>> Perhaps you would have enjoyed a visit to Stoney Stratford telephone
>> exchange. It's a sprawling building, filled with rack after rack after
>> rack of cases, each case filled with dozens of relays. And they're not
>> in cases or anything, just "naked", so you can see (and if you desire,
>> move) the working components. There is also several tonnes of wire
>> overhead feeding this equipment. And all of it is as silent as death.
>> It's like a museum or something.
> 
> Some time ago I was reading a Wikipedia entry about some of the relays 
> in a central office. Someone described the sound as deafening back when 
> everything was electromechanical. Especially on heavy phone traffic days.

Looking at this cavernous, echoing building stuffed *litterally* to the 
roof with densly-packed racks of switches... Christ, it must have been 
like hell on Earth! Deafening would be an understatement!!

>> Myself, I visualised a computer made of pressurised water fed through a
>> series of simple mechanical valves. Sadly, I fear that for reliable
>> operation, you would need inside water pressure. And if you wanted a
>> clock speed of more than about 0.02 Hz, you would have to use steel
>> piping and pyrotechnics to sustain the necessary pressure! It would be a
>> very "kinetic" experience though.
> 
> Hmm. Water hammer. I can't imagine it working purely on water pressure 
> alone, though. I keep thinking solenoids to control the valves. Would 
> that be cheating?

Think about how a transistor works: You have one circuit that controls 
another. So how hard would it be to rig up a valve where pressure from 
one pipe moves the valve allowing (or blocking) water from flowing 
through a seperate circuit? In principle it ought to be pretty trivial. 
(Of course, making a valve that actually works well in practise probably 
requires far more equipment than I personally have...)

The problem is going to be that once you have more than a few of these 
linked together, effects like gravity and insertia become significant. 
These don't affect electronics, for some reason...

>> Also... when I tried to build my own machine out of 7400s, I quickly
>> discovered that the gates don't appear to function as their truth table
>> indicates that they should. (!) I also looked into playing with FPGAs,
>> but the cost is prohibitive. (And, knowing me, I'd just make something
>> that doesn't even work, and then spend months trying to find out why!)
>> Plus, Xilinix (?) have a free simulation tool available, and it's just
>> painful to use. I dred to think what actually synthesizing with it would
>> be like...
> 
> They do. If, however you have the gate connected to a switch, and the 
> switch opens the circuit, you'd better have a pull-down resistor, or the 
> gate will float. TTL is rather forgiving of this, the input will float 
> high (e.g. it will be interpreted as a 1) CMOS, on the other hand, can 
> potentially self-destruct if an input is left floating ;)

Maybe that's what I did wrong... I was expecting an open TTL input to 
float low. Anyway, I don't think I shall go down the FPGA route. (!)

>> In solomn truth, it's probably simpler and easier to code a small peice
>> of JavaScript that controls a little Flash animation on a computer
>> screen. But there's something impressive about being able to pick up a
>> physical object in your hands and see that there really are no tricks...
> 
> Yes, but, as you say ... there is something impressive about a physical 
> object. :)

Indeed.

Another thing I thought about was a lego-style kit where you have lumps 
of plastic in the shape of logic gates, with nice connectors for the 
inputs and outputs, and LEDs in each input and output to indicate which 
logic state it's at. The trick, of course, is power routing. ;-)

-- 
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http://www.zazzle.com/MathematicalOrchid*

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>> 5 amps?!
>>
> 
> 5 amps per PCB. If IIRC TTL uses 250 ma per chip and there were 20 chips 
> per PCB and 6 PCBs. Include the losses in the PS and it was just less 
> than a Kw. It glowed <joke>

I've *seen* solid-state equipment glow. It's not funny. o_O

But anyway... 250 mA per chip? I thought it would be more like 0.5 mA 
per chip?

>> How thick was the damned wire??
> 
> Standard for the time. ;-)

Are we talking about the days when wires came insulated with fabric 
rather than plastic? :-P

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Mike Raiford wrote:

> 30 AMPS? O_o

My kettle draws less than that.

(Still, it does operate at a drastically higher voltage...)

>> Does your wife know about this ?
> 
> She does. She's surprisingly tolerant of my antics. ;)

Damn, nice job!

>>> The TTL version should be fun, too. I plan to have lots of LEDs to show
>>> what's happening inside the machine.
>>
>> I hope that you have comprehensive fire insurance :-P
> 
> We do! I think ... I better read my policy closer... I expect the relays 
> will use quite a bit of current, which is why I want to be able to keep 
> the thing as small as possible in the number of relays.

The nice thing about relays is that they're (usually) double-throw. That 
means you need fewer relays than you would, say, transistors.

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>>> Still more complicated than my own 1984 design. ;)
>>
>> Anybody else attempted this crazy task?
> 
> In the mid sixties I built a binary adder using a couple of relays and a 
> uniselector (from the GPO).

Not the GPO!! >_<

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>> What the heck did you search for?! It's kind of a rather specific
>> question...
> 
> I searched for "newton apple myth".  First hit took me to a page that 
> linked to this.

And that WORKED??

>>> You might refute it, a straw poll might be a start, but a poll of 20
>>> people isn't a particularly statistically valid poll.
>> Well it would be more valid than a straw poll of *one* wouldn't it? :-P
> 
> I don't think statistically it would be.  A sample size that's too small 
> is too small.

I don't think stats works like that. You get a number which indicates 
how accurate your estimate is. You them apply some arbitrary threshold 
to decide what is "valid" and "invalid". Choose the right threshold and 
anything can be "valid". My point is that a larger sample size will give 
a better result (assuming reasonable sampling).

> Still, you might give it a go anyways, if anything it'll 
> get you talking to people in meatspace. ;-)

In other news, I just spent an hour and a half in a pub.

>> Still, I guess this is going to be one of those things where no matter
>> how much evidence I produce that nobody has heard of these people,
>> everybody will continue to assert that my statistics are just wrong...
> 
> That's because you don't *have* statistics.  You have a guess.  You say 
> "nobody", but to prove that, you have to prove that *everybody* hasn't 
> heard of them.  That's pretty easy to disprove.

Clearly I meant "nobody" in the sense of "a very small fraction of the 
population" rather than "zero people in the entire world". :-P

>> Quite a few of the names look hard to pronounce, but we'll see...
> 
> Such as?

Sagan?

Rechecking the list, it doesn't look so bad...

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>>> Ah, this would be the perfect time to mention Dijkstra.
>>
>> Oh I am *so* not pronouncing that! :-P
>>
>> I would also suggest that he is famous only to computer experts.
> 
> I am afraid so. Though he could (and possibly should) have been a 
> celebrity for the common man also.

Hey, I never said these people weren't important, I said they're not 
well-known. ;-) Whether this is justified is an entire *other* question...

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andrel wrote:

> I'd say that using a speech synthesizer to sing is a bit cheating.

[insert witty remark here about mass-produced electronically engineered 
pop vocals]

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>>> You would probably find QI interesting, not always about sciencey
>>> stuff, but a good programme to watch.
>> I do sometimes watch that, yes. Although it's not especially easy
>> figuring out when it's actually on TV. But if somebody else discovers
>> that it's on, I'll sometimes sit and watch it.
> 
> http://bbc.co.uk/qi seems to be a pretty definitive source for that 
> information.  But googling "qi schedule" turns up some good hints as 
> well. ;-)

Yes, obviously it hadn't occurred to me that these days the data is 
probably online.

>> I think meeting Mr Fry might possibly be almost as interesting as
>> meeting Einstein. ;-)
> 
> I'm quite sure he'd be more interesting. :-)

I'm not so sure... but neither claim is falsifiable, so...

>> You could live in a dark hole under a rock somewhere and you'd still
>> know who Einstein is. ;-)
> 
> Have you talked to someone who lives in a dark hole under a rock 
> somewhere and asked them? ;-)

Well... not literally, but I've come close. ;-)

> I could argue that you could live in a dark hole under a rock somewhere 
> and still know who Jane Goodall or Richard Dawkins was, too.

Good luck with that. Dawkins I've heard of, Goodall I haven't.

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Mike Raiford wrote:
> Some time ago I was reading a Wikipedia entry about some of the relays 
> in a central office. Someone described the sound as deafening back when 
> everything was electromechanical. Especially on heavy phone traffic days.

I remember talking to someone who worked in a CO when Kennedy was shot. He 
said they thought something was wrong because everything went really quiet 
for about 20 minutes, and then it went completely nuts, beyond the capacity 
of the system to switch.

Altho this might have been with a #5 crossbar. I'm not sure the relays were 
around at the time.

-- 
Darren New, San Diego CA, USA (PST)
    Ada - the programming language trying to avoid
    you literally shooting yourself in the foot.

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>> Do you know what the likes of Einstein command? ;-)
>>
> 
> He was a patent clerk. I'd venture to say at the time he was living his 
> salary was not above 5 digits...

Emphasis *was*. ;-)

>> You've got to admit, though, that mathematics and science are not
>> spectator sports. It can be very interesting to do yourself, but
>> watching the greats of the day doing it isn't particularly interesting.
> 
> True ... but seeing what they discover is very interesting :)

Sure, *after* they've discovered it. ;-)

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