# press to see time wristwatch saves battery?

D

#### Dan Jacobson

Jan 1, 1970
0
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.)

P

#### peterken

Jan 1, 1970
0
Dan Jacobson said:
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.)

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

I

#### Ian Stirling

Jan 1, 1970
0
In sci.electronics.basics Dan Jacobson said:
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.)

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.

R

#### Robert Monsen

Jan 1, 1970
0
peterken said:
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

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.

A

#### Aplin17

Jan 1, 1970
0
Not much. Watches don't use much power.

J

#### JM

Jan 1, 1970
0

quoting:
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.)

It would save just a miniscule amount of power, unless we're talking about a
LED watch.

M

#### Markus Lenggenhager

Jan 1, 1970
0

quoting:
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.)

It would save just a miniscule amount of power, unless we're talking about a
LED watch.

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.

J

#### John Savage

Jan 1, 1970
0
Dan Jacobson said:
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.)

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.

R

#### Robbie McFerren

Jan 1, 1970
0
I think it is important to note that modern LED watches, use an LED
backlight. YES, they make LED look-alike watches.
JM said:

quoting:
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.)

It would save just a miniscule amount of power, unless we're talking about a
LED watch.

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