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May I suggest instead the slightly more modern, voltage tolerant and lower power CMOS 4000 series?

Chances are your hearing loss is limited to a contiguous range of frequencies. Probably a bell-shaped curve. If such is the case, you could probably design (or get an EE acquaintance to design) a low-cost amplifier with a band-pass filter.

I'm thinking a single 2907 quad op amp could handle the mic input amplification, bandpass filter, and output gain. Connect it to an LM386 400mW audio amp chip, and you're in business. While I'm not affiliated with them, I have used futurlec in the past, and they have everything you'd need to build such a circuit yourself. If you want a custom PCB, you can even use the free eagle software to lay it out, and Futurlec can have it printed (in China) for you. Expect about a six-week turnaround.

My old 4x4 keypad phone doesn't have a C key.

Probably because it's only a 3x4 keypad phone. You want a keypad like this, the C is on the same row as the 7, 8 and 9.

You may also want to review your counting skills. ;-)

Technically, the IEC power connector, as found on the back of most computers, is one of the best. You usually see a chassis-mount IEC male connector and a cord-mount female connector, but the reverse forms are available. IEC "wall sockets" are sometimes found in rackmount server outlet strips. The plug is shrouded, and the socket has an enclosing slot for the shroud, so at no time are energized pins exposed. The shroud engages the enclosing slot before the pins make contact. That's a key safety feature. It allows a smaller plug; if exposed pins are energized while the plug is being plugged in, the plug has to be made larger to keep fingers away from the pins.

IEC is a flat-pin design, which is good. Getting a large contact area on round pins is hard, so round-pin connectors of a given size usually carry less current. Flat-pin contacts just slide between two flat spring-loaded blades, which can accommodate wear on both surfaces. The split-cylinder contacts of round-pin female connectors have to match closely, so as they wear, the inside radius of the cylinder increases and no longer properly matches the pin. Round pins vs. flat contact blades are sometimes used; they wear better, but the the contact area is small.

The older round-pin European connectors are only rated for 10A, sometimes only 7.5A. At 240V, this is adequate. IEC connectors are rated for 15A, and there's a 20A form.

Today we expect connectors to just work, but it took considerable engineering to get to that point. As late as 1980, computers had serious problems with connector unreliability.

They use a PIC18F2455. A PIC18 with 24KB of flash and 2KB Ram and USB for about $5.

http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1335&dDocName=en010273

You can use C too, judging from the app notes. Handy for USB stuff.

I'll put it a vote for the Butterfly as well, although you had better get yourself a JTAG programming cable for when you overwrite your bootloader code (as my friend did).

It's easy enough to fix, but you will need a JTAG programmer eventually. You can build your own, but I found that this one worked best for me.

http://www.futurlec.com/ET-AVR_JTAG.shtml

While I appreciate your sentiment, there's no time like today for the electronics hobbyist. Granted, you can't design something on the level of today's PC in your basement on a shoestring budget, but you can build 1970's and 1980's era hardware for song these days. Check out Futurlec for an example. And some places offers PCB fabrication for around $2.50 per square inch.

Times have changed:

• In 1984, an Apple IIe system was around $2500. Nowadays, if you can even find a 6502 processor, they're only a few dollars. You could probably build a complete Apple IIe replica these days for around $100 in parts, including the PCB fabrication.
• In the 70's and 80's, TTL parts were several dollars a piece and consumed 50 to 100 mA per package while offering top speeds of only a few megahertz. Today, the CMOS equivalents cost only tens of pennies per package (at retail, no less), consume only a few microamps of current, and run ten times faster than their TTL ancestors.
• As part of a hobby project, I designed a CPU using only discrete gates, and I estimate it would take about 80 IC packages, including the main memory system. At today's prices, the ALU would cost $12; the instruction decode and control logic ~ $18; and the register pack (sixteen 8 bit registers) $17.
• The capacity of batteries has increased several times - today, I can get 2500 mAh AA rechargeable batteries, where 20 years ago even the D cell NiCds were only 300 mAh.
• Today, thanks to the internet, you can have a fab house build your PCB for you - you can design circuits and have them built without even picking up a soldering iron. Some of these places will build boards for under $100 if you're willing to wait a few weeks.
• In light of the above, today you can build a battery-powered computer system from discrete gates for less than $100. In 1970, you couldn't even run TTL off batteries. And if you did build a system from only TTL gates, it would have cost more than the Commodore 64.
• If you follow the more practical route and use a motorola or intel 8086/8088 processor, you could build the mainboard (cpu & memory) for under $20.
• Atmel, etc... already offer USB controllers with embedded AVR microntrollers. For a few dozen dollars, you too can build your own USB interface board for your project.

So there's no time like the present for the computer tinkerer. Sure, you can't match the performance of today's processors with something you'd put together in your basement, but you don't need to. Even a 100 MHz DSP can encode NTSC video in real time.

What has changed is that the average system of interest to the hobbyist is now 100 or 1000 times cheaper than it was in 1970. In 1970, $50 worth of electronics wasn't even programmable, but today it can run Linux and can hold more code than the average hobbyist could generate in 10 years.

Are you talking about the IP and TCP checksums, or the Ethernet CRC? I just checked the RTL8139B and RTL8139C (you know, the most common Realtek chips out there), and they don't have anything except basic Ethernet framing (including CRC).

On the other hand, Intel's 82559 chips apparently do have it. I have no idea how common those are, though.

I haven't checked the rest.

I asked for datasheets because I've seen a number of people claim to have seen this, throwing around various brand names, without actually being specific enough to allow their claims to be checked.

I suspect that most of today's brand-new on-board Ethernet chips now support TCP, IP, and UDP checksumming, and possibly packet reassembly, but that's a far cry from most Ethernet interfaces that are actually deployed in the field.

On the other hand, obsessive gamers tend to be running next week's hardware anyway.

Help me get a flat scr
here is a new flat scr going for $0.65usd, and they charge $3.00usd for shipping.. it's item C106B1

Note to self, PREVIEW! (Slashdot doesn't seem to do the TT tag the way one would expect!)

I built a 2X2 for switching two computers to either earphones or speakers.

Two DPDT switches, one controls input, one controls output.

(ASCII art deleted because Slashdot can't deal with it.)

1 and 2 are connected together, i and o are inputs and outputs, left and right. Tie all grounds together, switch L+R. I guess doing that could cause a ground loop hum, but it hasn't caused a problem for me. There isn't really a pop or anything when you switch mine, even with the speakers on. You need reasonably good quality switches though, if the switch feels loose or wiggly, it will probably cause a lot of static when you switch it. I found a lot of my surplus switches were not up to audio use. I eventually settled on push-on push-off switches I scavenged from an old set of speakers, they were power and bass boost switches.

This concept is the same way one would build a switch with many more inputs or outputs, you just need rotary switches, DP#T where # is the number of things to switch.

Here are some switches

The 2 pole 5 position and 2 pole 6 position from there is probably what you want. You can cascade a DPDT and two 5 position rotary switches for 10 outputs with one input or vice versa. Scavaging from manual computer switch boxes is probably not a good idea, since most of those are low numbers of positions, with high number of poles.

I built a 2X2 for switching two computers to either earphones or speakers. Two DPDT switches, one controls input, one controls output. i1 i1 i2 i2 1 2 1 2 o1 o1 o2 o2 1 and 2 are connected together, i and o are inputs and outputs, left and right. Tie all grounds together, switch L+R. I guess doing that could cause a ground loop hum, but it hasn't caused a problem for me. There isn't really a pop or anything when you switch mine, even with the speakers on. You need reasonably good quality switches though, if the switch feels loose or wiggly, it will probably cause a lot of static when you switch it. I found a lot of my surplus switches were not up to audio use. I eventually settled on push-on push-off switches I scavenged from an old set of speakers, they were power and bass boost switches. This concept is the same way one would build a switch with many more inputs or outputs, you just need rotary switches, DP#T where # is the number of things to switch. Here are some switches The 2 pole 5 position and 2 pole 6 position from there is probably what you want. You can cascade a DPDT and two 5 position rotary switches for 10 outputs with one input or vice versa. Scavaging from manual computer switch boxes is probably not a good idea, since most of those are low numbers of positions, with high number of poles.