Atomic I/O letters column #104
Originally published 2009, in Atomic: Maximum Power ComputingReprinted here May 4, 2010 Last modified 16-Jan-2015.
Always consider chained 9V batteries
The stars must be out of alignment for me because in the last three weeks, I have purchased from overseas via eBay the following items:
1. Psion Teklogix NetBook
2. Novint Falcon haptic controller...from different sellers, both of which have, coincidentally or by design, arrived WITHOUT a power adapter! So there is a bunch of very exciting bits and pieces just sitting there, which I am unable to use. Very frustrating!
I am left with the challenge of sourcing something which works. The Psion requires a 15.5V, 1.5A output power supply (Watts = V x A, so this is about 24 watts?)
The Novint Falcon power supply is "30 watts, 100V-240V, 50Hz-60Hz".
There appear to be a wide variety of universal power supplies on sale at y'not-particularly-good-friends, DealExtreme, such as their $US25.50-delivered SKU 15249. But it is a "100 watt" PSU.
I am wondering, assuming the plugs fit, whether I could use this potentially with either or both of the above items, or whether I would end up with lumps of burning plastic.
Is it OK to use a PSU which outputs so many more watts that what each device is stated to require?
Larry
When someone asks what your Novint Falcon is, just breezily say "Sex toy!"
Answer:
I wrote
a thing about power-supply substitution a while ago. Sometimes it's easy, sometimes it's not.
One thing you don't need to worry about is a PSU with a higher power rating blowing up your equipment. This is not going to happen, for the same reason why the entire contents of the municipal water reservoir do not blast out of the kitchen tap when you turn it on. (This is also why a car battery with a huge cranking-amp current rating will not electrocute you if you touch the terminals.)
If a power supply is of the old and simple unregulated "linear" type then it will output more than its rated voltage if it's only lightly loaded, and that can kill devices. But all modern computer power supplies, and most plugpacks, are now of the lightweight regulated switchmode type.
The Psion's numbers are in the laptop-PSU range, and yes, a universal laptop power supply like that cheap DealExtreme one will probably do, UNLESS the NetBook has some weird socket on the back rather than a normal barrel plug.
The NetBook's barrel plug actually seems rather small, but if it's too small for any of the plugs that come with the power supply, that problem's solvable. Just find a small plugpack that has the right size of plug, chop it off, and graft it onto the laptop-supply's output wire.
(All usual disclaimers apply about how people who don't know which end of the soldering iron gets hot should not make this their first electronics project.)
You'll also need to know the polarity of the plug. Barrel plugs are usually inside-positive, outside-negative, but you shouldn't stake the life of your gadget on this assumption. This information may be printed or embossed on the back of the NetBook; if not, try contacting one of the numerous NetBook nuts on the Internet to be sure.
The wattage spec on the Novint site is not very useful - it's just the overall maximum power consumption. The Falcon does come with some sort of plugpack, but without knowing what its specs are, you can't replace it.
If you're lucky, input power specs are on the back of the Falcon. If you're not, your best bet may be to just e-mail Novint and ask. I just checked out the downloadable manual and Quick Setup document; neither identifies the plugpack.
Again, a one-size-fits-many laptop PSU or appropriately-specced wall-wart will probably be fine, but plugging stuff in blindly is a bad idea.
It is... the FORBIDDEN cable!
I'm sitting here at work, looking at a USB cable.
On one end of the cable is a USB A plug, the standard oblong one that plugs into computers and hubs.
On the other end of the cable is ANOTHER A plug, exactly the same.
I don't know where my work got this cable from. What is it for? Does it break the USB rules?
S
Answer:
It may violate the USB spec, or may not.
The only plain, "dumb" cables with USB A or (full-sized) B connectors on them that are meant to exist are A-male-to-B-male, for connecting computers to external devices, and A-male-to-A-female, an extension cord. (Which is actually technically against the rules, but which generally works fine as long as you don't daisy-chain more than one extension cord, and/or exceed the five-metre total cable length limit.)
And yet it is the work of ten seconds to find umpteen people selling A-male-to-A-male cables. And even little male-to-male plug adapters, to turn a male-to-female extension cable into an A-male-to-A-male!
If your cable has a lump in the middle or one plug housing bulkier than the other, then it's probably a "link cable" that contains a USB "bridge". That connects two computers to each other in a two-node network, for file transfers, or possibly also Internet sharing, networked games, and so on. If both computers have Ethernet ports then you could just use a crossover network cable, but the USB bridge cable still has a reason to exist.
(Note that FireWire is meant to do this. All you need to connect two FireWire-equipped computers together is an ordinary FireWire cable. You can't do this in Windows any more, though, because as of Windows Vista Microsoft removed the "Direct Cable Connection" feature. USB bridge cables don't use Direct Cable Connection, though; they come with their own special file-transfer software, which may or may not also support normal networking functions like Internet sharing and games.)
An A-male-to-A-male cable without bridge hardware, on the other hand, is forbidden. Connect two PCs with it and the best thing that can happen is nothing. The worst thing involves flames.
Apparently, these cables exist because some very slow learners in the lower end of the peripherals market made some USB devices with A sockets on 'em. Maybe they had a surplus of A sockets. Who knows. But the result was the aberrant creation you hold in your hands.
As a commenters point out in this blog post, there definitely are devices that, for the sake of sheer perversity, have an A socket on them that does the job of a B socket, and there's also USB On-The-Go. USB On-The-Go allows a USB device to act as a host and, for instance, initiate file transfers to or from itself. There are also limited implementations of the same idea that, for instance, let you plug a thumb drive with MP3s on it into your car stereo. This, of course, means you need an A-female socket on the receiving device.
USB On-The-Go doesn't require A-male-to-A-male cables, though. You either plug other devices straight into a USB On-The-Go device, or you use a standard A-male-to-A-female extension lead.
Ping may suffer if you use your neighbour's network
I was looking at Aus PC Market's "pre-made" gaming systems - do they already have network cards to let me connect to a wireless network?
Christopher
Answer:
You're not likely to find many normal "desktop" PC that comes with a Wi-Fi adapter, but it's not
hard to add one.
Most motherboards these days have integrated Ethernet controllers - quite often two of them, at least one of which will be Gigabit-Ethernet-capable - but no wireless network card. This is because, as far as I know, no normal PC motherboards come with a wireless adapter.
Some little small-form-factor boards do come with an integrated wireless adapter, though, because they have few expansion slots in which you could put a wireless card, and they're likely to be used in places like living rooms and reception desks that don't have Ethernet cabling.
(To see a few of those, just search for "wifi" in AusPC's motherboard category page. They've got several boards with integrated wireless at the moment; they're all in the tiny Mini-ITX form factor, which is even smaller than microATX and only has room for one full-sized expansion slot, and often also a laptop-style Mini PCIe slot.)
It's easy to add a wireless adapter to a normal PC, of course. If you don't want anything dangling you can get a PCI or even PCIe Wi-Fi card, but if that doesn't matter you can save a bit of money by getting a USB one instead. (the cheap 'n' cheerful Hong Kong dealers have, of course, a lot of inexpensive options.)
For gaming, it's possible that a USB wireless adapter will add a little to your ping times compared with PCI or PCIe, but in reality the ping difference - even the ping difference between USB Wi-Fi and cabled Ethernet - is unlikely to be noticeable. Modern, 802.11g-or-faster wireless is only bad for gaming if you're getting a lousy signal.
Hey, if Dells are good enough for Stargate Command...
I have a Dell XPS 420, Intel Core 2 Quad Q6600, with 4x1Gb dual-channel 800MHz DDR2 memory. The Nvidia GeForce 8800 GTX 768 PCIe it came with is broken. I think I will replace it with a 1Gb Galaxy GeForce 9800 GT. What do you think?
Nigel
The kids today don't even remember when all Dells were beige, and full of horrible non-standard
components...
Answer:
Yes, that card should work fine. So would a number of other options, though.
I'm leery about installing new and exciting video cards in older brand-name computers, but that's mainly because the power supply can't necessarily deliver enough juice, and in a brand-name (or funny-shaped) computer the PSU can be difficult and/or impractically expensive to replace.
Dell used to be terrible in this respect, using special PSUs with the same connector as a normal ATX PSU, but a different pinout. So anybody who "upgraded" to an ATX PSU barbecued their motherboard.
They're much better now, though; the XPS 420 has a BTX-form-factor motherboard, but like other standard BTX systems, it has a normal ATX PSU.
If the computer originally had an 8800 GTX in it, though, it'll be OK with lots of current graphics cards. A single 8800 GTX can draw a peak of more than 150 watts; the 9800 GT you're considering tops out under 120. A GeForce GTX 280 peaks at well over 200 watts, but the rather-better-value GTX 260 doesn't draw a lot more than your 8800 did.
A Radeon HD 4870 wouldn't draw significantly more than your 8800, either. ATI cards have had a significant price/performance edge over Nvidia products for some time now, and there are several options at or below your wattage budget. A Radeon 5850, for instance, shouldn't strain your PSU, and would give you a substantial video-performance improvement over your old 8800, or the not-a-lot-faster 9800 you're considering. (9800s are considerably cheaper than 5850s, though.)
Note that there's also the GeForce GTS 250, which is a rebadged 9800 GTX. Early 250s were a pure rebadge job, later versions use a bit less power, but aren't any faster. The same goes for the GTS 240; that's a rebadged, lower-power-consumption 9800 GT. (But the inexpensive GT 240, without the S, is a new, if not very fast, card.)
And now, the List of Ways This Could Backfire:
If you're running a 32-bit version of Windows, a graphics card with more memory will create a bigger "hole" in the memory map, which will reduce your accessible system RAM. If you're running 64-bit Windows, the difference should be negligible.
If there's actually nothing wrong with the old graphics card, because the problem is really with the slot or motherboard or PSU or something else, then obviously swapping the card won't help.
If the old card really is dead, but was not the agent of its own demise, then swapping in a new card could just kill that one too. It is possible, though not likely, for a motherboard fault to connect a high-current PSU rail to ground through the graphics card, or do something similarly horrendous.
Oh, and remember to take anti-static precautions when working on your PC. Just because the system starts up after you swap a card without even touching bare chassis metal from time to time doesn't mean you haven't damaged a component, and made the computer less reliable.
