In some cases saving as much power as possible is very attractive. Unfortunately I won’t have any real figures, but I have posted the links of others who have done the changes.
1. Run your Pi headless? Disable HDMI! This is reported to save about 20mA of power.
sudo /opt/vc/bin/tvservice -o
Note: Don’t forget you did this if you have to go troubleshooting with a monitor! Also, this doesn’t survive a reboot. I would recommend maybe adding the command to run once in your crontab a while after booting.
crontab -e @reboot at now +30 minutes -f /opt/vc/bin/tvservice -o
Note: Make sure the “at” command is installed, run “sudo apt-get install at” if not.
2. If you don’t need USB or the network adapter, you can disable both of those in one shot. This is reported to save a whopping 200mA of power.
echo 0x0 > /sys/devices/platform/bcm2708_usb/buspower
To re-enable the functionality:
echo 0x1 > /sys/devices/platform/bcm2708_usb/buspower
This might be very useful for projects that only need to “phone home” every so often so that battery power is conserved when it doesn’t need to talk to anything.
3. Down clock the CPU. No power figures are available yet, but being that the processor running slower will run cooler and use less power as usual, this will save at least some power and have the side effect of extending the life of the Pi. Edit /boot/config.txt and add the following lines anywhere (and make sure none of these are already defined):
force_turbo=0 arm_freq_min=250 core_freq_min=100 sdram_freq_min=150 over_voltage_min=0
Reboot to take effect. I did this myself, and here are the results:
Before reboot: pi@raspberrypi ~ $ sudo cat /sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_cur_freq 700000 After reboot: pi@raspberrypi ~ $ sudo cat /sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_cur_freq 250000
I noticed that the SSH session runs slightly slower, but running programs seem to still function ok. Your mileage may very, and the numbers can always be tweaked.