Become a fan of Slashdot on Facebook

 



Forgot your password?
typodupeerror

Comment: Re:Even if you go DC, stay at 120V (Score 1) 488

Everything from your wall switches to your wires will cause you never ending problems.

Mechanical wall switches are still rated for DC. Houses USED to be wired for DC a lot. You only have to replace the stuff that was designed after AC was pervasive and wasn't engineered to handle DC.

(I forgot to mention that you'll also have to replace the light dimmers, too, along with most other electronic, rather than mechanical, switches. They usually use a current-zero-crossing turnoff device, and DC won't cross zero unless you force it to do so.)

Even if you replace your wall switches and outlets, your wires will degrade over time and develop holes and other blemishes that will cause a fire.

No they won't - unless they're wet (in which case you have bigger problems than galvanic corrosion). Electromigration at the current densities involved in house wiring is not an issue, nor is insulation breakdown. The wires and fittings will be just fine.

Comment: Re:Even if you go DC, stay at 120V (Score 1) 488

(DANG this stupid touchpad... )

An "inverter", by definition, actually has alternating voltage as a substantial output, or at least somewhere in the circuitry. A switching regulator has a cycling voltage, but it isn't an AC output, or even an AC intermediate.

But they're very similar.

(Also: I was going to mention, above, that the current supplied through the pull-down (or clamp-at-ground) switch is where the extra output current comes from, compensating for the lowered voltage with higher current for similar amounts of power. If the switches, inductors, capacitors, and wiring were all ideal, the driver and sensor circuitry didn't eat any power, and no energy was radiated away as radio noise, efficiency would be 100%.)

Comment: Re:Even if you go DC, stay at 120V (Score 1) 488

A down-stepping DC-DC converter is not an inverter?

Nope. But the pieces of the implementations are similar enough in function that it's close.

A typical DC/DC down converter involves two switches, an inductor, and both input and output filter capacitors, plus control circuitry to sense the output voltage and time the switches. (There may also be a VERY small resistor in series with the inductor to sample the output current if current regulation is necessary, but it's omitted for high efficiency if that's not an issue.) One end of the inductor is hooked to the output cap, the other through the switches to the input cap and to ground.

The pull-up switch is always active (typically a transistor). The control circuitry turns it on and the current in the inductor ramps up, charging the output capacitor at an increasing rate. After a while the pull-up switch is turned off and the pull down switch is turned on. The current through the inductor ramps down, but before it goes through a stop and reverses the pull-up switch is turned back on and the pull-down turned off. The pull-down switch may be a diode, which switches on as needed automatically, but for high efficiency it's usually another transistor, because it has a lower voltage drop and thus is more efficient.

The control circuitry varies the percent of pull-up versus pull-down time to keep the average output voltage at the desired level. The frequency may be controlled or may be allowed to vary somewhat.

So the waveform in the inductor is a sawtooth, and the current never reverses. An "inverter" by definition,

Comment: Re:Even if you go DC, stay at 120V (Score 4, Interesting) 488

(Continuing after brushing the touchpad posted it for me. B-b) ... equipment at that voltage. (Small systems are often 12V due to the availability of 12V appliances.)

But back to inverters:

Current inverter and switching regulator (they're pretty much the same stuff) technology is SO efficient that large PC boards in computing and networking equipment may run the power through as many as THREE DC-DC converters, because you lose less power to heat as losses in the inverters than you would to resistance running it a few inches through a printed circuit board power plane.

So the '"20-40% loss" number seems to me to be utterly bogus.

(Consider this: A Tesla automobile IS AC motors driven by inverters from batteries. A horsepower is almost exactly 750 watts. If they had 20-40% losses in the inverters, how do you keep the car from being on fire after a jackrabbit start? Let alone recover enough power on braking to reuse on acceleration to make a substantial difference?) If ANYBODY knows how to handle inverters it's Tesla. B-) )

Comment: Even if you go DC, stay at 120V (Score 4, Interesting) 488

This is strange. "20 to 40% power loss" seems to be an awfully poor inverter; existing inverters are 4-8 % loss.

Rather than rewire every house in America, wouldn't it make more sense to just design better inverters?

Or just run at 120V DC, as renewable energy systems did (and occasionally still do) before so many appliances were AC-only that it made sense to use an inverter.

Dropping voltage means you have to replace the copper wiring with MUCH HEAVIER wiring - by a square law - to carry a given amount of power with the same loss - and thus wiring heating inside the walls, where it can set the house of fire.

Switching to 120V just means using DC-capable appliances and replacing the breakers (DC is harder to interrupt) and must-be-GFCI outlets (normal GFCI devices use a transformer to sense unbalanced load).

The 48V standard was about having a voltage that was low enough that touching it was typically survivable, so working on or near it is (relatively) safe. The boundary between the hard part and the easy, "low-voltage", part of the electrical code is 50V (BECAUSE of phone companies B-) ). Medium power (>1KW) home Renewable Energy systems tend to be at 48V so much of the wiring falls under the easier part of the code, and because of the availability of

Comment: Not if they think they can get more work out of us (Score 1) 136

by Ungrounded Lightning (#49788985) Attached to: Scientists Reverse Aging In Human Cell Lines

If this works, the monied and in-power will make this as illegal as LSD and heroin.

Not necessarily.

If the anti-aging drug(s) make people healthier, reducing the drain on the government pensions and enabling the government to push the retirement age out over the horizon, so the people will be working and taxed, they might prefer to have the drugs put into use.

Heck, they'd probably add them to the water.

Comment: In particular, NO redundancy. Reliability drops. (Score 5, Informative) 226

Losing data goes with the territory if you're going to use RAID 0.

In particular, RAID 0 combines disks with no redundancy. It's JUST about capacity and speed, striping the data across several drives on several controllers, so it comes at you faster when you read it and gets shoved out faster when you write it. RAID 0 doesn't even have a parity disk to allow you to recover from failure of one drive or loss of one sector.

That means the failure rate is WORSE than that of an individual disk. If any of the combined disks fails, the total array fails.

(Of course it's still worse if a software bug injects additional failures. B-b But don't assume, because "there's a RAID 0 corruption bug", that there is ANY problem with the similarly-named, but utterly distinct, higher-level RAID configurations which are directed toward reliability, rather than ONLY raw speed and capacity.)

Comment: NetUSB=proprietary. Is there an open replacement? (Score 2) 70

It happens I could use remote USB port functionality.

(Right now I want to run, on my laptop, a device that requires a Windows driver and Windows-only software. I have remote access to a Windows platform with the software and driver installed. If I could export a laptop USB port to the Windows machine, it would solve my problem.)

So NetUSB is vulnerable. Is there an open source replacement for it? (Doesn't need to be interworking if there are both a Linux port server and a Windows client-pseudodriver available.)

Comment: Opportunity to detect MITM attacks? (Score 4, Interesting) 71

by Ungrounded Lightning (#49737679) Attached to: 'Logjam' Vulnerability Threatens Encrypted Connections

I skimmed the start of the paper. If I have this right:

  - Essentially all the currently-deployed web servers and modern browsers have the new, much better, encryption.
  - Many current web servers and modern browsers support talking to legacy counterparts that only have the older, "export-grade", crypto, which this attack breaks handily.
  - Such a server/browser pair can be convinced, by a man-in-the-middle who can modify traffic (or perhaps an eavesdropper-in-the-middle who can also inject forged packets) to agree to use the broken crypto - each being fooled into thinking the broken legacy method is the best that's available.
  - When this happens, the browser doesn't mention it - and indicates the connection is secure.

Then they go on to comment that the characteristics of the NSA programs leaked by Snowden look like the NSA already had the paper's crack, or an equivalent, and have been using it regularly for years.

But, with a browser and a web server capable of better encryption technologies, forcing them down to export-grade LEAKS INFORMATION TO THEM that they're being monitored.

So IMHO, rather than JUST disabling the weak crypto, a nice browser feature would be the option for it to pretend it is unpatched and fooled, but put up a BIG, OBVIOUS, indication (like a watermark overlay) that the attack is happening (or it connected to an ancient, vulnerable, server):
  - If only a handful of web sites trip the alarm, either they're using obsolete servers that need upgrading, or their traffic is being monitored by NSA or other spooks.
  - If essentially ALL web sites trip the alarm, the browser user is being monitored by the NSA or other spooks.

The "tap detector" of fictional spy adventures becomes real, at least against this attack.

With this feature, a user under surveillance - by his country's spooks or internal security apparatus, other countries' spooks, identity thieves, corporate espionage operations, or what-have-you, could know he's being monitored, keep quiet about it, lie low for a while and/or find other channels for communication, appear to be squeaky-clean, and waste the tapper's time and resources for months.

Meanwhile, the NSA, or any other spy operation with this capability, would risk exposure to the surveilled time it uses it. A "silent alarm" when this capability is used could do more to rein in improper general surveillance than any amount of legislation and court decisions.

With open source browsers it should be possible to write a plugin to do this. So we need not wait for the browser maintainers to "fix the problem", and government interference with browser providers will fail. This can be done by ANYBODY with the tech savvy to build such a plugin. (Then, if they distribute it, we get into another spy-vs-spy game of "is this plugin really that function, or a sucker trap that does tapping while it purports to detect tapping?" Oops! The source is open...)

Comment: Re:No Chicklets! (Score 1) 147

The inadequately-configurable trackpads, in positions where they detect the palm resting on the laptop (or brushing them) and randomly jump the cursor or highlight whole paragraphs so the next keystroke replaces them, are no help, either.

What do you mean by inadequately configurable? There's usually an option to disable while typing somewhere.

It's there. It's on. Didn't help. Don't know if it's that Ubuntu 14.04 doesn't support it properly on these two machines or if it doesn't do the job I want done.

What I'm looking for is NOT there: A threshold level for touch sensitivity. If you're going to put a BIG touchpad on a laptop's palm rest, you need to either put it where the palms won't brush it, or you need to make it possible to turn down the sensitivity so that a feather-light brushing of the pad doesn't register as a mouse motion or button click.

Two different manufacturers (Lenovo and Toshiba) have used exactly the same layout, and exactly the same hair trigger, non-adjustable, touchpad sensitivity. (Also exactly the same sort of wafer-thin flat tile keys, which is how we got into this digression.)

Comment: No Chicklets! (Score 3, Insightful) 147

The problem I have with current keyboards is not just the short travel and lack of clickyness, but the tiny height of the keys.

Instead of the tall keys with space between them for fingernail clearance, there are these thin squares maybe an eighth of an inch above a solid surface. If I don't keep all my fingernails cut short, when they go past the side of the key they hit the panel and the key doesn't "strike". Letters get dropped. (So I get to pick between typing well and playing the guitar. I pity those who must keyboard for a living but want long nails to maintain their social life.) The short travel means there's little margin for finger variation, so some letters, where my fingers don't depress the keys as far, normally, don't strike, while others, where I support the weight of my hands, do strike when they shouldn't, or strike multiply.

After over a year I haven't been able to adjust. You may have noticed that my spelling has gone to hell as a result: I have to do a lot more correction and sometimes miss fixing things up.

(The inadequately-configurable trackpads, in positions where they detect the palm resting on the laptop (or brushing them) and randomly jump the cursor or highlight whole paragraphs so the next keystroke replaces them, are no help, either.)

On the other hand, when the nails do hit the key, they quickly wear through the top level of black plastic, exposing the backlit transparent light below it. I replaced a laptop about a year ago and after about six months about a half-dozen heavily-used keys had their pretty letters obscured by the giant glow of the scoured away region.

I had been running on older thinkpads and toshibas, with classic keyboard-shaped keys, or at least the little fingertip cup and substantial fingernail clearance. Switching (in a two-dead-laptops-in-two-weeks emergency) to a lenovo z710, then to a company-supplied toshiba s75, both with the stupid "I'm so thin", square, low-travel, no-finger-cup keys has been a disaster.

Comment: Solar offgrid with NiFi battery backup. (Score 1) 403

A solar offgrid (or grid-tied with standalone capabilities) would provide power locally until too much stuff failed.

Lead acid batteries last for several years, recent lithium probably for a couple decades. Nickel-Iron batteries are more lossy, but last for centuries, if provided with water to replace evaporation, potentially decades if they have catalytic fill caps to recombine lost hydrox or, say, a reservoir-based automatic watering system. (If their chemistry has a long-term unavoidable failure mode I'm not aware of it.)

Even with the batteries dead (NiFe or otherwise) the system will have power when the sun is out until at least one panel in every series substring is too degraded, shaded, or smashed to provide adequate power.

Semiconductor controllers might go for a decade to centuries, depending mainly on whether the conductive interconnects of the semiconductors are sized to avoid electromigration at the current levels used and what they're using for large capacitors.

Wind generaors have several moving parts to screw up - how many depends on the design. For a simple homebrew one you have the main bearings, yaw bearing, and tail furling-system bearing. Any one of them failing will take it out. (Even the furling bearing: Once that screws up it doesn't furl right and tears apart in the next storm.) There's also the get-the-power-past-the-yawing mechanism (typically a long cable being twisted and manually "unwound" every few years, or a brush mechanism.) Call it a decade without maintenance at the outside.

So some of 'em may run until a nearby lightning strike fries something.

Comment: Maybe due to misclassifying, esp. the Big-P? (Score 1) 866

by Ungrounded Lightning (#49682577) Attached to: Religious Affiliation Shrinking In the US

I wonder what the numbers would be if "Progressivism" were also counted as a religion, rather than JUST a philosophy or political affilication? B-)

Think about it: It claims to prescribe what behavior is good or bad, generally expects its adherents to take its pronouncements on faith, and has a lot to say against various religions - just like ("other") competing religions do to their opponents.

I could go on with the similarities. But since they include suppression of competing ideas by pretty much any available mechanism (including arbitrary down-moderation, personal attacks, and flame wars), I'd prefer to keep the discussion light.

They're not alone in this, either. (c.f. any of several political philosophies, right, left, libertarian, authoritarian, moderate, ...) But they're my current candidate for the largest not-advertised-as-religion-religion at the moment. B-)

Comment: Re:QoS is hard but necessary (Score 1) 133

My ISP uses an AQM and I can maintain about 10ms of additional latency even when my connection is flooded beyond 100%. ... When I manage my own AQMs on my network, I can maintain 0ms of additional latency, no QoS needed.

Latency is a problem, and as you mention, AQM can deal with it without packet-type distinctions. But it's not the BIG problem when TCP and streams are trying to divide a channel's bandwidth.

That problem is packet loss. TCP imposes it on streams. TCP is HAPPY to accept a little packet loss. Streams get into trouble quickly - and all the workarounds short of QoS packet-class distinctions on the pathway just push the problem around into other aspects (such as delay).

With QoS you can put the drops selectively into, first the TCP flows (which then throttle back), then already-delayed stream packets (which streams no longer need - when TCP could use the equivalent just fine.) In fact you could even give streams strict priority over TCP - provided they're within their bandwidth limit - and avoid dropouts and most of the jitter completely. Streams get the cream and TCP gets the whey, other stuff gets something in between.

A CONS is an object which cares. -- Bernie Greenberg.

Working...