A simple setup I tried with a co-worker of my wife, who can see only about 30% of what is considered normal:
A standard PC with a TV output connected to the largest available TV set (about 82cm 16:9). Windows 2000 was set to a very low resolution (720x480), extra large fonts, high contrast, and a large mouse cursor. Together with the build-in Magnifier (Start -> Accessories -> Accessibility -> Magnifier), the system was usable.
A larger TV set (100 cm 4:3) or a beamer capable of projecting a 200 cm image would have been better, but he said he could work with that setup. Some things that would have disturbed me, like the slightly unsharp picture and the low overall quality of the display did not disturb him at all, simply because he can not see those details. He uses the big part of the screen to find the program, then he used the upper part with the magnifer to read the text on screen. He that that there are better magnifier programs available, but they cost a lot of money.
As a nice side-effect, you can use the TV speakers instead of cheap and noisy PC speakers.
From what I've read about blind people using computers, a lot of problems come from fancy GUIs. So one way to get rid of a lot problems may be to drop the GUI and use a textmode interface instead. My favorite Linux distribution can even be installed by blind people. From there, using standard Linux textmode applications should be no problem.
I think other Linux distributions may also support blind people, especially those who don't start a GUI just to select and copy a few megabytes from the optical drive to the harddrive. *BSD may also be an option, and it is as free (as in beer) as Linux. The last time I touched FreeBSD, it installed like Slackware, in good old textmode.
* A AM or FM tuner tuned to an unused frequency produces noise. The problem is to find a really unused frequency. Under good weather conditions, even a sender far away may be received, thus the signal is no longer truely random.
* All semiconductors produce thermal noise. The base-emitter diode of a germanium PNP transistor, operated in reverse-biasing, is said to produce very much thermal noise. Feed the signal trough an op-amp (uA 741 or similar) so that you get the noise up to line level.
Both ways end in an ADC, for example in the line-in of a soundcard.
* An old TV (without noise cancelling) tuned to an unused frequency is able to produce the same noise as a tuner, but it additionally offers another way to sample noise: It displays random white and black dots that change 50 or 60 times per second. Add some photo diodes and a lot of duct tape and you get a low-speed digital random noise generator.
There is a simple algorithm to improve the quality of the generated noise so that it is more random: Read two bits, B1 and B2, from the raw noise source. If B1 == B2, read again. Return B1. (I don't remember where I read about this algorithm, sorry.)
Tux2000
Use lots of screws and heavy-duty anchors if you don't want your equipment to be moved. Four of them for a laptop-sized box, eight for a tower-sized box, and so on.
Tux2000
To kill "unkillable" Processes, use pskill from sysinternals.com. Also try pslist instad of the taskmanager to list the processes. The taskmanager does not give you all the information you might want to know, like many other tools from Redmond.
Try to kill a whole bunch of suspicious processes at once, so that no part of the malware has a chance to restart another process. Again, pskill can do this.
Boot another system, preferably one that can not execute EXEs, DLLs and so on: Get Knoppix or some other CDROM-based Linux (that is able to write NTFS if you use NTFS for Windows). Use it to browse the WWW, especially to search information about the malware. Use it to delete all executable files (*.EXE, *.DLL, *.OCX,...) of the malware. (Malware registry entries should be harmless if all executables of the malware are deleted.) If you use Knoppix, this is not much harder than deleting files using Windows. You just have to find the right harddrive partition (usually hda1) containing windows and mount it read-write (use the right mouse button on the hdd icon). The real hard job is to find each and every executable of the malware.
Disconnect the network plug / modem / isdn / whatever, switch off WLAN router, etc., before you boot windows to prevent the remaining parts of the malware to re-install itself from the net.
Re-enable network only for the time you run Knoppix on the machine, until you are really, really sure that there are no traces left from the malware.
On a PC, it could be possible to implement some kind of micro-OS, probably fitting on a floppy disk, that contains drivers for firewire and IDE and behaves just like the little chip inside external Firewire-to-IDE cases. It does not need to be very smart: There is no need to know anything about partitions or filesystems, this is the job of the machine mounting the drive via firewire. Accessing a single IDE drive on the primary master connector is easy, just simple port-I/O (unless you want performance). I don't now about low-level firewire access, but AFAIK, it is pretty standardized (OHCI). To find the PCI device with the firewire controller, you can use BIOS services, as well as for video output and keyboard input. All that needs to be done is to translate the firewire protocol for disk access to IDE commands. I think 640 KBytes and x86 real mode should be sufficient for this task. The popular Oxford FW911 chip has just 64 KBytes Flash and a small ARM7 core.
Also from the linked page, right at the top of the page:
The <linux/usb_gadget.h> API makes it easy for peripherals and other devices embedding GNU/Linux system software to act in the USB "device" (slave) role. The drivers implementing and using that API combine to make a useful driver framework for Linux systems that implement USB peripherals.
Many Linux systems will not be able to use it, since they only have PC-style USB Host (master) hardware in a PC, workstation, or server. But when you're putting together embedded Linux systems, a USB peripheral controller option is routine; it's often integrated into processors.
Or short: Your average PC simply does not have the right hardware to use this API.
For a new construction, it is silly to install Cat5. Cat5 limits you to 100 MBit/s, the current standard. Unless you want to re-install all cables within the next five years, you should at least install Cat6, which allows using Gigabit Ethernet (10 and 100 MBit/s still work on that cable). You should install some spare cables, so you can add further wall sockets or replace broken cables without having to open walls. Just install two cables whereever you need one cable. And install cable pairs not only in one corner of each room, use two to four different places, depending on the size of the room. Unlike conventional Ethernet, Gigabit Ethernet uses all four pairs in the cable, so there are no longer unused pairs in the cable that could be used for a second device or as a replacement pair. You should use tubes so you can replace the cables later. You should have a small room with a little 19 inch rack for servers, switches, and patch panels. Your initial plan should not fill more than 50% of the rack.
By the way: It is no problem to use Cat5, Cat5e, Cat6 or even Cat7 for ISDN or analoge telephone lines, and you should do this. It gives you a lot more flexibility. There are even solutions to drive video and audio signals over Cat5 or better, and depending on the quality of the cable, it should be possible to drive antenna or cable tv signals over Cat6 or Cat7, using an impedance adapter on each end.
I say design the whole damn thing to run off 12V DC. You can use a voltage divider (a simple circuit made with a network resistors in parallel) internally to create +/-5V and +/-3.3V. Simply provide a round, 2 contact plug that says "12 VDC In".
No, you don't want to use a voltage divider. A voltage divider works fine as long as the load connected to the voltage divider has a much higher resistance than the voltage divider resistors. If you want to drain 5V @ 2A from a voltage divider, you effectively connect a 2.5 Ohm resistor in parallel to your voltage divider. This may still work (with a really hot milli-Ohm voltage divider) as long as you need constantly 2A. But computers are not constant current sinks, they have a varying need for current. If you know Ohm's law, you can easily calculate that the voltage will not be constant in that case.
Go for a voltage regulator, preferably a switched one with offers a better efficiency factor than a linear voltage regulator. These are standard in all norebooks, plus they run from an unregulated(!) DC input of 8V to 20V.
The tricky part is the hard drives. They really want to see +/- 12V. I'm pretty sure, and please, someone correct me, that you could actually provide that by providing the +12V leg of the system with the straight power, and simply reversing the polarity of power coming in for the -12V. That is assuming that you can't find a hard drive that operates at 5V. I'm too lazy to research it.
Desktop harddisks use +12V and +5V, the same applies to optical drives and floppies. Laptop harddisks, optical drives and floppies use +5V only, some newer ones use +3.3V. No component in a PC of the last few years uses -5V or -12V, except the RS232 ports that use -12V for signalising. The new standard for ATX power connectors even change the only pin supplying -5V to "reserved" (i.e. unused). There are many chips for RS232 that generate the required positive and negative voltages (with a low current) from a single +5V (MAX232) or even +3.3V (MAX233) line, so even -12V will soon be obsolete.
Couple that with a diode to prevent the system from being damaged by reversed wires, and a big Cap to handle power dips and surges and you will have a Joe-proof computer.
You don't need diodes if you use a connector that can't be reversed. You don't need a capacitor if that connector has a lockable connection (like XLR). Remember that a diode between the external power supply and the internal voltage regulator drops about 0.6V (0.2V for a schottky diode), and the entire current for the system (up to 4A in current laptops) flows through this diode. So it is heated with 0.6V * 4A = 2.4 W that need to be cooled or it will die. It is possible to design a DC switched power supply that can stand reversed polarity, because it simply does not start with reversed polarity, so there is really no need for a diode.
Try to buy a professional printer. Not those with a big bright "professional" label, tools with such labels aren't "professional". Look at the vendor web pages what printers they offer for business ("enterprise") use. They may be ugly, big and expensive, but they offer better quality and longer a lifespan than those toys sold for SOHO use.
Search for a printer with Postscript support. It makes life easy with any OS (*BSD, Linux, MacOS, MacOS X, and even DOS and Windows can print on Postscript printers), and at the same time you can be sure that the printer has a real CPU and not just a chip that does nothing more interfacing the printer's hardware to a Windows-only "GDI" driver. Make sure the printer has some RAM, 8 MBytes is the absolute minimum, better try to get 32 MBytes.
The printer should have a build-in (ethernet) print server, or at least an external print server from the same manufacturer. I've seen HP printers refusing to do more than the absolute minimum work (unidirectional printing without any status reporting) until they have been connected to an HP print server. The reason for the print server: Ethernet does not die, it justs becomes faster. Parallel ports become more and more rare these days, many laptops already omit them. USB will some day be as obsolete as ISA is today. USB limits you to 2m printer cable, a parallel port may work with up to 5m, but ethernet gives you 100m. Plus you can share the printer with as many computers as you like, without the need to power up a dedicated computer for printing. And as a nice extra: With a WLAN access point or WLAN router, you can even print wireless.
My Hardware: HP Laserjet 1200N, a LJ1200 with 16 MB RAM plus an external ethernet to USB print server in the box. Yes, it's a SOHO toy (with Postscript support), and I would prefer a LJ 4000/4050/4100, but I got it for free. I've printed 1500 pages without any problems, from Windows, Linux and MacOS 9.
... but make sure you don't run VNC on an unsecured machine connected to the internet. At least close all other ports and tunnel VNC over ssh (see google for how this is done). You don't want a bunch of script kiddies to take over the PC, do you?
Some ATMs are designed for outdoor usage, the "worst case" ATM I saw was simply mounted into a wall with absolutly no wheather shielding. It had to stand rain, snow, storm, and hail. Other Public Terminals are comparable. Both have to withstand really dirty fingers, cola, coffee, often also wheather, and of course vandalism.
On the inside, you often find an ancient major-brand PC, and in case of the ATM, some special hardware to dispose money. Exchanging or upgrading the PC or running some kind of terminal software on it (TightVNC, Terminal Services Client, X11 Server,...) should be no real problem, the special hardware can be removed, and you end up with a heavy duty PC box with at least a build-in, shielded screen. With a public internet terminal, you also have a "bullet-proof" keyboard and a mouse replacement. Otherwise, add a sealed ("waterproof") keyboard and a cheap optical mouse. Try to replace the tiny PS/2 style connectors with some better, heavy duty connectors (4 pin XLR is the best, DIN-5 or DSUB9 should also do the job), using two adapter cables inside the box and new connectors on keyboard and mouse.
For the software side, try not to store anything on that box, but place all your documents on a fileserver in a more friendly environment. Small NAS boxes are available for around 200 US$. Have a replacement harddisk and an up-to-date image of the system available. Even better, avoid the entire harddisk and boot from the network (search terms: PXE, EtherBoot) or a small compact flash card with an IDE adapter.
Do you remember the story of NASA searching i8086 CPUs for their space shuttles just two years ago? There are other stories, I remember some companies paying a lot of money for ancient Toshiba 386 laptops that was the only computer certified to "remote control" a certian pacemaker. A re-certification of a new system would have cost much more than buying a few 386 laptops at pentium-class prices.
Some systems (not only NASA shuttles) are designed around a randomly selected CPU, and they run with software that needs the exact behaviour and timing of that special CPU. Say hello to the world of embedded systems.
This message from intel is just a warning for designers of embedded systems that there will be a day when there is no spare P-II left.
I don't know what's wrong with dnsmasq+exim (and I'm too lazy to search google), but dnsmasq is under very active development and has fixed a lot of bugs, some esotheric, some really nasty. Details are in the changelog. Perhaps the trouble with exim has already been solved. You may want to give dnsmasq a second chance.;-)
I still use sendmail from Slackware 8 in my LAN, it just works, with both my now disabled bind and with dnsmasq 2.something. I want to change to some other mailer, but I've not yet found the time to learn and install exim or postfix.
For small networks, I recommend using dnsmasq. It's a combined DHCP server and DNS server/proxy intended for use on a masquerading gateway that can run nearly without any configuration. Add your mac addresses to/etc/ethers for fixed IP adresses, add your hostnames to/etc/hosts, finito. There is no need to fiddle with to big servers (bind and ISC dhcpd). I use it on my (heavily modified) WRT54G with about 10 to 20 systems without any problems.
[...] buy a Linksys WRT54G, flash the firmware, and have a VPN solution [...] plus a bonus WAP.
Hmm, if someone want to protect his data in his network(s), he surely does not want a WAP in that network. Or if he wants a WAP, he has not yet been properly educated. (Well, there may be some reason to run a VPN over WLAN, but you do not want unprotected WLAN.)
I develop and code a web-based database application, that is installed on a dedicated server at our client's sites. In most cases, we also install some kind of remote access software for maintainance. We access this software via Modem or ISDN with or without callback, VPN or special firewall configurations via internet. Some clients even expose the server to the internet.
Some clients (usually smaller companies and non-profit organisations) have very low security standards and trust us to be "the good ones", so our software is installed on a server directly inside their LAN, without further security measures. Often, we also have remote access to the server. No one seems to care that we could access their entire network. We don't, not even for fun, but we could.
Some clients (usually banks, insurances, and telecommunication companies) are really paranoid, they do not allow any kind of remote access, and the server is placed behind a separate firewall. All maintainance has to be done from the console or from a special workstation inside their network.
Most clients put the server into their DMZ and provide remote access to the server via VPN or dial-up, often combined with some kind of token (most times from RSA). In this setup, the database runs either locally on the application server or a special firewall rule allows access to a "big" database.
In very few cases, we install the application server in our DMZ. This happens if the client does not have a proper infrastructure or if two clients need parallel access to the same data. The client accesses the application via internet, maintainance is done through our internal firewall.
Our big advantage is that we need only one TCP port (80 for http or 443 for https) with one protocol (HTTP), this is rarely a problem for any kind of firewall or network admin. For remote access, we can use different software with different requirements, depending on the wishes of the clients. SMTP, POP3 and IMAP4 can be handled very similar. Other server applications can be much harder, even such "simple" things like a Windows fileserver needs various TCP and UDP ports, and firewalling such applications can be a major PITA. Even FTP needs at least two ports and contains IP addresses inside the data packages, but either passive mode or a smart firewall can help firewalling FTP.
So, if you "just" need some software based on well-known internet standard protocols, a dedicated server behind a firewall should do the trick. If the vendor wants remote access, add a protected (i.e. callback + token) modem or ISDN line. If you need propritary software, maybe even in a non-IP environment, the things become harder. You may even need to build your own firewall or proxy, perhaps based on Linux or *BSD.
My tips from my experiences - or: how I prefer to work.
Bright Workspace:
How: At home, I light my workspace with a 40W fluorescent ring lamp (made by Philips, type "TLE 40W/25") with a cold light color. Its advantage is that it illuminates the entire room very homogenous. The disadvantage is that food looks ugly, especially meat. I work on a white desk.
At work, I have to live with two bands of linear flourescent lamps (22W each, I guess) each, shared for four tables. They produce enough light, but it is not as homogenous as the ring lamp. The desk at work has a light wood decor. Not optimal, but it works, because it is usually burried under heaps of paper. Why: The low contrast between monitor and work environment reduces stress for the eyes. Try it: find a dark room and look onto a bright PC display (TFT or CRT) for a few minutes. I can't stand it longer than a few minutes.
Proper Monitor:
I prefer high quality CRTs. I own and use several Eizo Flexscans, 17 and 21 inches, and I recently ordered a new 17 inch Eizo Flexscan for my work place, even if (or perhaps because) the company policy is to buy low-cost TFTs. Sure, CRTs are large and ugly, and they need a lot of energy. But IMHO, the image on a good CRT is smoother than on a TFT. There is no color problem when you look from the side onto the CRT. CRTs don't have to interpolate the image to display different resolutions.
Proper Resolution and Refresh Rate:
For TFTs, look into the manual, but usually, you have to use 60 Hz refresh rate for best quality. And you have to use the native resolution of the display (see manual), or else it will interpolate the image or does not use the entire screen. For CRTs, adjust the refresh rate to something between 85 Hz and 120 Hz. Depending on the light, there may be some flicker effects if the frequency of your light's power supply and the refresh rate are small integer multiples of a common base frequency: 50 Hz power supply for the light and 75 Hz refresh rate (2 : 3) cause massive flicker on my monitors, followed by a headache after a few minutes. Setting the refresh rate to 85 Hz removes this effect. Use the resolution recommended by the manufacturer of the monitor, or the next smaller resolution. Do not use the theoretical maximum resolution from the data sheet or the catalogue, this is the resolution that just does not kill the monitor, but it is not the optimum resolution.
I recommend to use not more than 1024 x 768 on a 17 inch CRT / 15 inch TFT. Buy a larger monitor if you permanently need higher resolutions.
Proper Setup
Make sure there are no reflections on the monitor (e.g. sun, window, lamps).
Place the monitor directly on the desk, don't place it on a desktop case or a monitor stand. Make sure you do not have to look up to see the entire screen. Many monitor manuals recommend to adjust the monitor so that you look onto the center of the CRT / TFT, but I prefer to look from above onto the monitor, with my eyes just above the case, in a distance of 1.5 times the monitor diameter.
Use high quality cables (preferably BNC). Cheap cables can cause massive interferences, visible as vertical or horizontal bars, blurred fonts, and so on. The cable has to transport high frequency signals (100 MHz and more), that just does not work with a cable made from clotheslines and bell wire. Don't use extension cords for the video signal, use a longer cable or even better: Move your equipment. Each additional connector degenerates the signal.
Use a good graphics adapter. The output filters found on cheap graphics adapter often degenerate the signal at high resolutions and refresh rates until it is unusable. Major brands usually have good filters, cheap clones, onboard junk (with shared memory), and many laptops often have poor filters.
Avoid console switches (KVM), at least for your main monitor. Most KVMs degenerate the video signal or can't work with the optimum refr
Wrong! Dangerously wrong! Do you want someone to be killed by blindly believing this statement?
A switching PSU is dangerous after unplugging the mains for quite a while. You know that:
Sure, there are big capacitors in there, but after a couple of days, even these have trickled to a full discharge.
The important statement is that it takes a lot of time for the capacitors do discharge. And you don't really want an amateur to fiddle with a switching PSU, without knowing about dangerous parts and without proper equipment (at least an isolating transformer and properly isolated tools). At least I don't want it.
So, please kids, don't try this at home. Don't open any equipment that operates at more than 40 volts or generates more than 40 volts. Don't try to repair that equipment unless you want a Darwin award or you have had a proper training.
My (expensive) USB flash stick died a few weeks ago, after two years of usage. I could still read it, but it refused to be written. Gladly, my vendor gave me a new USB stick for free, but this is definetly not the media I want to store my important files on.
My backup is an external firewire case with a large ATA harddisk, combined with a script that writes all modifications in the main RAID-1 filesystem to the backup harddisk. Tape drives are too expensive, and tapes wear out rapidly. Burning complete backups to DVD-R(W) or CD-R(W) takes way too long, and you need a huge pile of discs to backup just a few ten Gigabytes. The downside is that there is yet another fragile harddisk that may die some day. My hope is that not all harddisks die at the same moment. That's why the backup harddisk is usually disconnected from both power and firewire.
I assume your friend uses an OS that supports using more than one mouse in parallel, i.e. Linux, MacOS X or recent versions of Windows (98 or newer, 2000 or newer). I assume that your friend can use at least one foot (or hand) to operate a foot switch.
You need two mice, one for the cursor movement and one for the buttons.
The "buttons" mouse should be a cheap one, preferably with a removeable ball and a long cable. The entire ball mechanics is no longer needed, just the electronics. You need one, two or three simple foot switches (temporary contact, i.e. contact is closed only when the foot switch is pressed down). Connect the two contacts of each foot switch in parallel to each mouse button. If your friend needs only one foot switch, you may hide the electronics of the mouse inside the foot switch. If your friend needs more than one switch, drilling some holes into the mouse case for headphone jacks (one for each foot switch) may be a good idea.
The "cursor" mouse can be nearly any mouse. If your friend can't move the mouse without accidentally clicking some buttons, open the mouse and cut off the little plastic pieces below the mouse buttons that press the switches on the electronics board.
Now your friend can use the "cursor" mouse to move the cursor, and the foot switch(es) to click. Even drag and drop should be possible, he just has leave one foot on the foot switch.
I admit this idea may look strange, but I think it is quite usable. Many secretaries use foot switches to control dictation machines. Think about driving a car. How do you accelerate? How do you stop a car? Planes are even directed with the pilot's feet, at least while they are not flying.
... just pay the repair folks. They (should) know what they do.
The other way: get a repair manual, lots of small tools, and a replacement drive that fits mechanically and electrically into the laptop. Fiddle with some of the tools and your laptop. Result: You have a heap of screws, wires, plastic parts, and strange matter you have never seen before, your laptop is now really broken, the new harddrive has not survived, and you have spent more money than the repair folks demanded. Add a large ammount of super glue to the heap,sell it as piece of modern art on ebay, buy a new laptop and make sure it is repaired by experts next time.
A kid with vision disability can participate with his classmates in geography, but he might need some help. Help which, I should note, is required by law and for good reason.
That help may be a technical device, like a magnifier, a screen reader, a braille printer, a blindman's stick, an extra large book, a tactile map or globe, or some other "gadget". But as some others have already stated, this may lead to isolation. I don't want to say anything bad about this stuff, I'm glad it exists. But there is another way to help:
TEAMWORK, especially of the students.
It means more work for the teacher: He has to develop tasks that can be solved best by a team, not by a lone warrior. He may have to fight with authorities to be allowed to go an unusual way. He may have to fight with students that want their old multiple choice tests back. But it helps the students learning to work as a team of specialists. I'm sure this helps all students more to get through their lives than to know the Capitol of the South American country to the west of Surinam.
I prefer to work as a lone warrior, but I need my team to compensate my deficits (handling clients, getting the newest rumors, handling company politics). I work this way since five years, I really like it, and I produce excellent results. I learned teamwork at university, way too late. During the last five years, there were some short experiences when the whole team worked like a single mind distributed over a few bodies to avert a huge damage, and these moments were the best. Knowing the Capitol of the South American country to the west of Surinam wouldn't have helped a little bit, but knowing how to work as a team did.
By the way: I know my (handicapped) wife from my alternative civilian service in a sheltered workshop, and I know the problems with the integration of handicapped people. It is a permanent fight and requires a lot of energy from all people involved, especially the parents.
I once used an ancient Apple Laserwriter 12/600. It produced a feelable amount of toner on the print-outs (I guess 0.25 to 0.5 mm), much more than any other laser printer I've seen. I don't know if it was adjusted improperly or if it was using the wrong toner, or if it just behaves this way. I'm not blind, and I'm not trained to read braille, but I'm sure that a map printed on that old printer would have been feelable.
I think that a solid ink printer could do the same job, perhaps even better. A printer driver for the Apple Laserwriter 12/600 is available at least in Win2000, Win98, Linux and Mac OS, as it is just a plain postscript printer. I don't know how about solid ink printer drivers.
Slashdot Mirror
A simple setup I tried with a co-worker of my wife, who can see only about 30% of what is considered normal:
A standard PC with a TV output connected to the largest available TV set (about 82cm 16:9). Windows 2000 was set to a very low resolution (720x480), extra large fonts, high contrast, and a large mouse cursor. Together with the build-in Magnifier (Start -> Accessories -> Accessibility -> Magnifier), the system was usable.
A larger TV set (100 cm 4:3) or a beamer capable of projecting a 200 cm image would have been better, but he said he could work with that setup. Some things that would have disturbed me, like the slightly unsharp picture and the low overall quality of the display did not disturb him at all, simply because he can not see those details. He uses the big part of the screen to find the program, then he used the upper part with the magnifer to read the text on screen. He that that there are better magnifier programs available, but they cost a lot of money.
As a nice side-effect, you can use the TV speakers instead of cheap and noisy PC speakers.
Tux2000
From what I've read about blind people using computers, a lot of problems come from fancy GUIs. So one way to get rid of a lot problems may be to drop the GUI and use a textmode interface instead. My favorite Linux distribution can even be installed by blind people. From there, using standard Linux textmode applications should be no problem.
I think other Linux distributions may also support blind people, especially those who don't start a GUI just to select and copy a few megabytes from the optical drive to the harddrive. *BSD may also be an option, and it is as free (as in beer) as Linux. The last time I touched FreeBSD, it installed like Slackware, in good old textmode.
Tux2000
* A AM or FM tuner tuned to an unused frequency produces noise. The problem is to find a really unused frequency. Under good weather conditions, even a sender far away may be received, thus the signal is no longer truely random. * All semiconductors produce thermal noise. The base-emitter diode of a germanium PNP transistor, operated in reverse-biasing, is said to produce very much thermal noise. Feed the signal trough an op-amp (uA 741 or similar) so that you get the noise up to line level. Both ways end in an ADC, for example in the line-in of a soundcard. * An old TV (without noise cancelling) tuned to an unused frequency is able to produce the same noise as a tuner, but it additionally offers another way to sample noise: It displays random white and black dots that change 50 or 60 times per second. Add some photo diodes and a lot of duct tape and you get a low-speed digital random noise generator. There is a simple algorithm to improve the quality of the generated noise so that it is more random: Read two bits, B1 and B2, from the raw noise source. If B1 == B2, read again. Return B1. (I don't remember where I read about this algorithm, sorry.) Tux2000
Use lots of screws and heavy-duty anchors if you don't want your equipment to be moved. Four of them for a laptop-sized box, eight for a tower-sized box, and so on. Tux2000
- To kill "unkillable" Processes, use pskill from sysinternals.com. Also try pslist instad of the taskmanager to list the processes. The taskmanager does not give you all the information you might want to know, like many other tools from Redmond.
- Try to kill a whole bunch of suspicious processes at once, so that no part of the malware has a chance to restart another process. Again, pskill can do this.
- Boot another system, preferably one that can not execute EXEs, DLLs and so on: Get Knoppix or some other CDROM-based Linux (that is able to write NTFS if you use NTFS for Windows). Use it to browse the WWW, especially to search information about the malware. Use it to delete all executable files (*.EXE, *.DLL, *.OCX,
...) of the malware. (Malware registry entries should be harmless if all executables of the malware are deleted.) If you use Knoppix, this is not much harder than deleting files using Windows. You just have to find the right harddrive partition (usually hda1) containing windows and mount it read-write (use the right mouse button on the hdd icon). The real hard job is to find each and every executable of the malware.
- Disconnect the network plug / modem / isdn / whatever, switch off WLAN router, etc., before you boot windows to prevent the remaining parts of the malware to re-install itself from the net.
- Re-enable network only for the time you run Knoppix on the machine, until you are really, really sure that there are no traces left from the malware.
Tux2000Get an assistant (some first-year student), and pay him a few bucks for doing your job.
Tux2000
On a PC, it could be possible to implement some kind of micro-OS, probably fitting on a floppy disk, that contains drivers for firewire and IDE and behaves just like the little chip inside external Firewire-to-IDE cases. It does not need to be very smart: There is no need to know anything about partitions or filesystems, this is the job of the machine mounting the drive via firewire. Accessing a single IDE drive on the primary master connector is easy, just simple port-I/O (unless you want performance). I don't now about low-level firewire access, but AFAIK, it is pretty standardized (OHCI). To find the PCI device with the firewire controller, you can use BIOS services, as well as for video output and keyboard input. All that needs to be done is to translate the firewire protocol for disk access to IDE commands. I think 640 KBytes and x86 real mode should be sufficient for this task. The popular Oxford FW911 chip has just 64 KBytes Flash and a small ARM7 core.
Tux2000
Also from the linked page, right at the top of the page:
Or short: Your average PC simply does not have the right hardware to use this API.
Tux2000
For a new construction, it is silly to install Cat5. Cat5 limits you to 100 MBit/s, the current standard. Unless you want to re-install all cables within the next five years, you should at least install Cat6, which allows using Gigabit Ethernet (10 and 100 MBit/s still work on that cable). You should install some spare cables, so you can add further wall sockets or replace broken cables without having to open walls. Just install two cables whereever you need one cable. And install cable pairs not only in one corner of each room, use two to four different places, depending on the size of the room. Unlike conventional Ethernet, Gigabit Ethernet uses all four pairs in the cable, so there are no longer unused pairs in the cable that could be used for a second device or as a replacement pair. You should use tubes so you can replace the cables later. You should have a small room with a little 19 inch rack for servers, switches, and patch panels. Your initial plan should not fill more than 50% of the rack.
For a lot more of good tips, search for "structured cabling".
By the way: It is no problem to use Cat5, Cat5e, Cat6 or even Cat7 for ISDN or analoge telephone lines, and you should do this. It gives you a lot more flexibility. There are even solutions to drive video and audio signals over Cat5 or better, and depending on the quality of the cable, it should be possible to drive antenna or cable tv signals over Cat6 or Cat7, using an impedance adapter on each end.
Tux2000
No, you don't want to use a voltage divider. A voltage divider works fine as long as the load connected to the voltage divider has a much higher resistance than the voltage divider resistors. If you want to drain 5V @ 2A from a voltage divider, you effectively connect a 2.5 Ohm resistor in parallel to your voltage divider. This may still work (with a really hot milli-Ohm voltage divider) as long as you need constantly 2A. But computers are not constant current sinks, they have a varying need for current. If you know Ohm's law, you can easily calculate that the voltage will not be constant in that case.
Go for a voltage regulator, preferably a switched one with offers a better efficiency factor than a linear voltage regulator. These are standard in all norebooks, plus they run from an unregulated(!) DC input of 8V to 20V.
Desktop harddisks use +12V and +5V, the same applies to optical drives and floppies. Laptop harddisks, optical drives and floppies use +5V only, some newer ones use +3.3V. No component in a PC of the last few years uses -5V or -12V, except the RS232 ports that use -12V for signalising. The new standard for ATX power connectors even change the only pin supplying -5V to "reserved" (i.e. unused). There are many chips for RS232 that generate the required positive and negative voltages (with a low current) from a single +5V (MAX232) or even +3.3V (MAX233) line, so even -12V will soon be obsolete.
You don't need diodes if you use a connector that can't be reversed. You don't need a capacitor if that connector has a lockable connection (like XLR). Remember that a diode between the external power supply and the internal voltage regulator drops about 0.6V (0.2V for a schottky diode), and the entire current for the system (up to 4A in current laptops) flows through this diode. So it is heated with 0.6V * 4A = 2.4 W that need to be cooled or it will die. It is possible to design a DC switched power supply that can stand reversed polarity, because it simply does not start with reversed polarity, so there is really no need for a diode.
Tux2000
Try to buy a professional printer. Not those with a big bright "professional" label, tools with such labels aren't "professional". Look at the vendor web pages what printers they offer for business ("enterprise") use. They may be ugly, big and expensive, but they offer better quality and longer a lifespan than those toys sold for SOHO use.
Search for a printer with Postscript support. It makes life easy with any OS (*BSD, Linux, MacOS, MacOS X, and even DOS and Windows can print on Postscript printers), and at the same time you can be sure that the printer has a real CPU and not just a chip that does nothing more interfacing the printer's hardware to a Windows-only "GDI" driver. Make sure the printer has some RAM, 8 MBytes is the absolute minimum, better try to get 32 MBytes.
The printer should have a build-in (ethernet) print server, or at least an external print server from the same manufacturer. I've seen HP printers refusing to do more than the absolute minimum work (unidirectional printing without any status reporting) until they have been connected to an HP print server. The reason for the print server: Ethernet does not die, it justs becomes faster. Parallel ports become more and more rare these days, many laptops already omit them. USB will some day be as obsolete as ISA is today. USB limits you to 2m printer cable, a parallel port may work with up to 5m, but ethernet gives you 100m. Plus you can share the printer with as many computers as you like, without the need to power up a dedicated computer for printing. And as a nice extra: With a WLAN access point or WLAN router, you can even print wireless.
My Hardware: HP Laserjet 1200N, a LJ1200 with 16 MB RAM plus an external ethernet to USB print server in the box. Yes, it's a SOHO toy (with Postscript support), and I would prefer a LJ 4000/4050/4100, but I got it for free. I've printed 1500 pages without any problems, from Windows, Linux and MacOS 9.
Tux2000
... but make sure you don't run VNC on an unsecured machine connected to the internet. At least close all other ports and tunnel VNC over ssh (see google for how this is done). You don't want a bunch of script kiddies to take over the PC, do you?
Tux2000
Some ATMs are designed for outdoor usage, the "worst case" ATM I saw was simply mounted into a wall with absolutly no wheather shielding. It had to stand rain, snow, storm, and hail. Other Public Terminals are comparable. Both have to withstand really dirty fingers, cola, coffee, often also wheather, and of course vandalism.
On the inside, you often find an ancient major-brand PC, and in case of the ATM, some special hardware to dispose money. Exchanging or upgrading the PC or running some kind of terminal software on it (TightVNC, Terminal Services Client, X11 Server, ...) should be no real problem, the special hardware can be removed, and you end up with a heavy duty PC box with at least a build-in, shielded screen. With a public internet terminal, you also have a "bullet-proof" keyboard and a mouse replacement. Otherwise, add a sealed ("waterproof") keyboard and a cheap optical mouse. Try to replace the tiny PS/2 style connectors with some better, heavy duty connectors (4 pin XLR is the best, DIN-5 or DSUB9 should also do the job), using two adapter cables inside the box and new connectors on keyboard and mouse.
For the software side, try not to store anything on that box, but place all your documents on a fileserver in a more friendly environment. Small NAS boxes are available for around 200 US$. Have a replacement harddisk and an up-to-date image of the system available. Even better, avoid the entire harddisk and boot from the network (search terms: PXE, EtherBoot) or a small compact flash card with an IDE adapter.
Tux2000
Do you remember the story of NASA searching i8086 CPUs for their space shuttles just two years ago? There are other stories, I remember some companies paying a lot of money for ancient Toshiba 386 laptops that was the only computer certified to "remote control" a certian pacemaker. A re-certification of a new system would have cost much more than buying a few 386 laptops at pentium-class prices.
Some systems (not only NASA shuttles) are designed around a randomly selected CPU, and they run with software that needs the exact behaviour and timing of that special CPU. Say hello to the world of embedded systems.
This message from intel is just a warning for designers of embedded systems that there will be a day when there is no spare P-II left.
Tux2000
I don't know what's wrong with dnsmasq+exim (and I'm too lazy to search google), but dnsmasq is under very active development and has fixed a lot of bugs, some esotheric, some really nasty. Details are in the changelog. Perhaps the trouble with exim has already been solved. You may want to give dnsmasq a second chance. ;-)
I still use sendmail from Slackware 8 in my LAN, it just works, with both my now disabled bind and with dnsmasq 2.something. I want to change to some other mailer, but I've not yet found the time to learn and install exim or postfix.
Tux2000
For small networks, I recommend using dnsmasq. It's a combined DHCP server and DNS server/proxy intended for use on a masquerading gateway that can run nearly without any configuration. Add your mac addresses to /etc/ethers for fixed IP adresses, add your hostnames to /etc/hosts, finito. There is no need to fiddle with to big servers (bind and ISC dhcpd). I use it on my (heavily modified) WRT54G with about 10 to 20 systems without any problems.
Tux2000
Hmm, if someone want to protect his data in his network(s), he surely does not want a WAP in that network. Or if he wants a WAP, he has not yet been properly educated. (Well, there may be some reason to run a VPN over WLAN, but you do not want unprotected WLAN.)
Tux2000
I develop and code a web-based database application, that is installed on a dedicated server at our client's sites. In most cases, we also install some kind of remote access software for maintainance. We access this software via Modem or ISDN with or without callback, VPN or special firewall configurations via internet. Some clients even expose the server to the internet.
Our big advantage is that we need only one TCP port (80 for http or 443 for https) with one protocol (HTTP), this is rarely a problem for any kind of firewall or network admin. For remote access, we can use different software with different requirements, depending on the wishes of the clients. SMTP, POP3 and IMAP4 can be handled very similar. Other server applications can be much harder, even such "simple" things like a Windows fileserver needs various TCP and UDP ports, and firewalling such applications can be a major PITA. Even FTP needs at least two ports and contains IP addresses inside the data packages, but either passive mode or a smart firewall can help firewalling FTP.
So, if you "just" need some software based on well-known internet standard protocols, a dedicated server behind a firewall should do the trick. If the vendor wants remote access, add a protected (i.e. callback + token) modem or ISDN line. If you need propritary software, maybe even in a non-IP environment, the things become harder. You may even need to build your own firewall or proxy, perhaps based on Linux or *BSD.
Tux2000
My tips from my experiences - or: how I prefer to work.
Bright Workspace: How: At home, I light my workspace with a 40W fluorescent ring lamp (made by Philips, type "TLE 40W/25") with a cold light color. Its advantage is that it illuminates the entire room very homogenous. The disadvantage is that food looks ugly, especially meat. I work on a white desk.At work, I have to live with two bands of linear flourescent lamps (22W each, I guess) each, shared for four tables. They produce enough light, but it is not as homogenous as the ring lamp. The desk at work has a light wood decor. Not optimal, but it works, because it is usually burried under heaps of paper.
Why: The low contrast between monitor and work environment reduces stress for the eyes. Try it: find a dark room and look onto a bright PC display (TFT or CRT) for a few minutes. I can't stand it longer than a few minutes. Proper Monitor: I prefer high quality CRTs. I own and use several Eizo Flexscans, 17 and 21 inches, and I recently ordered a new 17 inch Eizo Flexscan for my work place, even if (or perhaps because) the company policy is to buy low-cost TFTs. Sure, CRTs are large and ugly, and they need a lot of energy. But IMHO, the image on a good CRT is smoother than on a TFT. There is no color problem when you look from the side onto the CRT. CRTs don't have to interpolate the image to display different resolutions. Proper Resolution and Refresh Rate: For TFTs, look into the manual, but usually, you have to use 60 Hz refresh rate for best quality. And you have to use the native resolution of the display (see manual), or else it will interpolate the image or does not use the entire screen.
For CRTs, adjust the refresh rate to something between 85 Hz and 120 Hz. Depending on the light, there may be some flicker effects if the frequency of your light's power supply and the refresh rate are small integer multiples of a common base frequency: 50 Hz power supply for the light and 75 Hz refresh rate (2 : 3) cause massive flicker on my monitors, followed by a headache after a few minutes. Setting the refresh rate to 85 Hz removes this effect. Use the resolution recommended by the manufacturer of the monitor, or the next smaller resolution. Do not use the theoretical maximum resolution from the data sheet or the catalogue, this is the resolution that just does not kill the monitor, but it is not the optimum resolution.
I recommend to use not more than 1024 x 768 on a 17 inch CRT / 15 inch TFT. Buy a larger monitor if you permanently need higher resolutions. Proper Setup
Wrong! Dangerously wrong! Do you want someone to be killed by blindly believing this statement?
A switching PSU is dangerous after unplugging the mains for quite a while. You know that:
The important statement is that it takes a lot of time for the capacitors do discharge. And you don't really want an amateur to fiddle with a switching PSU, without knowing about dangerous parts and without proper equipment (at least an isolating transformer and properly isolated tools). At least I don't want it.
So, please kids, don't try this at home. Don't open any equipment that operates at more than 40 volts or generates more than 40 volts. Don't try to repair that equipment unless you want a Darwin award or you have had a proper training.
Tux2000
My (expensive) USB flash stick died a few weeks ago, after two years of usage. I could still read it, but it refused to be written. Gladly, my vendor gave me a new USB stick for free, but this is definetly not the media I want to store my important files on.
My backup is an external firewire case with a large ATA harddisk, combined with a script that writes all modifications in the main RAID-1 filesystem to the backup harddisk. Tape drives are too expensive, and tapes wear out rapidly. Burning complete backups to DVD-R(W) or CD-R(W) takes way too long, and you need a huge pile of discs to backup just a few ten Gigabytes. The downside is that there is yet another fragile harddisk that may die some day. My hope is that not all harddisks die at the same moment. That's why the backup harddisk is usually disconnected from both power and firewire.
Tux2000
I assume your friend uses an OS that supports using more than one mouse in parallel, i.e. Linux, MacOS X or recent versions of Windows (98 or newer, 2000 or newer). I assume that your friend can use at least one foot (or hand) to operate a foot switch.
You need two mice, one for the cursor movement and one for the buttons.
The "buttons" mouse should be a cheap one, preferably with a removeable ball and a long cable. The entire ball mechanics is no longer needed, just the electronics. You need one, two or three simple foot switches (temporary contact, i.e. contact is closed only when the foot switch is pressed down). Connect the two contacts of each foot switch in parallel to each mouse button. If your friend needs only one foot switch, you may hide the electronics of the mouse inside the foot switch. If your friend needs more than one switch, drilling some holes into the mouse case for headphone jacks (one for each foot switch) may be a good idea.
The "cursor" mouse can be nearly any mouse. If your friend can't move the mouse without accidentally clicking some buttons, open the mouse and cut off the little plastic pieces below the mouse buttons that press the switches on the electronics board.
Now your friend can use the "cursor" mouse to move the cursor, and the foot switch(es) to click. Even drag and drop should be possible, he just has leave one foot on the foot switch.
I admit this idea may look strange, but I think it is quite usable. Many secretaries use foot switches to control dictation machines. Think about driving a car. How do you accelerate? How do you stop a car? Planes are even directed with the pilot's feet, at least while they are not flying.
Tux2000
... just pay the repair folks. They (should) know what they do.
The other way: get a repair manual, lots of small tools, and a replacement drive that fits mechanically and electrically into the laptop. Fiddle with some of the tools and your laptop. Result: You have a heap of screws, wires, plastic parts, and strange matter you have never seen before, your laptop is now really broken, the new harddrive has not survived, and you have spent more money than the repair folks demanded. Add a large ammount of super glue to the heap,sell it as piece of modern art on ebay, buy a new laptop and make sure it is repaired by experts next time.
Tux2000
That help may be a technical device, like a magnifier, a screen reader, a braille printer, a blindman's stick, an extra large book, a tactile map or globe, or some other "gadget". But as some others have already stated, this may lead to isolation. I don't want to say anything bad about this stuff, I'm glad it exists. But there is another way to help:
TEAMWORK, especially of the students.
It means more work for the teacher: He has to develop tasks that can be solved best by a team, not by a lone warrior. He may have to fight with authorities to be allowed to go an unusual way. He may have to fight with students that want their old multiple choice tests back. But it helps the students learning to work as a team of specialists. I'm sure this helps all students more to get through their lives than to know the Capitol of the South American country to the west of Surinam.
I prefer to work as a lone warrior, but I need my team to compensate my deficits (handling clients, getting the newest rumors, handling company politics). I work this way since five years, I really like it, and I produce excellent results. I learned teamwork at university, way too late. During the last five years, there were some short experiences when the whole team worked like a single mind distributed over a few bodies to avert a huge damage, and these moments were the best. Knowing the Capitol of the South American country to the west of Surinam wouldn't have helped a little bit, but knowing how to work as a team did.
By the way: I know my (handicapped) wife from my alternative civilian service in a sheltered workshop, and I know the problems with the integration of handicapped people. It is a permanent fight and requires a lot of energy from all people involved, especially the parents.
Tux2000
(Mod parent up!)
I once used an ancient Apple Laserwriter 12/600. It produced a feelable amount of toner on the print-outs (I guess 0.25 to 0.5 mm), much more than any other laser printer I've seen. I don't know if it was adjusted improperly or if it was using the wrong toner, or if it just behaves this way. I'm not blind, and I'm not trained to read braille, but I'm sure that a map printed on that old printer would have been feelable.
I think that a solid ink printer could do the same job, perhaps even better. A printer driver for the Apple Laserwriter 12/600 is available at least in Win2000, Win98, Linux and Mac OS, as it is just a plain postscript printer. I don't know how about solid ink printer drivers.
Tux2000