Mailing List Archive: MythTV: Users

Re: Netbook as low-power combined back-end / front-end?

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roland.sh1000 at gmail

Aug 27, 2012, 8:29 AM

Post #1 of 22 (1115 views)
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Re: Netbook as low-power combined back-end / front-end?

Hello.

Does anyone have any thoughts or experience on running a combined
front/back MythTV setup on a netbook?

My current MythTV setup works perfectly (dual HD tuners, LIRC, etc,
etc)... but most of the hardware is over 10 years old now! I have
no pressing need to "upgrade", and the only reason to "downgrade" to
something newer/slower would be for power/heat/size reasons. I figure
I spend around $140-170 per year in electricity costs to run my
current (old) mythbox.

I was looking at some of the mini-ITX motherboard offerings, and it
occurred to me that I could just use a netbook instead.

Benefits:
* Very small, and portable if needed (travel, etc)
* Battery acts as a built-in UPS (2-4 hours of runtime)
* HD decoding up to 1080p would be possible via a Broadcom Crystal
HD mini-pcie card, or with a NVIDIA ION-based netbook with VDPAU
* Very low power ( <25 watts )
* Compact (could just velcro it to the back of the TV)

I would probably look for a netbook with a broken screen to save some
$$... and I would need to buy the Crystal HD card and a few USB tuners
(or a networked HDHomeRun) to finish it off. But otherwise, I figure
the payoff period would only be about a year.. maybe a year and a half
at most. After that, it would start saving me money - and I'm in this
for the long run.

Has anyone tried this? Any major reasons *not* to do it?

Thanks
- rsh1k
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tylernt at gmail

Aug 27, 2012, 10:47 AM

Post #2 of 22 (1098 views)
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Re: Netbook as low-power combined back-end / front-end? [In reply to]

> Has anyone tried this? Any major reasons *not* to do it?

You will probably get other replies indicating the negative, but this
seems like a fine idea to me. I also run low-power (as far as both
electricity and GHz go) hardware, though I split out my BE and FE.
Running a combined system requires more grunt than split but even so,
a modern dual-core netbook should be up to the task. Some things to
consider:

I don't believe you want CrystalHD. I seem to recall that there are
some Linux driver issues that have not, and may never, be resolved.
VDPAU seems to be the only game in town (from what I understand, VAAPI
is supported in Myth but there are issues there too).

What are you going to use for storage? A netbook is usually pretty
limited space-wise, and recordings like lots of GB. If your netbook
has an SSD, that will be ideal for the OS and DB but you will need a
USB or eSATA external spinning disc for recordings.

Do you want to commflag or transcode? These activities are not suited
to low-power hardware.

Also note that there are already "screenless netbooks" for sale.
Sometimes called net-tops, such as the Acer Revo and Asus Eee Box.
Might be less expensive than a netbook, and may have more room for
internal rather than external spinning discs.

Does your TV have HDMI or VGA inputs? (I ask because a 10-year-old TV
probably doesn't.) If not, you will probably need a new TV -- it's
hard to find FE hardware with analog NTSC outputs these days.
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roland.sh1000 at gmail

Aug 27, 2012, 2:07 PM

Post #3 of 22 (1088 views)
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Re: Netbook as low-power combined back-end / front-end? [In reply to]

On Mon, Aug 27, 2012 at 12:47 PM, Tyler T <tylernt [at] gmail> wrote:
>> Has anyone tried this? Any major reasons *not* to do it?
>
> You will probably get other replies indicating the negative, but this
> seems like a fine idea to me. I also run low-power (as far as both
> electricity and GHz go) hardware, though I split out my BE and FE.
> Running a combined system requires more grunt than split but even so,
> a modern dual-core netbook should be up to the task. Some things to
> consider:
>
> I don't believe you want CrystalHD. I seem to recall that there are
> some Linux driver issues that have not, and may never, be resolved.
> VDPAU seems to be the only game in town (from what I understand, VAAPI
> is supported in Myth but there are issues there too).
>
> What are you going to use for storage? A netbook is usually pretty
> limited space-wise, and recordings like lots of GB. If your netbook
> has an SSD, that will be ideal for the OS and DB but you will need a
> USB or eSATA external spinning disc for recordings.
>
> Do you want to commflag or transcode? These activities are not suited
> to low-power hardware.
>
> Also note that there are already "screenless netbooks" for sale.
> Sometimes called net-tops, such as the Acer Revo and Asus Eee Box.
> Might be less expensive than a netbook, and may have more room for
> internal rather than external spinning discs.
>
> Does your TV have HDMI or VGA inputs? (I ask because a 10-year-old TV
> probably doesn't.) If not, you will probably need a new TV -- it's
> hard to find FE hardware with analog NTSC outputs these days.
> _______________________________________________
> mythtv-users mailing list
> mythtv-users [at] mythtv
> http://www.mythtv.org/mailman/listinfo/mythtv-users

Thanks for the helpful reply.

I did look into the net-tops, as well as the atom and/or ion-based
Mini-ITX equivalents, but found that they were almost all more
expensive than a budget netbook... The Mini-ITX boards would be
nice, as most of them have a PCI slot that I could use for one of my
existing tuners... So I'm still thinking about that. But the
battery is also a pretty big advantage for the netbook. I think the
last UPS I had on my Mythbox was down to an estimated 12 minutes of
runtime after about a year of use... whereas, a netbook with a few
hours of battery would have no problem if I had to unplug it during a
lightning storm or that sort of thing.

I think right now, the used market is pretty good for netbooks.
Between the iPad, the Android tablets, and the UltraBooks & MacBook
Air, the market has largely moved on from the netbook platform to more
"capable" devices... and there are quite a few used netbooks for sale
because of it.

Could you give any details on your low power split backend / frontend
setup? I had always assumed that a single device would be lower
power, as the process scheduling could float back and forth as needed
(transcoding, etc, when the user isn't watching a program, but then
pausing the jobs when video is playing). Do you power down your front
end when it isn't in use?

We flag commercials, but due to some issues with false detections, we
quit transcoding a few years ago. I would probably keep commercial
flagging running, but if a program (or even most of the programs)
didn't make it through the queue before we watched it, it wouldn't be
a big deal.

We used to be on cable, but now we're on OTA only, so it's a fully
digital system. That's part of the reason why my old system has
lasted so long - it was really pushing it to have dual BT848/878
analog tuners and 2x sound cards with flagging and transcoding... so
I upgraded to a trio of Hauppauge PVR-xxx cards... and then with
digital, the CPU load for recording (just dumping the data to disk)
was really low so with a minor graphics card upgrade, HD kind of fell
into place. The system that was at its limits with analog SD was now
perfectly fine for HD. It was pretty neat, actually.

The current "TV" is a 24" LCD via a DVI connection. I would have to
step down to an analog VGA connection for most of the netbooks, but
given the display size and our viewing distances, I don't think it
would be a significant issue. I've been through the hassles of
analog NTSC TV-out, and hope I never have to do that again! :-)

For storage, I would probably have to use a USB drive of some sort. I
have tried using a USB drive before on my current system, and run into
minor bandwidth problems if too many shows are being read/written at
the same time, so I would probably set up MythTV to write to the
internal drive only, with a script to shuffle the recordings to the
external drive when the system is idle.

Thanks again.
- rsh1k
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tylernt at gmail

Aug 27, 2012, 2:53 PM

Post #4 of 22 (1084 views)
Permalink

Re: Netbook as low-power combined back-end / front-end? [In reply to]

> Could you give any details on your low power split backend / frontend
> setup? I had always assumed that a single device would be lower
> power, as the process scheduling could float back and forth as needed
> (transcoding, etc, when the user isn't watching a program, but then
> pausing the jobs when video is playing). Do you power down your front
> end when it isn't in use?

Yes, my FE-only device is an Intel x86 Mini-ITX system with an NVidia
PCI card that's powered off when not in use. Compared to my BE, it's
power-hungry at a couple dozen watts... and requires fans due to my
unwise case selection.

My headless BE is a SheevaPlug, a fanless 1.2Ghz 512MB ARM device with
an external 2.5" 500GB USB HD. Power consumption, including the hard
drive, is something like 6-9 watts.

Note, while Myth 0.23 and 0.24 run on ARM, I haven't tried 0.25 yet.
You may also encounter some anti-ARM sentiment on this list.

> We flag commercials, but due to some issues with false detections, we
> quit transcoding a few years ago. I would probably keep commercial
> flagging running, but if a program (or even most of the programs)
> didn't make it through the queue before we watched it, it wouldn't be
> a big deal.

Yeah, you can still commflag/transcode but if you record a ton of
shows, your CPU may not be able to keep up and your queue will grow
infinitely.

Unless you are transcoding for playback on portable devices, IMHO it's
better to just buy more disk space to hold raw recordings. Disks are
cheap and you buy them once, whereas you pay every month for the
electricity used to transcode.

> The current "TV" is a 24" LCD via a DVI connection. I would have to
> step down to an analog VGA connection for most of the netbooks, but
> given the display size and our viewing distances, I don't think it
> would be a significant issue.

I believe VGA is technically "High-Definition", even though it's
analog. Just keep your cable lengths short, and don't cheap out on a
skinny unshielded cable.

> have tried using a USB drive before on my current system, and run into
> minor bandwidth problems if too many shows are being read/written at

I can record 2 shows from my HDHR and play back a third at the same
time without problems on my 2.5" USB HD. YMMV of course.
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linux at thehobsons

Aug 27, 2012, 11:44 PM

Post #5 of 22 (1083 views)
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Re: Netbook as low-power combined back-end / front-end? [In reply to]

rsh1k wrote:

>But the
>battery is also a pretty big advantage for the netbook. I think the
>last UPS I had on my Mythbox was down to an estimated 12 minutes of
>runtime after about a year of use... whereas, a netbook with a few
>hours of battery would have no problem if I had to unplug it during a
>lightning storm or that sort of thing.

Don't count on the battery being any use. It varies a lot between
battery types and quality of charge management, but some in
particular really don't like not being used regularly. So you may
find that after a few months of being sat there plugged into power,
the battery is dead.

On the other hand, if you pick a system that runs off 12V (as some of
the ION boards do, then in principal you should be able to just hook
this up to a 12V lead acid battery and use a 13.8V supply/battery
charger instead of going with a full UPS. Also, for things like the
mini ITX boards, there are PSUs designed for in-car use that run from
a battery and will auto-shutdown on low battery etc.

Lastly, what sort of climate are you in ? Or more importantly, what
sort of temperatures does your UPS live in ? The VRLA (Vale Regulated
Lead Acid) batteries they use really don't like heat and despite
what's claimed about them they will dry out. If the batteries are
still running, it may be worth prising the cover off to get at the
rubber caps on the cells, and putting a tiny amount of distilled
water in - only a couple of ml, a small syringe is good for that - to
rehydrate them and see if they improve.

--
Simon Hobson

Visit http://www.magpiesnestpublishing.co.uk/ for books by acclaimed
author Gladys Hobson. Novels - poetry - short stories - ideal as
Christmas stocking fillers. Some available as e-books.
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lists at foxhill

Aug 28, 2012, 6:09 AM

Post #6 of 22 (1070 views)
Permalink

Re: Netbook as low-power combined back-end / front-end? [In reply to]

In article
<CABNmk6rGUuqYxuRxsMCz=kNNmRfhagYsZifj6YCDXt3f7j_avw [at] mail>,
Rsh1k wrote:
> Does anyone have any thoughts or experience on running a combined
> front/back MythTV setup on a netbook?

I use Asus Aspire Revo nettops as both front and back ends. These
things are netbook hardware but without the screen and keyboard.

I use the single core for front and dual core for backend, but have no
doubt that a single core would be fine for both.

The combination of vdpau and ion means they are ticking over even when
doing 1080p. ioload is low despite us having four USB DVB-T tuners
connected.

I bought the Linpus version and stuck mythbuntu straight on them. Some
vendors seem to want you to buy Windows as part of a bundle, but I'd
hope you can avoid that.

Ian

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roland.sh1000 at gmail

Aug 28, 2012, 7:38 AM

Post #7 of 22 (1077 views)
Permalink

Re: Netbook as low-power combined back-end / front-end? [In reply to]

On Tue, Aug 28, 2012 at 8:09 AM, Ian Oliver <lists [at] foxhill> wrote:
> Rsh1k wrote:
>> Does anyone have any thoughts or experience on running a combined
>> front/back MythTV setup on a netbook?
>
> I use Asus Aspire Revo nettops as both front and back ends. These
> things are netbook hardware but without the screen and keyboard.
>
> I use the single core for front and dual core for backend, but have no
> doubt that a single core would be fine for both.
>
> The combination of vdpau and ion means they are ticking over even when
> doing 1080p. ioload is low despite us having four USB DVB-T tuners
> connected.
>
> I bought the Linpus version and stuck mythbuntu straight on them. Some
> vendors seem to want you to buy Windows as part of a bundle, but I'd
> hope you can avoid that.
>
> Ian

Thanks Ian.

When you say "but have no doubt that a single core would be fine for
both.", do you mean in regards to your current dual-core backend? ...
or that a single core machine could do both frontend+backend?

Did you ever try running both the front and back end on a single Revo?

- rsh1k
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roland.sh1000 at gmail

Aug 28, 2012, 8:11 AM

Post #8 of 22 (1071 views)
Permalink

Re: Netbook as low-power combined back-end / front-end? [In reply to]

On Mon, Aug 27, 2012 at 4:53 PM, Tyler T <tylernt [at] gmail> wrote:
>
> My headless BE is a SheevaPlug, a fanless 1.2Ghz 512MB ARM device with
> an external 2.5" 500GB USB HD. Power consumption, including the hard
> drive, is something like 6-9 watts.
>
> Note, while Myth 0.23 and 0.24 run on ARM, I haven't tried 0.25 yet.
> You may also encounter some anti-ARM sentiment on this list.

<10 watts! That's impressive!

Do you have any stats on the loads the SheevaPlug runs at? Is that
6-9 watts under load? Is it running high CPU loads all the time
because it is underpowered?

The idle power consumption is the big area I wanted to focus on for my
next build, as we really only record 3-5 shows per day at most. My
current system (Athlon XP) idles at 97 watts and peaks around 160.
:-/ I know I could drop this by 20-30 watts easily by changing
processors within the family, but at that point an Atom would
outperform it for a fraction of the power...

The SheevaPlug sounds cool, and being ARM wouldn't bother me (I'm a
Gentoo user - I'm used to recompiling everything), but I would have to
figure out a better front-end if I went that route and used a split
front/back system. If I used my current system as a front-end, even
for just a few hours a day, it would negate a lot of the power
savings.

> I believe VGA is technically "High-Definition", even though it's
> analog. Just keep your cable lengths short, and don't cheap out on a
> skinny unshielded cable.

Oh yeah, analog is definitely good for "HD" and beyond. CRT
projectors were capable of resolutions substantially higher than "Full
HD" a long time before DVI was available or became common.

- rsh1k
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tylernt at gmail

Aug 28, 2012, 9:14 AM

Post #9 of 22 (1067 views)
Permalink

Re: Netbook as low-power combined back-end / front-end? [In reply to]

>> My headless BE is a SheevaPlug, a fanless 1.2Ghz 512MB ARM device
>
> <10 watts! That's impressive!
>
> Do you have any stats on the loads the SheevaPlug runs at? Is that
> 6-9 watts under load?

The Sheeva by itself idles at about 4W and runs full tilt about 6-7W.
A 2.5" HDD draws another 2-3W or thereabouts.

> Is it running high CPU loads all the time
> because it is underpowered?

The only time the CPU goes to 100% is when Myth does a scheduling run
(once a day or when I schedule a new recording). Recording takes 20%
per stream and playback ~10% or so if I remember right. (My
utilization is higher due to the USB HD, eSATA would be better.)
Otherwise, it idles like any other machine since I don't transcode or
commflag.

Note, this is with 0.23. Someone mentioned that 0.25 requires more CPU
on the BE but I have no hard numbers. I want to upgrade to 0.25 but as
usual, personal life interferes with geek projects! Maybe someone else
here has run 0.25 on ARM and can report.

> The SheevaPlug sounds cool, and being ARM wouldn't bother me

FYI there are other Sheeva-like devices that use the same Kirkwood
CPU, see: http://en.wikipedia.org/wiki/Sheevaplug

> I would have to
> figure out a better front-end if I went that route and used a split
> front/back system.

You could use your existing case and power supply and drop in a new
uATX mobo with a Sempron or Atom. (A while back there was a thread
here about the Sempron that suggested it was reasonably power
efficient.) Replacing the FE's spinning disk with a cheap USB
thumbdrive saves some juice too.

> If I used my current system as a front-end, even
> for just a few hours a day, it would negate a lot of the power
> savings.

True, but at some point there's a crossover where a power-hungry
machine that spends most of it's time off will actually have a lower
*average* power consumption than a power-sipping device that's on all
the time. So, it may pay to run the numbers on various scenarios.
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roland.sh1000 at gmail

Aug 28, 2012, 11:07 AM

Post #10 of 22 (1065 views)
Permalink

Re: Netbook as low-power combined back-end / front-end? [In reply to]

On Tue, Aug 28, 2012 at 1:44 AM, Simon Hobson <linux [at] thehobsons> wrote:
>
> Don't count on the battery being any use. It varies a lot between battery
> types and quality of charge management, but some in particular really don't
> like not being used regularly. So you may find that after a few months of
> being sat there plugged into power, the battery is dead.

Good point. I would have to monitor it over time to see how it was
doing - battery replacement might just be part of a semi-annual
operating cost.

Periodic battery cycling would be pretty easy - you could do something
like putting the computer on an X10 switch module, and setting a cron
job with HEYU to turn the switch off once per month (or whatever
interval is appropriate), and then back on once the battery level is
sufficiently low.

> On the other hand, if you pick a system that runs off 12V (as some of the
> ION boards do, then in principal you should be able to just hook this up to
> a 12V lead acid battery and use a 13.8V supply/battery charger instead of
> going with a full UPS. Also, for things like the mini ITX boards, there are
> PSUs designed for in-car use that run from a battery and will auto-shutdown
> on low battery etc.

Now there's a whole new aspect! A car battery would need to be
outside (hydrogen venting, etc), but could provide a substantial
amount of run time. Plus, it opens up new charging opportunities -
solar, wind, etc - things that with an up-front investment could lower
the annual operating costs even more. Hmm......

> Lastly, what sort of climate are you in ? Or more importantly, what sort of
> temperatures does your UPS live in ? The VRLA (Vale Regulated Lead Acid)
> batteries they use really don't like heat and despite what's claimed about
> them they will dry out. If the batteries are still running, it may be worth
> prising the cover off to get at the rubber caps on the cells, and putting a
> tiny amount of distilled water in - only a couple of ml, a small syringe is
> good for that - to rehydrate them and see if they improve.
>
> --
> Simon Hobson

I was out in the Northwest USA at that point, so I doubt it was heat
or cold that killed it. I didn't check the battery acid levels, but
to be honest, I wasn't particularly thrilled with it even when it was
new. I bought it (a mid-grade APC unit) because our building had a
lot of small power fluctuations... 1/2 second brownouts, that sort of
thing. About once every week and a half, I would come home from work
to find the computer off. With the UPS, the computer would receive a
signal via USB when the battery level was low, and do a controlled
shutdown, preventing any issues with filesystem or database
corruption. It seemed like a good setup.

But in practice, it ended up being rather annoying. At best, when
new, it had about 15 minutes of runtime and would continue on with
only a brief warning squeal to indicate that the power had been
interrupted. But once the batteries started to weaken, it would
trip, estimate that it had <5 minutes of runtime left, and signal the
computer to turn off almost immediately. So even those short power
dips would end up turning the computer off completely. I started
coming home from work and finding the computer off more often than
before. Even turning on a hair dryer in the bathroom would turn off
the TV!

I thought about getting new batteries, and I thought about upgrading
to a bigger UPS. But in the end, I didn't want to spend hundreds of
$$$ and have a massive UPS that was twice the size of my computer, all
sitting on display in the living room. I got rid of that UPS when I
moved...

- rsh1k
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roland.sh1000 at gmail

Aug 28, 2012, 11:25 AM

Post #11 of 22 (1068 views)
Permalink

Re: Netbook as low-power combined back-end / front-end? [In reply to]

On Tue, Aug 28, 2012 at 12:37 PM, Greg Cope <gregcope at gmail.com> wrote:
> On 28 August 2012 17:42, Mark J. Small <msmall at eastlink.ca> wrote:
>>
>> My MBE is a QNAP TS219P NAS box. It's basically a sheevaplug with 3 USB
>> ports, 2 SATA bays and 2 eSATA ports. I need one computer on all the time
>> to run my mail server, print server, file servers, and several other
>> functions.
>> I like it to draw as little power as possible.
>
>
> Can you tell me more - I have considered doing this. What do you record
> (DVB?) Many tunners?
>

Hmm, running a back-end on a NAS is something I hadn't considered...

In addition to Greg's questions:
* Do you do any commercial flagging or transcoding?
* Do you happen to know how much power your system uses?

The QNAP product page lists the power consumption as 5W in sleep mode
and 21W in operation, but that is with 2x 500GB hard drives installed,
and no mention of the brand/model of the drives.

Also, I found this QNAP MythTV step-by-step install guide which looks
to be extremely thorough and well-written:

http://wiki.qnap.com/wiki/How_to_install_MythTV

Is that what you used? Or perhaps you wrote it? (If so, nice work!)

- rsh1k
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linux at thehobsons

Aug 28, 2012, 11:30 AM

Post #12 of 22 (1065 views)
Permalink

Re: Netbook as low-power combined back-end / front-end? [In reply to]

rsh1k wrote:

> > On the other hand, if you pick a system that runs off 12V (as some of the
>> ION boards do, then in principal you should be able to just hook this up to
>> a 12V lead acid battery and use a 13.8V supply/battery charger instead of
>> going with a full UPS. Also, for things like the mini ITX boards, there are
>> PSUs designed for in-car use that run from a battery and will auto-shutdown
>> on low battery etc.
>
>Now there's a whole new aspect! A car battery would need to be
>outside (hydrogen venting, etc), but could provide a substantial
>amount of run time.

You'd want a deep cycle battery - normal car batteries really aren't
suitable as they are designed to provide a lot of power for a short
time (starting) but can't handle deep discharges. Deep cycle (often
called leisure batteries due to their use for 'hotel' loads in
caravans and campers etc) are designed to handle very deep discharge
but are generally not capable of providing the same short power
bursts.
Unless you abuse it, it won't produce a lot of hydrogen so should be
OK as long as it's in a well ventilated area.

>Plus, it opens up new charging opportunities -
>solar, wind, etc - things that with an up-front investment could lower
>the annual operating costs even more. Hmm......

Why do I have visions of the cash registers going wild !

>At best, when
>new, it had about 15 minutes of runtime and would continue on with
>only a brief warning squeal to indicate that the power had been
>interrupted.

Ah, that's probably part of the problem. IMO a lot (most ?) UPS have
too small a battery capacity which means they work the batteries very
hard - quite high discharge rates, plus to get 'good' runtimes I
think manufacturers tend to set them to discharge a bit too much. The
combination can kill batteries fairly quickly - if pulling hard on
the battery till it's voltage is very low, a very slight difference
in cell state can mean you overdo it on one cell. That cell then gets
damaged, reducing it's capacity, so next time it's a bit more out
from the rest, and so it goes.
If you've a 12V battery (6 cells), and discharge it down to 10.5V,
that's nominally 1.75V/cell. If one cell is a bit weak, you could get
that down to (say) 1.5V while the others are still at 1.8V.
Discharging to 1.5V/cell is likely to damage even a good battery.
It's even worse on the big UPS we have at work. That's nominally 120V
(10off 12V blocks in series). By the time you've got that down to
105V, you could have several cells missing altogether and the UPS
wouldn't know. That's why I've got 1/4 ton of scrap batteries at home
waiting till I can have a sort through to see if any will do for 'odd
projects' before they get weighed in at the scrapyard.
I've been looking at forklift (wet) batteries so I can at least top
them up as required - though size, cost, and weight are a factor.

>I thought about getting new batteries, and I thought about upgrading
>to a bigger UPS.

Just bigger batteries would probably have dealt with that.

--
Simon Hobson

Visit http://www.magpiesnestpublishing.co.uk/ for books by acclaimed
author Gladys Hobson. Novels - poetry - short stories - ideal as
Christmas stocking fillers. Some available as e-books.
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roland.sh1000 at gmail

Aug 28, 2012, 12:05 PM

Post #13 of 22 (1061 views)
Permalink

Re: Netbook as low-power combined back-end / front-end? [In reply to]

On Tue, Aug 28, 2012 at 1:30 PM, Simon Hobson <linux at thehobsons.co.uk> wrote:
> rsh1k wrote:
>> Plus, it opens up new charging opportunities -
>> solar, wind, etc - things that with an up-front investment could lower
>> the annual operating costs even more. Hmm......
>
>
> Why do I have visions of the cash registers going wild !
>

Yep, that's a very real concern!

With my current electric bill, I have a modest budget at hand if
averaged out over a few years. But if the payoff period is too long,
then it wouldn't be worth the effort to build something exotic. And
there is a curve to it - where it becomes more and more expensive to
save increasingly smaller amounts of power, and the additional return
for the investment lessens.

... which brings me back to Netbooks and the combined frontend /
backend setup. :-)

- rsh1k
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michael at thewatsonfamily

Aug 29, 2012, 6:35 PM

Post #14 of 22 (1027 views)
Permalink

Re: Netbook as low-power combined back-end / front-end? [In reply to]

On 28/08/2012 4:44 PM, Simon Hobson wrote:
> rsh1k wrote:
>
>> But the
>> battery is also a pretty big advantage for the netbook. I think the
>> last UPS I had on my Mythbox was down to an estimated 12 minutes of
>> runtime after about a year of use... whereas, a netbook with a few
>> hours of battery would have no problem if I had to unplug it during a
>> lightning storm or that sort of thing.
>
> Don't count on the battery being any use. It varies a lot between
> battery types and quality of charge management, but some in particular
> really don't like not being used regularly. So you may find that after
> a few months of being sat there plugged into power, the battery is dead.
>
> On the other hand, if you pick a system that runs off 12V (as some of
> the ION boards do, then in principal you should be able to just hook
> this up to a 12V lead acid battery and use a 13.8V supply/battery
> charger instead of going with a full UPS. Also, for things like the
> mini ITX boards, there are PSUs designed for in-car use that run from
> a battery and will auto-shutdown on low battery etc.
Not exactly an energy efficient way of doing it, unless your battery
charger is smart enough to stop charging when battery is fully charged,
or not charged at all when battery is charged and directly power the
PC. Could be super efficient if you used a solar charger to keep
battery charged, and charge generated was enough to power the machine
during non daylight hours.

>
> Lastly, what sort of climate are you in ? Or more importantly, what
> sort of temperatures does your UPS live in ? The VRLA (Vale Regulated
> Lead Acid) batteries they use really don't like heat and despite
> what's claimed about them they will dry out. If the batteries are
> still running, it may be worth prising the cover off to get at the
> rubber caps on the cells, and putting a tiny amount of distilled water
> in - only a couple of ml, a small syringe is good for that - to
> rehydrate them and see if they improve.
>

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roland.sh1000 at gmail

Aug 29, 2012, 8:36 PM

Post #15 of 22 (1021 views)
Permalink

Re: Netbook as low-power combined back-end / front-end? [In reply to]

On Wed, Aug 29, 2012 at 8:35 PM, Michael Watson
<michael [at] thewatsonfamily> wrote:
> On 28/08/2012 4:44 PM, Simon Hobson wrote:
>>
>> On the other hand, if you pick a system that runs off 12V (as some of the
>> ION boards do, then in principal you should be able to just hook this up to
>> a 12V lead acid battery and use a 13.8V supply/battery charger instead of
>> going with a full UPS. Also, for things like the mini ITX boards, there are
>> PSUs designed for in-car use that run from a battery and will auto-shutdown
>> on low battery etc.
>
> Not exactly an energy efficient way of doing it, unless your battery charger
> is smart enough to stop charging when battery is fully charged, or not
> charged at all when battery is charged and directly power the PC. Could be
> super efficient if you used a solar charger to keep battery charged, and
> charge generated was enough to power the machine during non daylight hours.
>

Even so, I've been looking at the numbers, and I'm not sure going
solar powered in this way would *EVER* pay off, even if your system is
100% off-the-grid with an electricity bill of zero...

Perhaps someone else can double check, but it seems like with a
low-power device (~25 watts), electricity at $0.13 to $0.15 per kWh,
and deep cycle batteries at ~$200 with a life expectancy of 4-8 years
(depending on the depth of cycle), when compared to simply plugging
into the wall, you wouldn't even save enough $$ to pay off the battery
before it needed to be replaced again. And that doesn't include the
startup costs (chargers, solar panels, regulators, etc) - it is purely
just the annual "maintenance" costs.

Is that right? Perhaps a better option is a much smaller and cheaper
battery, as a short-period UPS only (not deep cycled every night), and
using the solar power from a smaller panel purely to offset part of
the daytime power usage?

- rsh1k
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linux at thehobsons

Aug 30, 2012, 12:10 AM

Post #16 of 22 (1020 views)
Permalink

Re: Netbook as low-power combined back-end / front-end? [In reply to]

Michael Watson wrote:

>>On the other hand, if you pick a system that runs off 12V (as some
>>of the ION boards do, then in principal you should be able to just
>>hook this up to a 12V lead acid battery and use a 13.8V
>>supply/battery charger instead of going with a full UPS. Also, for
>>things like the mini ITX boards, there are PSUs designed for in-car
>>use that run from a battery and will auto-shutdown on low battery
>>etc.
>Not exactly an energy efficient way of doing it, unless your battery
>charger is smart enough to stop charging when battery is fully
>charged, or not charged at all when battery is charged and directly
>power the PC. Could be super efficient if you used a solar charger
>to keep battery charged, and charge generated was enough to power
>the machine during non daylight hours.

You would only *EVER* do this with the right sort of charger/PSU. At
it's most simple, this can be a 13.8V (assuming 12V battery and
average temperatures) regulated supply with current limiting (not
overcurrent shutdown). On a fairly flat battery the current limiting
will control the power supplied until the battery reaches a certain
state of charge. After that, the PSU just maintains the fixed voltage
while supplying whatever current the battery requires plus the load.

It's not about efficiency, but about not destroying your battery by
boiling it dry. For a VRLA (aka Sealed Lead Acid, aka Dry-fit) you
can dry them out in a matter of hours with the wrong sort of abusive
overcharging. Wet batteries will take somewhat longer but will still
dry out eventually.

It's not so much a case of "stop charging and power the PC directly"
as simply "float the battery". Connect the load directly to the
charger with the battery in parallel for backup, and use a regulated
charger that will maintain a correct float voltage. The battery will
charge very very slowly at this voltage, but the charger will be
supplying the load directly all the time.

BTW - most intelligent chargers will not work in this situation. They
will see the current being drawn by the load as charging current and
hence the intelligent features just won't work properly - they will
think they are in the bulk charge regime all the time.

Incidentally, this is the basis of a double-conversion UPS which is
used where you want clean regulated power as well as backup. Power
always goes through the AC-DC and DC-AC conversions and so the output
is completely separated from disturbances on the input. The batteries
may be connected directly across the DC link, or there may be a
separate DC-DC converter involved (as is the case with the unit we
have at work).
As you point out, the downside is the extra losses. They are
typically rated at 95%+ efficiency - so a few % of the load gets
added in conversion losses.

--
Simon Hobson

Visit http://www.magpiesnestpublishing.co.uk/ for books by acclaimed
author Gladys Hobson. Novels - poetry - short stories - ideal as
Christmas stocking fillers. Some available as e-books.
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lists at foxhill

Aug 30, 2012, 1:00 AM

Post #17 of 22 (1017 views)
Permalink

Re: Netbook as low-power combined back-end / front-end? [In reply to]

In article <CABNmk6pCV8P1EdoOxZvmbJyHTatc-4M-
hjgmhpmOiekHzbXuiw [at] mail>, Rsh1k wrote:
> Did you ever try running both the front and back end on a single Revo?

Yes, but I didn't try heavily loading it by recording loads of channels
at once while hammering it with multiple frontends.

However, given how much headroom there seems to be, I really can't see
it struggling.

I have four USB tuners which don't have PID filters, so the entire MUX
is hitting the USB bus for them all. My recording disk drive is also on
USB!

Front-end load also doesn't seem to be a challenge once VDPAU is all
working right as the CPU idles even during HD playback.

Ian

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roland.sh1000 at gmail

Aug 30, 2012, 11:55 AM

Post #18 of 22 (995 views)
Permalink

Re: Netbook as low-power combined back-end / front-end? [In reply to]

On Thu, Aug 30, 2012 at 2:07 AM, Terjesen Jens Peder
<Jens.Peder.Terjesen [at] devoteam> wrote:
>
> To me that looks like a less than optimal setup for a UPS.
>
> I have a small UPS with only about 10 - 15 minutes of runtime that works perfectly well for my combined BE/FE.
>
> It is configured to signal the computer to turn off 30 seconds after power loss.
> This prevents short power dips from shutting down the computer.
>
> My BE/FE uses about 30 seconds to shut down, so the UPS is also configured to shut off the power 60 seconds after signaling the computer to shut down.
>
> The BIOS is set to start the computer at return of power.
>
> So short power dips does not influence the BE/FE at all.
> Longer power outages leads to a controlled shutdown, and automatic startup of the BE/FE when power returns.
> This setup also prevents deep discharge of the UPS battery.
>
> I also have one lamp connected to the UPS which gives me 90 seconds emergency light, enough to go fetch a torch.
>
> Jens

Thanks for the detail - that sounds like a great setup, and if I ever
get a UPS again, I will keep this in mind and try to set up something
similar.

With my old setup though, I had a few additional constraints: we kept
the wireless router, cable modem, and cable TV box on the UPS as well.

The cable TV box was on the UPS because any time the power glitched,
it would forget its settings and lose the guide data as well - and it
could take 20+ minutes to fully recover once power was re-applied. So
that was on the UPS to keep it from losing its memory.

The cable modem and wifi router were on the UPS so that we could keep
using the internet on our laptops during the longer power outages.
So once the MythTV box shut down, the cable modem and router would
actually run for a pretty long time (30+ minutes?) without issue.

- rsh1k
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roland.sh1000 at gmail

Aug 30, 2012, 11:58 AM

Post #19 of 22 (1000 views)
Permalink

Re: Netbook as low-power combined back-end / front-end? [In reply to]

On Thu, Aug 30, 2012 at 2:10 AM, Simon Hobson <linux [at] thehobsons> wrote:
>
> BTW - most intelligent chargers will not work in this situation. They will
> see the current being drawn by the load as charging current and hence the
> intelligent features just won't work properly - they will think they are in
> the bulk charge regime all the time.
>
>
> Incidentally, this is the basis of a double-conversion UPS which is used
> where you want clean regulated power as well as backup. Power always goes
> through the AC-DC and DC-AC conversions and so the output is completely
> separated from disturbances on the input. The batteries may be connected
> directly across the DC link, or there may be a separate DC-DC converter
> involved (as is the case with the unit we have at work).
> As you point out, the downside is the extra losses. They are typically rated
> at 95%+ efficiency - so a few % of the load gets added in conversion losses.
> --
> Simon Hobson

Thanks for the detailed reply, Simon! I hadn't even thought about
the computer's load fooling the protection circuits of the charger...

- rsh1k
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roland.sh1000 at gmail

Aug 30, 2012, 12:03 PM

Post #20 of 22 (999 views)
Permalink

Re: Netbook as low-power combined back-end / front-end? [In reply to]

On Thu, Aug 30, 2012 at 3:00 AM, Ian Oliver <lists [at] foxhill> wrote:
>
> I have four USB tuners which don't have PID filters, so the entire MUX
> is hitting the USB bus for them all. My recording disk drive is also on
> USB!
>
> Ian

Hmm... Which tuners do you have? Are there other brands/types that
*do* have PID filters, or is that common across all USB tuners?

Beyond just USB bandwidth (which doesn't seem to be an issue?), I
would suspect that there is a power/efficiency gain by filtering the
programs out on the tuner instead of the system CPU...

- rsh1k
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linux at thehobsons

Aug 30, 2012, 1:06 PM

Post #21 of 22 (994 views)
Permalink

Re: Netbook as low-power combined back-end / front-end? [In reply to]

rsh1k wrote:

>Thanks for the detailed reply, Simon! I hadn't even thought about
>the computer's load fooling the protection circuits of the charger...

Just to clarify, it's not the protection circuits, it's the control circuits.

The "smart" lead acid chargers use a multi-phase charging regime.
Starting from a very flat battery, they will charge in constant
current mode until the battery voltage reaches some specific limit -
typically around 14V for a 12V battery. They then switch to constant
voltage mode while the battery continues to charge - the current will
reduce as the charge state increases.
At some point, the current will drop below the threshold where the
charger determines that the battery is fully charged (the charger
needs to be matched to the size of the battery). The 'charging'
current is no going into electrolysing water into hydrogen and oxygen.
The charger will now switch to float mode (around 13.8V) which will
keep the battery fully charged.
Note: some have more sophisticated regimes, but the above should give
you the gist of what the problem is.

If you have a load running from the battery/charger combination, the
current as sensed by the charger will never drop low enough for it to
detect end of charge. The charger will therefore stay in bulk charge
mode indefinitely and you will "boil" the battery dry.

I'm sure there will be charger/PSU devices around which sense the
battery current separately to the load current - hence they would be
able to properly charge a LA battery while alos supplying a load. I'm
also fairly certain that they'll cost "somewhat more" than a basic
charger !

--
Simon Hobson

Visit http://www.magpiesnestpublishing.co.uk/ for books by acclaimed
author Gladys Hobson. Novels - poetry - short stories - ideal as
Christmas stocking fillers. Some available as e-books.
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dl-mythtv at catspoiler

Sep 20, 2012, 10:47 PM

Post #22 of 22 (710 views)
Permalink

Re: Netbook as low-power combined back-end / front-end? [In reply to]

On 30 Aug, Simon Hobson wrote:

> I'm sure there will be charger/PSU devices around which sense the
> battery current separately to the load current - hence they would be
> able to properly charge a LA battery while alos supplying a load. I'm
> also fairly certain that they'll cost "somewhat more" than a basic
> charger !

Something like this
<http://www.mini-box.com/picoUPS-100-12V-DC-micro-UPS-system-battery-backup-system>
along with a 15-18 V power brick and a 12V SLA will get you battery
backed 12 volts. Add one of these
<http://www.mini-box.com/s.nl/it.A/id.417/.f> for ATX power.

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