looking at using a pic, have a read through the "Low-Power Design Guide" from Microchip.

    http://ww1.microchip.com/downloads/en/AppNotes/01416a.pdf

    i found it under here:
    http://www.microchip.com/en_us/technology/xlp/products.html

    btw: James Bond had a similar watch as you describe, On his WRIST :D
    edit: the link with some pics of it: http://forums.watchuseek.com/f2/your-favourite-vintage-digital-watch-560215.html
    I'm wondering if a contrast-sheet would help like they have used on these clocks ? (sooted plastic covering the 7segments)
     
    Last edited: Jan 11, 2012
  5. wmodavis

    Well-Known Member

    Oct 23, 2010
    737
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    "I'm wondering if a contrast-sheet would help like they have used on these clocks ? (sooted plastic covering the 7segments)"

    In designs I was involved in back in the late 60s we covered the LED displays with a monochromatic plastic filter lense to help minimise washout from ambient light. The surface was matte to also minimize reflection.
     
  6. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    6,357
    718
    If you made the display button light up the LEDs for only as long as you held down a momentary switch, say 2 seconds, it could last quite a while.

    I had a watch like that in 5th grade, I was the coolest kid in school, pushing the side of the watch, and you could see 1/4" tall LEDs showing the time. Check it too often, and you needed a new battery every week.

    For yours, it'd be about the same, but say, a month lifetime using AA batteries.
     
  7. zcream

    Thread Starter Member

    Feb 21, 2009
    20
    0
    How about a sunlight readable led with a momentary switch ?
    So the time is only seen when you press the button, as stated above..

    At this time, I dont think I have the expertise to design for a lcd.

    I am just reading the low power document listed above
     
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