Atomic I/O letters column #141
Originally published 2012, in PC & Tech Authority(in which Atomic magazine is now a section)
Reprinted here May 7, 2013 Last modified 16-Jan-2015.
Wi-Fi-Woe
A while ago you had a letter from someone who couldn't connect more than a few devices to a Wi-Fi router because the router had maximum users set to some very small number.
I have a similar problem, but it's not the same. When I bring my laptop home from work and connect it to my wireless access-point/DSL box/router/etc [model provided, but it turned out to be irrelevant], it can't see the Internet, even if I connect it to the router with an Ethernet cable.
My iPad sees the Internet fine, even if I take it away for days before bringing it back. But unless I haphazardly power-cycle everything, taking my laptop away for eight hours is apparently too much.
Heeeeeelllllp meeeeee!
Leticia
Answer:
It took a little fossicking to figure this one out, but it was all the fault of iTunes.
Or, more specifically, of Apple's "Bonjour" service, which installed along with iTunes on Leticia's laptop. Bonjour provides "zero configuration networking" features; when working properly, it allows a device that's new to a network to see all the stuff on that network, including iPods and iPads and such, with a minimum of fuss.
Unfortunately, though, Bonjour gives devices using it a default TCP/IP gateway of 0.0.0.0, which is guaranteed to not work. The Bonjour-running machine expects that if the network actually has Internet connectivity, a DHCP (Dynamic Host Configuration Protocol) server somewhere on the network will provide a working gateway address. For your average home network, the DHCP server is the broadband-box/router/etc.
When you bring a Windows machine to the network when it hasn't been connected for a while, though, it is likely to get a new DHCP "lease", maybe with a different IP address from the last lease, and all other data the same. Unfortunately, there's some kind of overlap/race-condition problem here, where Bonjour is already running and the computer connects to the network but hasn't yet received new DHCP info. It then ends up mis-connected to some extent, possibly working fine on the local network but convinced its Internet traffic has to go via the nonexistent, never-gonna-work 0.0.0.0.
Bonjour is not actually necessary on most computers that run it - iTunes doesn't really need it. So just setting the Bonjour service it to manual-startup in Computer Management -> Services and then rebooting the computer and the access point should, and in this case did, solve the problem.
Ree! Ree! Ree! Ree!
My kid decided it was a great idea to stab my computer speakers with a texta. Repeatedly, "Psycho" style. The, I believe they're called "drivers", are now a lost cause, but on the plus side I've now seen the inside of an actual voice coil, unwound by little hands attached to a little boy who is now forbidden TV and lollies until he's old enough to vote.
I think the electronics of the speakers are still OK, though. They were pretty nice for no-name speakers - 4-inch woofer, dome tweeter, good enough for music listening not just games. Can the drivers be replaced, or should I just get new speakers?
S.
Answer:
Quick and dirty solution: Read basic specs off back of dead drivers. All you really
care about is the nominal impedance,
which will probably be four or eight ohms. Go to electronics shop with one or both dead
speakers, get new tweeters and woofers of the same impedance and a size that fits, wire
'em up (the
right way round), screw
'em in, and you're done.
If you replace speaker drivers with other random drivers that just happen to fit the holes, though, the speakers will probably end up bass-, or treble- or midrange-heavy, or light. You probably won't actually hurt anything (unless your kid also wrecked the crossover circuitry, which prevents bass going to the tweeter and treble going to the woofer), but it probably won't sound as good.
If you pick drivers whose specification sheets show overlapping frequency ranges and similar efficiency, though, it's possible you'll end up with speakers that sound better than they did when new. This is never going to happen if you replace the drivers in high-quality brand-name speakers, unless the driver specs match really closely. But no-name speakers have cheap drivers, which can often be improved upon.
Office subterfuge
My employer snoops on Web access, and my... sub-optimal... boss yells at anyone who's caught reading Reddit or whatever on company time.
I don't see why it should be a problem as long as I do what I'm meant to do well and on time (which I do, and more), but this argument does not fly with my beloved boss.
So I'd like to be able to encrypt my Web browsing. Not really for personal security or to conceal a porn habit or anything, just so the boss's sycophant in the IT department can't dob on me to the boss about it.
[name withheld]
Answer:
There are browser plug-ins that force
SSL encryption on any
site that supports it (you can kind of do this manually by only going to httpS://...
addresses). You could also use a free or paid remote
proxy (so all of your traffic
goes to the proxy, and from there to whatever you're looking at), or an encrypted proxy
system like Tor,
or set up a Virtual Private Network (VPN).
All of these options make it impractical or impossible for spies in your office to see what data you're sending and receiving (except for the simplest one, SSL, because not all servers support that). A VPN will even prevent local system administrators from seeing where your encrypted data is coming from and going to.
None of these things are actually very useful for you, though, because the mere fact that suddenly a stream of encrypted data is going to and from your computer will probably be taken by your workplace powers-that-be to mean that you're doing something naughty.
And if they don't know what you're doing or where, it's easy for them to accuse you of being a pirate or a child pornographer or something. The only way for you to clear your name then would be to demonstrate that you were only reading Reddit... which would bring you right back to your original problem.
Local IT staff can also just use Terminal Services or VNC or something to snoop on your screen whenever they feel like it.
What you need, if moving to a better workplace is not an option, is an Internet connection entirely separate from the compromised one. Entirely separate from the office network, even, to prevent the screen-snooping attack.
Failing a directional antenna and an Internet-connected friend in line of sight of your office, you could achieve these goals by tethering a smartphone to a separate laptop, and use that connection for your wicked illicit browsing. As long as you don't need a ton of data - reading forums and other such basic Web stuff uses very little bandwidth - you'll be in business, and still employed.
You could even defeat snitches looking over your shoulder if you used one of those sites that camouflages random sites as business software. MSworddit.com makes Reddit look like a Word document, for instance; MSOutlookit makes it look like Outlook, and codereddit makes it look like source code. Hardlywork.in turns Facebook into a spreadsheet. Spreadtweet does the same for Twitter.
Perhaps it's a union rule
I've noticed that many products, like rechargeable flashlights and pumps, will refuse to operate while charging. Other products, like laptops and cellphones, are quite happy to run from the wall socket while also increasing battery charge. Why is this? I see a noticeable price difference, but it's opposite what I'd expect - the cheap products have detection circuits to prevent them from simultaneously charging and operating, while the expensive ones are happy to run in both configurations.
It seems I must be missing something here. So I suppose my question has two parts: why would engineers design in a disabling circuit in the first place? And how does spending more money allow you to fix whatever problem charging causes, without having to disable the device?
David
You can run anything from anything, if you're determined enough.
Answer:
The cheap power supplies generally don't have "detection circuits"; the device they're
powering is just deliberately set up to disconnect the, say, motor of the cordless drill,
whenever the charger's plugged in.
Consider a cheap cordless drill with a low-current wall-wart "overnight" charger. If that charger takes 14 hours to put 1.4 times the amount of energy into the battery as you'll be able to take out again (these are typical numbers for many older rechargeable devices; you always have to put more energy into a battery when you charge it than you'll ever get out of it later), then even if the battery lasted for a whole hour of constant use, the wall-wart would still only be able to deliver a tenth of that constant-use running power.
Since the real constant loaded operating time for a cordless drill is likely to be a lot less than an hour, it's plain that if you made the simplest possible charging circuit with the battery, the charging socket and the (switch-controlled) motor all connected in parallel, then running the drill with the charger plugged in would put far too low a resistance across the charger, load it far too much, and blow it up.
(Chargers of this sort usually have simple current limiting, specifically to prevent people popping fuses in the charger all the time. Plugging the charger into a dead drill and immediately pressing the drill's trigger will in this case, if anything, just make the motor turn very slowly in a sad and grumbling way.)
Modern cordless tools are much more sophisticated than this, but their chargers still
can't deliver enough current to actually run the drill. The solution usually chosen
to avoid this problem is detachable batteries that you slot into a charging station,
or in the case of small rechargeable tools like the little
Dremel Stylus
Mobile phones don't draw a great deal of power or have big batteries, so a simple, cheap plugpack charger can easily charge the phone in a reasonably short period of time, and run it simultaneously. A ten-watt plugpack is a cheap item these days, and more than enough to charge and run a smartphone.
Laptops typically draw less peak power than cordless tools, and also tend to have more powerful AC-adapter power supplies, specifically because laptops have to be able to run from the AC power supply alone with an almost-dead or completely absent battery.
For this reason, there are many laptops that can run from several different power supplies, and many power supplies that can run several different laptops. If you're using a higher-powered laptop with a lower-powered power supply, the power supply may have enough grunt to run the laptop, or charge it while it's asleep or turned off, but not both at once. This situation is a little unusual, but far from unknown.
Laptops also have enough room in their construction budget to include fancy charge-control hardware to handle this sort of setup, built into the batteries and/or the laptop itself. Usually not the power supply, though; modern laptop power supplies are usually pretty "dumb", just delivering a low DC voltage with lots of current capacity, and counting on the laptop to split and regulate it.
This is why $10 eBay car chargers for laptops do actually usually work - they don't set the laptop on fire or anything.
Usually.
