Dan's Data letters #7
Publication date: 4-Nov-2002.Last modified 03-Dec-2011.
Quart in a pint pot
I'm trying to set up a home LAN with my main PC, a laptop and a cable modem with Ethernet. Problem is, I have a 5-port switch but not a router. My ISP will charge me if they assign a second IP address. I've looked at some software for proxy servers and such, but all of them seem to require that the cable modem would be hooked up to my PC through USB and a second NIC. For money reasons, this isn't really an option for me. Are there any software routers that can solve my problem?
Jacob
Answer:
There's no easy way to share an Internet connection on a network, using
Windows, without using some kind of gadget with more than one network adapter
in it, unless your actual broadband adapter device (cable "modem" or DSL
"modem"; neither of these devices is actually, technically, a
modem)
has a sharer box built in. In which case the broadband adaptor is the thing
with the couple of network adapters in it, of course.
For any other solution, you need something that can connect to the broadband adapter, and to the network; a basic dedicated sharer box will just have WAN and LAN Ethernet ports on the back. To do it with a computer, you need two network adapters.
Note, however, that there's no reason why you have to use a USB network adapter to connect to your cable modem, if the cable modem is the usual kind with an Ethernet port on it. ISPs prefer USB network adapters because they're easy to install, but unless your ISP uses the network adapter MAC address for authentication (some do, and in that case you need either the network adapter they gave you, or another one with a changeable MAC address), any old network card will let you connect your PC to your cable modem.
Ordinary PCI network cards can be had really cheaply. If you can afford Internet access, I suspect you can scrape together enough for another network card.
Sloooooow storage
Would it be possible to use one of those FlashPath adaptors [mentioned in letters column #3] as a mini hard drive for transporting stuff to mates' places, school etc? I don't have USB, my computer is old, so I can't get one of the little USB things. Or would it be cheaper to buy a Zip drive or something?
P.S. Do you know where I can get plans for a trebuchet so I don't have to buy one?
Matt
Answer:
You could use a FlashPath adapter for carry around storage, but it'd be
pretty painful.
The speed of a FlashPath adapter is limited by the speed of the floppy interface; you're unlikely to manage better than 40 kilobytes per second, and I've seen FlashPaths clocked at only about 30. Reading or writing the whole capacity of a "256Mb" memory card (real formatted capacity maybe 245Mb) will, at 40 kilobytes per second, take more than a hundred minutes. The life of the little lithium batteries would start to become a significant factor, I think.
You could get a used parallel port Zip drive pretty cheaply. A quick ebay.co.nz search (Matt is in New Zealand) turned up various cheap 100Mb drives and less-cheap 250Mb drives available to New Zealand; the shipping would be considerably more than the purchase price of most of them, but you could probably turn up a drive locally by checking out the classified ads.
Parallel port Zip drives can shift more than half a megabyte per second on all but the oldest and crustiest PCs, but the computer'll be pretty much paralysed while they're doing it.
If you're looking for trebuchet plans, you may find this page helpful.
Invisible nodes
I have a WinXP laptop, and a network of Win95, Win98 and WinME computers. I think I've heard that with WinXP, there is a little trouble viewing Win95 machines, and seeing their shared drives, etc. What I want to do is copy files from a Win95 PC to the laptop. A back up to be done once a week. I wanted to automate this using a batch file.
I could do it if I could see the Win95 PC, but I can only see the Win98/ME ones. Which means I would have to copy from Win95 to WinME then WinME to WinXP.
Can you execute a batch file on a remote PC (ie. the WinME machine that can see the Win95 machine) FROM the laptop, to copy the files from the Win95 to the WinME machine, then in the same batch file copy from WinME to the laptop?
Bryce
Answer:
You could use one or another piece of remote control software to do this,
but it'd obviously be preferable to fix the networking problem itself.
If your XP machine can't see your 95 machine, my first guess about why it's happening is that you don't have a local DNS server (most LANs don't), and NetBIOS over TCP/IP is disabled. That'll make Win95-series machines inaccessible to WinXP boxes. All of the 95-series machines (95, 98 and ME) on your network should be invisible to the XP one in this case, of course, but humour me.
To check this, go to Control Panel -> Network Connections on the WinXP machine, right-click the LAN connection and select Properties from the menu. Select TCP/IP and click the Properties button, click the Advanced button, go to the WINS tab, click the Enable NetBIOS over TCP/IP radio button, and OK your way out. Now go outside and meditate for a few minutes, because it may take the XP machine that long to see a Win95/98/ME one. Or just reboot everything in sight; when it's all back up the change should have been made.
If this doesn't help, there are other things you can try.
Update both machines to the latest Windows patch version using Windows Update, and update your network card drivers as well, if you can. This might solve the problem by itself. It doesn't hurt to try.
Make sure you haven't accidentally turned on WinXP's firewall feature in the Properties for the Athlon's LAN connection.
Disable any other firewall software you're running on either machine.
Disable other extra software, like virus checkers. Virus checkers don't usually cause problems like this, but they can.
Also, if any box can't see any other one in Network Neighborhood, that may just be because the invisible computer doesn't have any resources shared. Machines with nothing shared don't show up.
Amnesiac Athlon
Sometimes when I start up my computer the startup message says "Bad CMOS Checksum...", then when I go to BIOS I see all values have been reset to default. This happened twice in the past month and a bit, after I updated the BIOS. It's an Athlon XP 2000 on an MSI KT3 Ultra2 with 512Mb PC2100 ValueRam. I also have a Gigabyte Radeon 8500, using the Catalyst drivers from the ATI site (non-reference, when I downloaded the latest drivers the reference drivers weren't released yet).
Could it be the non-reference drivers giving me problems, because there were no problems at all when I updated my BIOS. Do you have any ideas or suggestions?
Kevin
Answer:
I haven't played with your model of motherboard myself, but if it's like
a couple of its close relatives, then after a BIOS flash you have to press
F1 when you get this message, and hang about for a strangely long time (like,
most of a minute), before you'll get the BIOS setup screen. Then you change
anything that needs changing, save the changes, and you're in business again.
If that doesn't help, though, and the message doesn't come up every time you start the computer, then I'd guess that you need a new CMOS battery. On newer computers, including yours, the CMOS battery is an ordinary lithium button cell, which you can change yourself. The button cell's next to the memory slots on your board.
Mystery washers
Do the little red insulating washers sit on top of or below the motherboard once it is mounted? On the first computer I built I put them on both sides, but I want to get it right this time.
Christopher
Answer:
They're meant to go on top of the board, where you'd expect a screw-washer
to sit, but it doesn't really matter. The purpose of those tough little red washers is not electrical insulation
- because all of the screw-pads on the motherboard are part of its ground plane -
but mechanical protection. The washers slip a little, and that allows the case to
flex and bend slightly without lots of rock-solid fastening points straining
the motherboard at the same time.
The washers also help to protect the board from over-tightened screws, and provide a bit of shake-proofing to stop the screws from slowly backing out.
It's safe not to use the washers at all. It's just slightly safer if you do use them.
LED lighting
Can you run LEDs off of a transformer?
What I need is a bright single light behind an alabaster head, which I intend to sink into a square niche in a brick wall. It will be a tight fit, so I need a light that doesn't generate too much heat. It also needs to run off the mains and be connected to the main light switch. Here in the UK we run off 240V.
What I would like is an even light if possible, if not a small spotlight that picks up the main part of the head from the rear.
I don't know if I can buy such a setup or would have to build one from scratch. I'm a carpenter not a sparks, but hopefully with some guidance I feel I could put something together that would work.
Gary
Answer:
Yes, this can be done. As a non-electrician, you definitely don't want to
roll your own power supply, but you could just buy yourself a "wall wart"
plugpack with an appropriate rating, chop off the barrel plug, and wire
on an LED (or LED array) with an appropriate
current limiting resistor for the LED(s) you're using and the supply voltage
you've got.
Note that non-regulated plugpacks will deliver more than their rated voltage when they're not fully loaded. Get a regulated plugpack instead. If you want something that's made for behind-the-wall installation, one of the transformers made for 12-volt halogen downlights should do you. It'll have a lot more capacity than you'll use, but that ought not to be a problem.
Pointer twiddling
I had a laser pointer one some time ago, and I discovered, way before reading it on Everything2, that it indeed is the perfect cat toy.
Sadly, I broke it long ago, much to the disappointment of my little feline friend.
Now a girl I know has given me hers, but I have an issue. I don't want to use it with the dinky little button batteries: they are weak, expensive and with the intense use I'm planning (diets aren't working, so the cat has to get thinner by burning calories), I'd have to change them way too often. So I was thinking of wiring an external battery (a 3.6V 700MAH rechargeable pack from an old dead cordless phone).
I've tried doing it, and it works. It's very bright (though, of course, not overdriven), and the batteries are likely to last for a long time. But the moment I pressed the button and saw it worked, a thought crossed my mind, and I switched it off immediately. I thought that maybe I need to wire a resistor in series with the battery. I know that LEDs can be safely run from button batteries, but they burn out if you connect them to standard ones. Does this apply to laser pointers, too?
Meltdown
Answer:
Actually, your pointer probably is being driven harder than it was
from three button cells. Those tiny cells aren't meant to power anything
much more demanding than a wristwatch; in laser pointers, they're being
beaten to death, and their output voltage sags quite a lot. That's why tiny
LED flashlights that work from two nominal-three-volt lithium coin cells
in series will blow up if you connect their LED to a six-volt lantern battery; the
lantern battery can deliver six volts to the LED, but the coin cells
can't.
The startup voltage of three fresh button cells, though, is still going to be 4.5 volts or more, for the brief moment before they sag under load. Startup is also when the laser diode will draw the most current from a given voltage, because it hasn't warmed up yet. Most of the bulk, and weight, of the diode modules in laser pointers is the heat sink that's there to stop the diode proper from baking itself.
Add to this the fact that laser diodes that're driven even marginally past their maximum current will die instantly, and it becomes clear that the driver circuitry behind the actual laser diode in the pointer's module is built to keep it safe from 4.5 volts, at unusually high current. So, indeed, 3.6 volts is likely to be fine for arbitrary periods of time. But it's still, probably, more than the module was getting from three button cells, even fresh ones. Hence the high brightness.
What all this means is that you don't need to add anything to protect the laser diode. Laser diodes need some sort of driver circuitry, unless you run them from really well regulated DC supply, or you're happy to keep them well below full power. Even a very brief overcurrent spike will smoke a laser diode.
But because the modules in laser pointers have the driver circuitry built in already, there's nothing more you need to do. In cheap diode modules, the "driver" may indeed just be an in-line resistor; there's often a filter cap across the diode as well, and better diode modules have a full regulator setup, that keeps them nice and bright as the batteries slump down towards zero. In any case, there will be something there, so any reasonably well regulated 3.6 volt DC source (NOT a simple unregulated "3.6 volt" plugpack, whose low-load output will be above 5V...) should be fine.
For tons more info on laser diodes, check this out.
