Fix for a longstanding Raspberry Pi annoyance: Getting the monitor into powersave mode after a period of idle time - turning off the backlight.
Here's a quick tweak that seems to work fine on native HDMI and VGA (via adapter*) monitors. Hopefully helpful to others.
Background: I've played with Linux Power Management commands, utilities, screen savers and such in attempts to get Pi's to turn off (standby) monitors when idle. I recently hit upon a couple of Raspberry Pi config option that seems to do the trick - not really sure when/where it appeared, but it does switch off the HDMI when Display Power Management (DPMS) is triggered, as opposed to simply blanking the screen. Works on Raspbian Stretch & Buster and recently on RaspOS
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April 2024 Update: I STILL had to fiddle around to get my RPI5 to turn off the display!
Wayland appears to be the default display manager under RaspOS Bookworm with no screensaver (that I could find). I fell back to X11 (for other reasons too) but STILL had to install xscreensaver and Power Manager for GUI and add consoleblank to cmdline.txt (now in /boot/firmware) as outlined in original 2018 Step-by-Step below.
Jan 2022 Update: It looks like this is finally fixed/documented on Bullseye - that is, hdmi_blanking seems to be set by default and adjustable via raspi-config (Display->Screen Blanking) . RPi step by step is HERE. In a nutshell: Screensaver or Power Manger are still required to set monitor DPMS sleep/off/standby for Pi's that boot into GUI. Adding "consoleblank=<time>" to /boot/cmdline.txt will take care of blanking in console mode. Tested on RPi 3B+ and RPi4. There may still be some work to do according to https://github.com/RPi-Distro/repo/issues/283, but it seems to work fine for me (famous techie line!)
Fall 2021 Update: Rescued from http://ventures.tpedersen.net/projects/puttingraspberrypimonitortosleepdpms.
In spite of a recent Buster Update ... I STILL manually adjust /boot/config.txt & /boot/cmdline.txt to get HDMI into standby mode. Works on RPI 4 too!
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The fix involves editing a couple of key configuration files - as always remember to make a backup copies before type-o'ing in these files! Use sudo to edit files in boot partition *and* be careful!
Edit /boot/config.txt (RPi's main System Config File).
// Note: raspi-config includes this option on bullseye and > //
Add the following line to force HDMI output to switched off when DPMS is triggered. This config option was not explicitly defined in my Raspbian (Stretch) config.txt - apparently defaults to 0/off.
hdmi_blanking=1
I added this line below hdmi_mode in config.txt, but it probably doesn't matter. See complete details in https://www.raspberrypi.org/documentation/configuration/config-txt/video.md. There are notes/considerations.
Make sure Screen Savers are installed/configured to take advantage of hdmi_blanking.
For Console Mode (no Desktop UI) set console blanking ...
Check current setting of consoleblank kernel parameter, it sets the inactivity time. It defaults to zero (returns 0)
$ cat /sys/module/kernel/parameters/consoleblank
0
Edit (sudo) /boot/cmdline.txt to set time in seconds to turn off monitor when Pi is in console mode.
Carefully add the string "consoleblank=<numsec>" to /boot/cmdline.txt - MUST be a single line text file like this:
// Note: Bookworm release moved cmdline.txt to /boot/firmware directory //
$ cat /boot/cmdline.txt
dwc_otg.lpm_enable=0 console=serial0,115200 console=tty1 consoleblank=300 root=/dev/mmcblk0p7 rootfstype=ext4 elevator=deadline fsck.repair=yes rootwait
For Desktop GUI set Display Power Management (DPMS) via screensaver or power manager applications - you may need to install these.
Screensaver:
sudo apt-get install xscreensaver
sudo apt-get install xfce4-power-manager
See RPI Screensaver doc @ https://www.raspberrypi.org/documentation/configuration/screensaver.md for complete details.
Reboot and check your work!
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As they say in IT - Works for me! Hope it works for others too.
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Couple of random notes:
There are some very interesting BIOS-like options in RPi config.txt file. Also a nice write-up @ https://www.raspberrypi.org/documentation/configuration/config-txt/
An FYI from http://saf.bio.caltech.edu/saving_power.html: "...for an LCD display there is often no difference between standby, suspend, and off"