This is a read-only archive of an earlier blog posting. Reasons for the
change are at http://blog.sensicomm.com.
The permanent version of this post - with comments (if any) - is at
http://sensicomm.blogspot.com/2015/10/pebble-watch-programming-to-extend.html
Pebble watch programming to extend battery
life.
These are my observations to date on
battery life with the Pebble classic watch. I figure the data will
be of interest to other watch face developers.
For my own Pebble watchface I wanted:
- Simple digital display with seconds
counter.
- Show current date.
- Large characters to be readable in poor light
conditions.
Once it was running, I wanted to
measure and optimize battery life. The watch reports battery state
in 10% increments, so I track the level changes as a function of
time.
Pebble has some hints online at developer.getpebble.com/guides/best-practices/battery-perform-guide/
. Basically, they say to do as little as possible when
servicing the timer ticks, and minimize the portion of the screen
that's updated.
The plot here was obtained with the
watchface shown in my previous post: blog.sensicomm.com/2015/09/pebble-watch-programming.html
. The green lines are the first version: I call the routines to
update everything on the screen every second. For the blue line, I
update the seconds display every second, but the rest of the
display only updates every minute. For the red line, I update the
seconds every second (obviously), the hour and minute update when
the minute changes, and the day updates every hour. The short
magenta line is like red, except I turn the backlight off (instead
of auto) and turn the watch off at night. Bluetooth was off in all
cases.
Observations:
- The
time from end-of-charging to 90% battery level varies widely, from
a few minutes to many hours. My guess is that the battery keeps
trickle charging even after the display shows charge is complete:
the shortest times to 90% were when I took the watch off charge
immediately, and the longest were when it was connected for an hour
or so after the indicated completion of
charge.
- That said,
minimizing unnecessary screen updates appears to make a significant
difference in power use: an additional day or so before the battery
drops to 40% remaining
power.
- I probably won't
bother keeping the backlight off or turning the watch off at night:
the savings don't seem that great and the inconvenience is
significant.
- The screen
backlight was in auto mode: it comes on for a few seconds when the
watch shakes. It did occasionally come on during all tests (except
magenta). No sure how much difference it made.
Again, this is for the Pebble Classic; no
idea how it works on other Pebbles.
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