With PR 1.2 just around the corner, we will see a lot more apps take advantage of the new Qt 4.6 portrait mode features ( please do not take this to mean they will have them).

I wanted to remind everyone that enabling autorotation in any application including phone, and web browser will use more battery life, as your accelerometer will be switched on as a result.

accelerometer activation does not show up in CPU usage as it is low level hardware activity.

so Less Auto Rotation=More Battery Life.

Do you know how much? i think that the accelerometer isnt really heavy.

Dont have details, but will depend on the application, and what its doing with those accelerometer signals, so its not just a matter of the accelerometer usage.

It would be interesting to test the browser and phone with and without auto rotation, as I bet most people will have these running in the background.

hmmmmm
"a lot more" please be specific. this is rather vague and sounds that you are just scaring us

The current browser has the accelerometer/portrait mode disabled by default. However, most people have enabled it by pressing ctrl-shift-o. I have yet to see anyone report additional power usage based on having it enabled (assuming ctrl-shift-o actually does turn on the accelerometer and it is off by default).

An easy way to test power consumption will be to turn on the setting where the phone app opens when rotated.

I don't think it would be that great of a power drain. I would much prefer to have auto rotation in most apps.

@slender , apologies if this comes across as alarmist. not meant to be. just a reminder.
as a developer who is about to add potrait support to my apps I thought it might be useful to remind people that there is an impact. as usual when it comes to battery YMMV.

Heres the warning from the dev Qt4.6 dev guide.

The ST-made accelerometer itself most likely draws the 400 µA as specified in the datasheet from its 2,5-3,3 V supply as it's most likely set to the lowest refresh rate of 100 Hz, so the sensor draw is certainly not "a lot more". Not sure how the drivers handle it, but reading three 8-bit values over I2C, possibly comparing them to a few previous readings and then placing them to the specified location should not be "a lot more" power consumption either, even when done at 400 Hz (the maximum for this model). The accelerometer even allows setting limits within the control registers and just sitting idly while the accelerometer does all the job and generates an interrupt when the limits are exceeded (e.g. close enough to ±1 g to tell if the device has been turned). Plus it's most likely turned off like the ambient light sensor is when the screen is locked and the device in general goes to powersave mode...

The increased battery draw is more likely connected to the animation requirements for orientation-aware software; it's one more (and possibly frequently-used) animation to push through the GPU and possibly even doing some CPU work to rearrange and format the items being viewed and remapping the coordinates. Just flipping the view without any animations is painfully slow even on desktop systems (anyone who has tried to use the pivot capabilities of most flat panels computer displays are most likely familiar with the flickering and messed up desktop elements during the surprisingly long time it takes for the system to realise that everything is standing on its side now), so its drawing "a lot more" power even in systems that are designed to be orientation-sensitive is hardly a surprise. The effect can be cool, yes, but it does use some power - there's no such thing as a free lunch. I have currently all turning interactions on as I will charge the device every night anyway - the automatic rotation must be done really badly in the new Qt for it to actually reduce battery life by a non-insignificant amount. I wouldn't worry too much.

Turn off auto-rotation. Reduce screen brightness. Turn off all eye-candy. Disable GUI. Turn the device into one big console. Avoid using the phone app.

I'm sure the battery will last longer.

Come on people - even if autorotation *does* use more battery, I'm still gonna use it because it's cool and practical. All other touchscreen devices have it and use it. Are some of you guys willing to give up everything but the terminal?

Other platforms have live desktops, multiple social networking widgets, animated eye-candy - but for some of the Maemo crowd, even autorotation is too much. I just don't get it.

I think the accellerometer is always turned on, since we can use it to snooze the alarm, isn't it? or the CPU will only enable power to acc chip once the alarm triggered?

Brilliant mention of this as a reminder,
turning off this feature may get interesting where it is used in other apps.

Perhaps we could make a script to lock this down
and only enable it for specific applications/usages
on an as-needed basis.

To be sure it is not a large amount of energy but it adds up over the day.