Turn screen off without Android sleeping

Question

Is there any way to quickly toggle the screen off without making Android sleep?

For example, I sometimes like to use the Calm app when I sleep. But it keeps the screen on all the time. When I just use that app for 10 minutes, it's great that it keeps the screen on; but if I'm sleeping for hours, I would like the app to keep on running (playing sounds) and turn the screen off.

How can this be done?

Answer 1

Credit goes to Firelord for the basic method. Here is a time-delay shell script that turns off the backlight for my device, and apparently others' as well.

Create a file named "lcdoff" and copy the following into it:

#!/system/bin/sh
if [ -z "$1" ]; then
    echo "usage: `basename $0` delay"
    exit
fi
su -c 'echo getsu > /dev/null'
echo "Tap power button 2x quickly to restore"
sleep $1
su -c 'echo 0 > /sys/class/leds/lcd-backlight/brightness'

Make sure:

• The device is rooted.
• The script permissions are set to executable, e.g. by chmod 755 lcdoff.
• The script is located in /system/bin (scripts cannot be executed from /storage).

Then open a terminal app and enter lcdoff 10, to turn off the screen after a 10-second delay, lcdoff 30 for a 30-second delay, etc. To ensure that the processor stays on, simply enable the Android developer option "Stay Awake". Edit: Stay Awake only works while plugged into a power source -- see this answer for an alternative.

If you don't want to type the command in a terminal, you can launch the script as a custom action in:

• Total Commander
• Tasker
• Xposed Additions
• your app of choice

Answer 2

I had some trouble with the accepted answer as I'm not hugely familiar with shell scripting on Android/Unix/Linux so I thought I'd add my experience here for anyone in a similar boat.

To get this working with Tasker or similar the line you need is:

echo 0 > /sys/class/leds/lcd-backlight/brightness

For tasker put this in the 'command' field with 'Use Root' enabled, works like a charm. To disable simply switch the zero out for a 1, ergo:

echo 1 > /sys/class/leds/lcd-backlight/brightness

or lock and unlock the device.

So to answer your question about quickly toggling this behavior. Assign each of the above commands to a tasker task, then you can make use of the new long-press intercept in the latest tasker version to toggle the screen on and off without putting the device to sleep. Alternatively you can assign the command to a profile which triggers when your conditions are met.