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press to see time wristwatch saves battery?

Discussion in 'Electronic Basics' started by Dan Jacobson, Dec 2, 2004.

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  1. Dan Jacobson

    Dan Jacobson Guest

    How much longer would the battery of a digital wristwatch last if one
    had to press a button to view the time? (Otherwise display is blank.)
     
  2. peterken

    peterken Guest

    lcd display, led display,.... ??

    for a led display things are fairly obvious

    for lcd display, much relies on the polarisation frequency of the display
    since it's the switching consuming the energy
    so for a definite answer on lcd..... sorry
     
  3. Ian Stirling

    Ian Stirling Guest

    LCD - bugger all.
    The battery if a backlight is not used, then you're looking at a battery
    life of 3 years or better for most watches.

    The backlight uses a LOT of power.
    A second of backlight may use as much as several hours of normal use.
     
  4. I just built a PIC circuit that turns off the LCD when it's not needed.
    With the LCD on, the current was 2mA. With it off, the current was 0.75mA.

    Now, invent a display that only turns on when you are looking at it. Or
    better yet, only turns on when you are paying attention to it.

    --
    Regards,
    Robert Monsen

    "Your Highness, I have no need of this hypothesis."
    - Pierre Laplace (1749-1827), to Napoleon,
    on why his works on celestial mechanics make no mention of God.
     
  5. Aplin17

    Aplin17 Guest

    Not much. Watches don't use much power.
     
  6. JM

    JM Guest

    [follow ups set to sci.chem.electrochem.battery,sci.electronics.basics]

    quoting:

    It would save just a miniscule amount of power, unless we're talking about a
    LED watch.
     
  7. A state-of-the-art watch circuit (oscillator and counters, without
    display) consumes around 80nA. To drive an LCD display you need
    microamps.
    Guess the battery's self-discharge is still dominant, so an always-on
    display does not shorten the battery lifetime.
     
  8. John Savage

    John Savage Guest

    Early digital watches (e.g., Clive Sinclair's "Black Watch" kit) used
    a red LED readout. LEDs were/are power hogs so the watch had a button
    to press for display. At uni I had an evening economics class where the
    lecturer wore such a watch. After pressing the button and glancing at
    his watch, there would be an arc of brilliant ruby red traced out amid
    the gloom of the dingy theatre as he swung his arm back to his side
    before the display timer shut itself down.

    Avoid using the backlighting and alarm if you wish to extend cell life.
     
  9. I think it is important to note that modern LED watches, use an LED
    backlight. YES, they make LED look-alike watches.
     
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