Electrical knowledge, was Another ~1960 computer kit - test-drb@ccmp.vtda.org

19 Dec 1998

I guess this post will also show how weird I am.
At 09:31 PM 12/19/98 +0000, Tony wrote:
...
   But worse still is the fact that back in the early
years of this century, 
it appears that boys - say about 12-15 years old - were expected to try 
woodwork, metalwork, using a lathe, wiring electric lights, bells, 
telephones, etc, making induction coils, etc, etc, etc. Things that I bet 
few boys ever try today. And yet, today, it could be made a little easier 
for them.
  I have some of these books, and it always amazes me what "boys" were
doing 
Some of them are available as reprints from Lindsay Publications (in the 
UK, available from Camden Miniature Steam Services).

Lindsay is at www.lindsaybks.com. I have many too. Have tried to talk him
into having more computer books besides the "How to repair and upgrade your
PC" type.
The "Practical Electronics" TTL calculator would be good if he could do
something like that.

...
   aluminum
casting. Alfred Morgan was writing books like this at least until 
I've never tried it, but I believe that getting a _good_ casting from 
aluminium is not that easy. Sure it's an easy metal to melt, but it also 
picks up all sorts of garbage very easily, leading to a terrible casting. 
Iron/steel is supposed to be easier to cast - if you can melt it. 
I've read the next step up from aluminum, copper or brass, can have its own
problems too.
...

 OFF topic:
 Max wrote:
 There's little need to make coils these days, and wiring electric lights
 isn't very fun when one can play around with things millions of times more
 complex.

 Hey! I've wound several experimental coils this year. Did you wonder _how_ a 
This year? This week, more like :-). 

  transformer works? I know the equations to design
one, but am asking 
It may just be me, but I never like using equations to _explain_ 
anything. Sure they're useful tools when you come to design a transformer 
(or whatever), but you should be able to understand the operation of the 
transformer using qualitative arguements. 
Well, more often than "this year", actually. I like practice and
experiments, but sometime require some equations/theory. Think of a
transformer secondary wound with coax cable. What would happen...
...

> As for wiring lights, Christmas tree light strings here are now cheap series
> strings although the bulbs may have some wire turns wrapped around the leads
> to prevent a open circuit if a bulb burns out. This often don't work, so the
> entire string is usually thrown away, like many modern ASIC type computer
boards
...

You mean people don't get little packets of replacement bulbs and play 
'hunt the dud' any more. That used to be a ritual each winter here for 
many years. 
Apparently not much anymore. Don't have a "Voltstick" type of detector yet.
Are they only AC, or can they pick up the charge on a CRT screen?
...

Those little electrostic field detectors (aka 'Voltstick') took all the 
fun out of it ;-).
 And,

...
 These people didn't have a clue that you could make
logic circuits using 
relay contacts.

Don't get me wrong. I'm totally in favour of digital _electronics_, 
microcontrollers, FPGAs, etc when they're the right solution. But when I 
want to make an XOR gate to control the light over the stairs here, you 
can be sure I'm going to use a couple of changeover switches and nothing 
more. And Max wrote:
...

OK, now I have the feeling I may have forgotten something. When you wire
some bulbs in series, and one burns out, they all fail. If they are wired
in ||, and one burns out, the others keep burning. What more is there? 
True, series and parallel are basic, but not too interesting if you only
stop there! 2 single-pole double throw (changeover) switches can be wired so
either one can turn a light on or off. Like one switch at the top and one at
the bottom of stairs.
Suppose you need a third switch? A double-pole, double-throw one will work.
When you see how it is wired, you see how any number can be wired. And the
light is now a "parity" indicator! (No when I knew how to wire the switches,
had never heard of the word parity yet.)

Another example, it surprises me how many "electrical" people do not
understand, for example, what happens when one wires speakers in series or
parallel.

...
 I wonder how many people here have made a light bulb,
or a cell/battery 
from scratch. OK, on this list, quite a few I would guess. Elsewhere, 
close to 0? What about winding a motor (and that's almost on-topic - one 
day you're going to have to rebuild an LA36, and carriage motors are 
neither common nor cheap...) Yes to all 3.

...
 You can learn a lot more by actually making something
(however poorly it 
actually performs) than by reading a book or playing with a simulation. 
The latter are useful as well (particularly the books), but in the end 
you actually have to try making something.

I heard that a number of physics graduates from, I think US, but it 
might have been UK, universities were given a battery, some wire, and a 
bulb of the same voltage as the battery. The task was to light the bulb. 
An amazing percentage (something like 80%) couldn't do it (and no, there 
were no tricks). 
Sad if true. Thanks for bringing back the memory of a very early experiment
I did. I took apart a flashlight and had the bulb and a D size cell. Both
the bulb and the cell looked like they had one terminal- the metal bump on
the bottom of the bulb and the center metal contact on the top of the D
cell. But when the 2 were connected, the bulb didn't light. So I had to go
back and examine the flashlight more closely, then find some wire. Learning
that way sticks.
-Dave