Lean Computing: Lowering power consumption without sacrificing utility

[2twisty]

I'm starting this thread here since I think that many Pi users will be of similar mind, and many of us use XBIAN for a media center.

I'm starting this as a place to report things that I do/explore as I try to make my media center functional but use as little power as possible.

Some background:

My wife and I plan to go off-grid within the next 5 years. We want to preserve as much ouf our technological lifestyle as possible. One place that we will have to make major changes is in power use. The Pi is one step toward that.

I've run (and still have) some very serious hardware at my disposal. I have an Asus KGPE-D16 Dual Opteron board with 2 Opteron 6128 8-core CPUs (2GHz) and 24GB of RAM and a RAID5 array. At one time, I had my array up to 20TB.

I had a separate 6-core AMD that ran my Windows Media Center.

Then, my priorities changed. Then I got the Pi. I replaced my 46" TV that pulled 340W with a 39" that pulls 130W. That's still a lot of power when you're talking about an off-grid situation.

I've been fighting with my TV to find a way to make it go into standby using CEC codes, but apparently the HDMI Spec (My TV is 1.4) doesn't yet REQUIRE support for the standby command, and the manufacturer (Insignia, house brand of Best Buy stores) flatly REFUSED to give me any info about the vendor-specific codes that can be used to control the set. They claim it's "proprietary."

Asshats.

Anyway, I've got a better idea anyway: I'm going to create (or buy, haven't decided yet) a relay board controlled by GPIO to cut the power to the TV. This will use even LESS power than running on Standby. My initial testing (by unplugging the TV while the Pi is running) has been encouraging.

If there is a video playing I get an "unsupported mode" error. However, if it's just sitting there at the menu, it seems to come back ok. So, in a "screen saver" situation, it likely would work out.

I will keep this thread updated with the results of any testing and modifications. I'll have to write a special screen saver add-in for XBMC for the Pi to control the GPIO port, but I'm hoping that won't be too difficult.

If you guys are doing anything special to reduce power consumption, please add it to this thread. If any of you are already using a relay board to switch 110V AC, please provide links to purchase or designs. No need to reinvent the wheel.

[rikardo1979]

my 5c to this, i think that cutting off power to any device in chain connection without proper shutdown/switching off is a bad idea

[CurlyMo]

I use remote controllable switches from brands such as http://www.coco-technology.com/en/home/ to pull the power from my whole TV stack. I control these things from my RPi with my own code: https://github.com/CurlyMoo/433.92-Raspberry-Pi/. Never ran in any trouble. However, relays would be fine as well because these CoCo devices essentially work the same.

[2twisty]

@rikardo1979,

If it's a device that has open files, then yes, I agree with you. However, a TV at most has some flash memory that remembers things like your channel scan, current volume level, etc. I would be very very surprised if those preferences were contained in an active (and therefore corruptable) file. Over the years, I've unplugged items like TVs and Tunner/Receiver/Amplifiers with no ill effects.

I do plan to also put my external USB drives on a relay switch, as well. However, as part of the "sleep" procedure, I'll issue the needed commands for "safely remove." I'll probably just use a script to unmount the filesystems, since that will sync any data, then issue the power-down command.

Do any of you have experience with items like the CoCo products that CurlyMo mentions, but are deesigned for use in the US and switch 110V? I'm also not looking for something very complex -- something with a couple screw terminals for the relay trigger and a switched 110V outlet is good enough for me.

However, I can't decide if I want to have the TV on a NO relay or a NC relay. I think I'm going to go for NO, so that if the Pi powers off, so does the TV. I don't see that have any ill effects since I won't be using the TV for anything other than a display for the Pi.

The external USBs, however, are another story. I can't really decide, but I am also leaning toward NO. In the rare case that the Pi is not shut down properly (and therefore safely unmounting the USB devices), it won't be any different than when you have a power outage. Also, since the data on these drives is mostly only being read, powering them down suddenly isn't as catastrophic, since its unlikely that there will be any open files. I'm still debating that one...

What are your thoughts?

I'm also thinking of cramming all this stuff into a box. Right now, with all the USB hardware and power cables, the area under my TV is an absolute rats nest! What do you guys do to control the wires?

[BartOtten]

(7th Mar, 2013 11:47 PM)2twisty Wrote:  What do you guys do to control the wires?

I play a flute and once they are up I spray them with hairspray for a few hours. Once done they stand nicely. Make sure to vent the room for a while as all the gasses can make you sick.

[mk01]

is anybody really turning PI off ? the 'concept' issue for me is no convenient way to turn it again on.

HDMI CEC is working nice with the other devices I have, TV, AV receiver, blue ray, separate Amplifier, even is possible to setup what should be on and what off in relation to specific HDMI input port chosen on the AVreceiver, or even Samsuing TV can control (turn on / off) all the devices in groups. PI can send CEC signal, or receive such, but there is no kernel with huber / suspend support, so only way is go to power off.

and only known solution for me to turn again on is replug power.

so currently PI is running all the time, but instead of powering off, screensaver acts as CEC control. When started, all devices are going to suspend / off.

And all possible cabling simplified byt buying AVreceiver now having power cord and and hdmi. still two more than wanted, but ...

[CurlyMo]

If i turn off my RPi i can't control some of my light in the house, so that's not an option

[mk01]

don;t be silly

http://www.youtube.com/watch?v=bI1tSBN6r4s

[CurlyMo]

Precisely