Small & Flexible: Back-of-LCD variable power consumption

Linus · Post by **Linus** » Tue Mar 08, 2005 11:06 am

This is my new PC:

Origins:

My last PC had a Celeron 566A permanently overclocked (through a broken pin) to 850 MHz and stuffed into a tiny flexATX case. It was a good little box, reasonably quiet and powerful enough for most things I used it for (playing music & movies, mostly). But it took 12 hours to encode DivX movies, which I found myself doing a lot. I dreamt of a new, faster PC, but didn't want it to use any more power while doing easy things like encoding mp3s. The Pentium-M sounded wonderful, but was too far off in terms of price and desktop availability.

Then I read Deep UnderVolt/Clock: 4.7W CPU PC, and realized that dynamic over/under-clocking was indeed possible without Cool-N'-Quiet or Speedstep. By adjusting the CPU speed (from windows!), I could maximize power efficiency for each task, running very slowly for playing mp3s and ramping up for more demanding tasks like video encoding. I decided to build a new PC with the following priorities, from most to least important: high power efficiency, small size, quiet operation, simple styling, and gaming prowess (more detail in my investigation thread, Back-of-LCD variable power consumption PC).

Components:

Case: Silverstone Lascala SST-LC02 - Chosen for its small size (especially height) and relative lack of sacrifices in expansion and cooling. I was worried about the power supply, but it actually seems to be quite good - it was pretty quiet stock with a single slow 60mm fan, but I've removed its cover (along with the fan) and it runs well enough with airflow from the other two fans.

Motherboard: Biostar M7NCG 400 - Chosen for its microATX form factor (leaving a little room for 2.5" HDD and firewire bridge) and compatibility with 8rdavcore.

Processor: AMD Athlon XP 2200+ 1.35v Barton - Originally tried a Thoroughbred 1700+, but I managed to fry it while the cover was off the PSU. Oops...time to upgrade to a Barton. I've been able to run this one anywhere from 285 to 2220 MHz - not a bad range.

Heatsink: Thermalright SLK-900A - Mostly bought because it was cheap and on the recommended list, it's worked out well. Can't hurt that the fins are oriented vertically when mounted on my motherboard, giving a little convection "assist".

Memory: 2x Kingston 256MB DDR PC3200 CAS3 - Cheap, and happy enough running at 193 MHz at CAS2

System HDD: Fujitsu MHT2060AH 2.5" 60GB - Probably not as quiet as the 4200-rpm -AT series, but extremely quiet to my ears. I've mounted it on some mousepad wrist-rest material to prevent transmission of vibrations to the case, and it stays cool with the nearby PCI-slot air intake.

Data HDD: Maxtor DiamondMax 9 3.5" 160GB- Certainly not quiet, but it's rarely on for any length of time.

Optical Drive: Panasonic CW-8123-B laptop CD-R/RW/DVD-ROM - A laptop drive is required for this slim case, and this one was the cheapest slot-loading laptop drive out there. It's worked well so far.

Firewire Bridge: Two-device Firewire 400 (1394a) - Based on the Oxford 911 chipset, which is supposed to be one of the fastest. I wired up the data HDD and the optical drive to a switch so they can be turned on and off without rebooting.

Fans: 1x Chinaflo 92mm on the CPU, 1x Japanaflo 80mm above the PSU, both directed out of the case and controlled by Zalman Fanmate 2's. Extremely quiet if not inaudible at 5v. The 92mm makes a fair amount of noise at 11v, but it also pushes a lot of air for those times that noise isn't a concern.

Cable-Management Box: Homebrew design using 0.5" plywood painted black. I needed a slightly higher LCD mount to give room for the video cable under the case, and decided to build this thing to hide some cables while I was at it.

Temps:

A graph is worth a thousand words...

The system HDD temp varies from 28-35 degrees Celsius depending on the fan setting and activity level...well within the limits of the laptop drive.

Power Consumption:

Varies from 37W at minimum speed with firewire drives off to 170+W running Prime95 at maximum speed with the data HDD on.

I developed a simple benchmark for encoding efficiency in Lowest Power Consumption for DivX Encoding - basically using the SiSoft Sandra Multi-Media Integer score (supposedly indicative of encoding speed) and dividing it by the total system power consumption. My old Celeron scored 85.6 ints/watt, and the new one hits 220 ints/watt. Two-and-a-half-fold increases in encoding efficiency make me happy.

Also note that the highest efficiency is extremely close to the stock speed of this processor - interesting.

More Pictures:

Cable box in the painting stage

Closeup of the LCD mount - it's pretty solid.

Back view of the mounted LCD and closeup of the data HDD/optical drive switch.

The mounted motherboard, with cables routed behind.

Everything in except the tray for the data HDD and optical drive.

Questions and comments welcome!

Tibors · Post by **Tibors** » Wed Mar 09, 2005 6:13 am

Awesome project. This is really hiding the PC and keeping the multimedia. But do you have to put it on the edge of that rickety table. I can see it falling

What were the ambient temps when you measured your case and CPU temps?

Post by **Ralf Hutter** » Wed Mar 09, 2005 6:26 am

Completely OT, but is that a real log cabin you're living in?

Linus · Post by **Linus** » Wed Mar 09, 2005 6:59 am

Tibors - Actually, an additional benefit of the cable management box is that it adds ballast and helps balance the whole system by adding weight in the front & bottom to counteract the case mounted on the top & back. It's actually stable enough to right itself from about 30 degrees forward or backward. I'm guessing the whole contraption weighs at least 25 pounds, so I'd have to hit it pretty darn hard for it to fall over.

Ambient temperatures were within a degree or two of 64F (~18C).

Ralf - Yep, it's actually a log cabin. Ironically, though, now that I've got a very small-footprint PC, we've moved from our little ~380 sq. ft. cabin to a ~1100 sq. ft. duplex. So I've got plenty of space for a more normal system that could be more powerful and quieter, but less stylish (in my opinion).

The system is now on the top shelf of a short bookcase (ahh, the joys of a slim system!) until I get or make a better end table/computer desk thing.

SometimesWarrior · Post by **SometimesWarrior** » Wed Mar 09, 2005 11:33 pm

Cool setup! I like your temperature graph as well--it's a very good way to explain what's happening. It makes me wish SPCR used similar plots in their reviews.

Linus · Post by **Linus** » Wed Dec 07, 2005 10:22 am

Now that I've run this system for the the better part of a year, I thought I'd write an update.

Over- and under-clockability with 8rdavcore hasn't changed significantly since the graphs above. At first, the computer would only run at 1.25v (@ < 1.5GHz) after it had warmed up and even then would often crash after playing mp3s for a while and cooling itself off again. Now that the everything is fully "burned in", though, if it can get itself running at 1.25v (still won't do it cold), it's perfectly stable. Power consumption seems to have gone up a watt or two from my original numbers, but I've brought it back down through lowering the voltage and running st2ctl for halting the processor.

The switched firewire system works, but I've had issues with transfer speeds. I can move a ~700MB file to the 3.5" Maxtor in 10-20 seconds, but moving or copying the same file FROM that drive takes 10+ minutes. I've tried replacing my 1394 cable with no change in performance. Any ideas as to what might cause this? I thought the Oxford 911 chipset would prevent this kind of issue, but in retrospect it may have been better to go with plain old USB 2.0.

The only other issue I have with the system is that the motherboard's on-board sound is a bit worse on signal-to-noise than I'd like. I can hear quite a bit of hiss during quiet moments on DVDs. I may try an M-Audio Transit to fix this.

Other possible improvements:

Attempting to run the LCD off the 12V rail on the PSU. The brick power supply for the LCD is probably not all that efficient and I should be able to lower total power consumption by running it off the computer's PSU. The increased load may bump it up to a higher point on its efficiency curve too.

Changing out speakers (currently Klipsch ProMedia 2.1's that draw 20W all the time) for a Sonic Impact T-Amp and more sensitive speakers. The T-Amp uses a modified Class D design, which being switched is ~90% efficient rather than ~50-60% for the Class A/B amp in the Klipsch subwoofer. This should cut my audio system power draw to 10W or less.

With these changes, I'm hoping to bring minimum overall consumption (computer, LCD, & speakers) below 75W - not bad for a machine that can ramp up to 2.2 GHz for serious processing tasks.

If anyone has any questions or comments, let me know!

Fat_bloater_dave · Post by **Fat_bloater_dave** » Wed Dec 07, 2005 11:45 am

Mmmm, this is such a cool idea. and you have done it so well. Good work.

Dragon Puppy · Post by **Dragon Puppy** » Fri Jan 13, 2006 10:20 am

I've too thought about hiding the pc behind the monitor , but my plan would use those bendable VESA extension arms for lcds and sandwich the computer in betwean them and you get an uncluthered(sp?) worktable when comp "hangs" in the air. One problem would be the HDD if you moved it when powered , puff goes the HDD.

djnotepad · Post by **djnotepad** » Fri Jan 13, 2006 1:41 pm

really awesome project with really awesome pictures and explanations.

that carpet though

Linus · Post by **Linus** » Sat Jan 14, 2006 8:23 am

Dragon Puppy - Something like that would be really nice. Definitely keep an eye on the weight the extension arm can handle - my setup probably weighs more than 25 lbs (without the cable management box) and I would want a bit of extra capacity just in case. Also, cables hanging from a "suspended" computer would look pretty strange to me. Despite having that cable box under my screen, I find it's difficult to keep all my USB cables and such tucked out of the way - hopefully moving to bluetooth will help with the clutter.

djnotepad - I'm sure you're going to be surprised to find out that that carpet was absolutely free.

I needed something to cover the floor and knew I wasn't going to live there all that long (I've since moved), so it fit the bill. And it wasn't nearly as awful as I expected - with the log cabin walls and the randomness that's necessary when you share < 400 sq. ft. with someone else, it actually kinda fit:

(note the bike on the wall - you have to be creative when you've got that little space to work with)

Thanks for all the compliments on my system, everyone!

NoizEnvader · Post by **NoizEnvader** » Sat Jan 14, 2006 1:03 pm

I like the carpet. It compliments the log and kinda gives a grassy effect.
O'..., nice job on the PC dude.

Hifriday · Post by **Hifriday** » Thu Mar 23, 2006 10:43 am

Linus wrote:
Hifriday wrote:Linus, excellent work on your Back-of-LCD PC. How did you manage to get your LaScala case to be held up by the LCD? I see a photo of a mount, but it seems quite recessed and a little low on the screen to be the only point of support? BTW what is the size of your LCD?
It was pretty simple, really. The LCD had four VESA mounting holes on the back (check out the 5th picture on the gallery post), which I didn't need since I used the proprietary base mounts underneath (4th picture) to mount it to the cable management box. I removed the feet from the case, drilled holes in the bottom to line up with the VESA holes, and screwed in bolts to hold it on. Then installed the motherboard with cables routed underneath, added drives, etc.

Considerations:

- I lined it up so the front-now-top of the case was just below the little bumps the LCD handle rotates around.
- In theory I could have flipped the handle up so it would be functional, but it's visually distracting.
- At one point I had considered grommets to minimize vibration, but ultimately decided they were unnecessary.
- The one problem with this mounting is that I have to disassemble the PC almost completely to get at the inputs for the LCD. So I was careful to plug in cables for everything I thought I'd need before assembling everything.

The screen is a 17", widescreen-format Planar XP17WSA-01.

Thanks for the kind words!

Thanks for the explanaition.

Linus · Post by **Linus** » Mon Apr 24, 2006 8:19 am

Another update...

I got an M-Audio Transit, which totally eliminated the hiss I had with the motherboard-integrated audio. I also used it to record my fiancee's choir and was happy with the results. Only needs ~1W of power too.

I switched the LCD to run off the PSU's 12V rail, but the ripple in the power made the LCD flicker when below 100% brightness, eliminating any power I might have saved. Went back to using the original brick. See Flickering w/ LCD running off 12V rail - help!.

I decided to un-switch the DVD drive to make it more user-friendly for my fiancee, and 1394 transfer speeds miraculously jumped up to where they should have been. I guess having two devices on the same firewire bridge (even though it claimed to support master and slave) had been the problem all along.

I've given up on the idea of more efficient speakers for now - too many other woodworking projects lined up.

Overall, the machine is working better than ever, and I hope I can stick with it for a couple more years.

jaganath · Post by **jaganath** » Mon Apr 24, 2006 8:46 am

I got an M-Audio Transit, which totally eliminated the hiss I had with the motherboard-integrated audio.

Yeah, I have that problem too. How does it work?

Linus · Post by **Linus** » Mon Apr 24, 2006 12:37 pm

The volume of hiss is basically related to the signal-to-noise ratio of your sound card (or the sound chipset on an integrated motherboard) and the volume setting on your amplifier. Since many DVDs are mastered to have tons of dynamic range (really quiet quiet sections and really loud loud sections), you generally have to raise the volume to be able to hear normal speech. When you do this, it makes hiss more noticeable.

The signal-to-noise ratio is a measurement of how much noise (hiss) there is relative to the input signal (music, movie sound, etc). The combination of lower-quality audio chipsets and the electromagnetically-noisy environment inside a PC case generally mean that onboard audio has a signal-to-noise ratio of around 90dB.

The M-Audio Transit is simply an external, 2-channel sound card that connects through USB. Its signal-to-noise ratio is 104dB. I believe that means that it will have less than a quarter of the hiss at any given volume level.

xinzhitan14 · Post by **xinzhitan14** » Tue Apr 25, 2006 2:28 am

i saw a similar project done in atomic maximum power computing (austrlaian magazine). didnt look as good though . but this is WOW! best mod i've seen for ages now. that screen looks so goood!