Kind: captions
Language: en
the modern era of electronics began with
the light bulb
but not in the way you might think
early light bulbs consisted of a carbon
filament sealed inside a glass bulb with
a vacuum inside when a potential
difference was applied across the
filament current flowed through it
heating it up to over 2000 Kelvin so hot
that it glowed if there had been much
oxygen in the bulb the filament would
have burned immediately that was the
reason for the vacuum but from the
perspective of electronics the real
breakthrough came from a curious
observation made by Thomas Edison
he saw that over a bulb's lifetime the
glass became discolored turning yellow
and then brown but only on one side
so what was going on
well the heated filament emits not only
light and heat but also electrons you
can think of them being boiled off the
surface of that carbon this phenomenon
known as thermionic emission had twice
been discovered independently by other
scientists up to 27 years earlier but
after Edison it became widely known in
fact for a Time the emission of
electrons off a hot filament was called
the Edison effect now these electrons
floating around were unobstructed
because they're in a vacuum but since
there was a potential difference across
the wires that led to the filament the
electrons were attracted to the positive
wire so they accelerated towards it and
most would whiz straight past it and
crash into the glass over time
discoloring it only on the positive side
I should note that Edison was using DC
electricity if he had been using AC then
both sides would have been discolored
but it this observation that set the
scene for an Electronics Revolution and
eventually the first digital computers
in 1904 John Ambrose Fleming patented a
device that was very similar to Edison's
light bulb but with one important
addition a second electrode in the bulb
by charging this plate positively with
respect to the filament electrons could
be accelerated across the Gap completing
the circuit but if the plate were
slightly negative relative to the
filament then it would repel electrons
and no current would flow Fleming called
his device a one-way Street for
electricity since only one of the
electrodes was heated electrons could
only flow from there to the plate and
not the other way around the device was
called a thermionic diode and it was
used initially for detecting radio
signals but it could also convert
alternating current to direct current
scientists quickly realized that a more
efficient design had the filament in the
center and the other electrode the plate
or anode as a cylinder surrounding it
this geometry captured more of the
electrons coming off the filament and
allowed for larger currents to flow
oh There She Goes
with just one of these diodes you could
convert AC into a bumpy kind of DC but
combining a few diodes and a capacitor
led to a fairly steady direct current
and this was a big deal it was the first
practical vacuum tube device and the
model for all vacuum tubes that would
dominate the industry for the next half
century
in the early 1900s the big problem in
electronics was amplification radio had
just been invented but its range was
limited by the lack of reliable
equipment that could boost weak signals
similarly telephone calls were limited
to at most thirteen hundred kilometers
because by that point the signal was too
faint to hear
a rudimentary form of amplification had
been built for telegraph operation
called the relay in a relay there is an
electromagnet and when current flows
through that electromagnet it attracts a
switch turning on a second circuit but
when the current through the
electromagnet stops the switch is
released and the second circuit is open
again this device works well for
amplifying the dots and dashes of Morse
code along a telegraph line but its
binary output means it's incapable of
amplifying the complex and analog
signals of phone calls and radio waves
foreign
that's why it was such a breakthrough in
1906 when Lee De Forest took the diode
and added another electrode into the
bulb this electrode wasn't a solid piece
of metal but rather a sparse wire mesh
and it was positioned in between the
filament or cathode and the anode with
three electrodes it was called a triode
now a large potential difference could
be applied across the anode and cathode
but the number of electrons that
actually flowed between them was
controlled by the voltage on the grid as
this new electrode was known if the grid
were slightly negatively charged it
repelled electrons from the filament so
that none could flow through to the
anode but if the grid were slightly
positive then electrons were attracted
away from the filament and most of them
would pass through the holes in the grid
and then accelerate to the anode so in
this way a small change in voltage on
the grid can control a huge voltage at
the anode and the response is so you can
get high frequency amplification I like
to think of it as standing at the top of
a high cliff opening and closing a valve
on a big water pipe I mean it doesn't
take much energy to turn the valve but
that small input is converted into a
huge output of water falling down the
cliff
powering up this Trail I hope you can
see it warming up there
so the yellow is the input and the
yellow is the input purple's the output
we have essentially a two volt change on
the input giving us what is this 5 volts
so 5 10 15 volt change on the output for
this demonstration we were only using 24
volts on the anode if we had used a
higher voltage we could have got a lot
more amplification and people did this
was the device that allowed us to call
long distance for the first time using
vacuum tubes the first transcontinental
call from New York to San Francisco took
place on the 25th of January 1915.
whoa yeah there we go should be 10 volts
it's hard to see the grid here because
just like with the cylindrical diode the
best configuration for a triode is to
have a cylindrical configuration the
anode is on the outside the grid is
cylindrically inside that and the
cathode or filament is in the center
the invention of the triode was
incredibly important radios TVs whatever
Electronics people had were powered by
vacuum tubes you would have had so many
in your house even up until the 1960s
and 70s
but vacuum tubes weren't done
revolutionizing Electronics
in his 1937 thesis Claude Shannon found
a connection between electric circuits
and a branch of mathematics known as
Boolean algebra working in the mid-1800s
George bull was trying to find a
mathematical foundation for logic under
his system a true statement was
represented as a one and a false
statement as a zero and Bool also
developed a few operations like and if
both statements A and B were true then
the output would also be true
what Shannon realized is that Bull's
operations could be represented as
electronic circuits that there was an
equivalence between mathematical
statements and electric circuits all you
needed to realize these circuits in the
real world were a couple switches
that same year 1937 George stibbetts
built the first digital calculator it
could add two one bit binary numbers
that is it could add two numbers so long
as they were either zero or one the
calculator worked using a relay that
electromechanical switch from telegraphy
there were two inputs if they were left
open the input was Zero if closed it was
a one the output was shown with two
light bulbs if no lights were on the
answer was Zero if the output light was
on the answer was one and if the carry
light was on the answer was a 2. and
this circuit diagram works like this if
neither switch A or B is closed so
adding 0 plus 0 then no current flows
through the circuit and no light bulb
would light up but if input a was closed
the current would flow through the
solenoid creating a magnetic field that
pulls the switch inside it closed and
this connects the output light bulb to
power and disconnects the carry light
bulb so the output light bulb lights up
meaning that the answer is one and the
same thing would happen when input B was
closed and a was open
but if you closed both A and B
simultaneously then there is no current
flowing through the solenoid but there
would be a current flowing from the
battery connected to a which is
connected to the carry light bulb so it
lights up indicating one plus one equals
two
this is the beginning of the digital age
and no it was not glamorous stibbetts
built his device out of a few batteries
light bulbs and relays he had lying
around and for the inputs he cut up a
tin of tobacco he built it in one night
at his kitchen table which is why it
became known as the model K the circuit
that stibbetts built is now called a
half adder but if you look at the
circuit Through The Eyes of Claude
Shannon you realize it's actually a pair
of logic gates the output light bulb
should turn on when either A or B but
not both are closed so this is known as
an exclusive or gate whereas the carry
light bulb should only turn on when both
A and B are closed so this is an and
gate this circuit uses electrical
versions of Boolean operators xor and
and it's possible to build other Boolean
operators as electronic gates for things
like ore nor and nand
and you might say what's the big deal I
mean the big deal is that you just
tricked a bunch of electrons into doing
math for you sure it's very simple math
but you could connect a bunch of these
half adders together and build more and
more complicated circuits that could do
more complex math which is exactly what
stibbetts and his colleagues at Bell
Labs did two years later they built the
model one which had more than 400 relays
and could add two eight digit numbers
together in a tenth of a second we could
also Multiply eight digit numbers and do
multiplication of complex numbers though
these more complicated operations took
longer about a minute per calculation
so you put a voltage through a coil and
it'll turn that switch on or off so
you've got your two operands here
and if you want to add two numbers
together so two is this three is this
right so one zero is two
yeah and one one is three and so then
when you want to calculate it you just
hit the go button down here
I love the sound of that that is amazing
it's magical so if you want to do like
say uh uh eight plus oh that would be
four so eight plus eight I think right
okay yeah eight plus eighty six no it
clears it on its own okay
there you go
eight plus eight is uh 16 in binary
which would be one zero zero zero zero
this is essentially a one bit arithmetic
unit there's no logic functions it only
ever does add now let's say we want to
do five minus two the answer is going to
be three so we flip this little switch
here that lets me know that I'm doing a
subtraction operation and we do
subtraction by doing two's complement so
essentially what we're doing is we're
inverting one of the operands and we're
adding one so now when I run it
we can see five minus two is equal to
three so two and one is three now
because of the way that we do this the
final carry flag ends up getting
illuminated here on the end but if we
know that we're doing a subtraction
operation we know that this final carry
flag is never going to be on otherwise
over the next 10 years they built six
more computers based on relays which
were used by the US Military and the
national advisory committee for
astronautics or NACA which later would
become NASA but even by the early 1940s
it was clear that the mechanical nature
of the relay the physical closing and
opening of the switches was too slow to
be the future of computers they were
also prone to Breaking anytime you have
something that's mechanical it's gonna
wear down every time that relay switches
there's a little bit of friction on the
rotation Point inside of there and
there's contacts that are making and
breaking electrical connections and
those are going to wear out and all the
relays opening and closing meant that
the computers were incredibly loud
[Music]
so it doesn't really work in a business
environment all that well you can't
really stuff it into your office that
you're going to drive people insane
[Music]
so what computer scientists really
needed was an electronic switch and that
is where the vacuum tube triode comes in
whoa
I mean sure it can work as an amplifier
if you put slightly positive or negative
voltages on the grid but it can also
work as a switch if the grid voltage is
very negative then no current flows and
if the grid voltage is very positive
then maximum current flows so a triode
can be controlled using no moving Parts
just a voltage will set it to be either
a zero or a one and best of all
switching between the two can be done
rapidly with no noise since you're just
controlling electrons zipping around in
a vacuum this is the invention that took
Computing to the next level
the world's first electronic
programmable computer was called eniac
and it came online for the first time on
December 10th 1945. it took up a whole
room weighed 30 tons and used 175
kilowatts of power so much that it led
to a rumor that every time it turned on
the lights in Philadelphia where eniac
was located would dim
now that was just a rumor but mainly
because eniac had its own dedicated
electrical generator to keep up with the
enormous powered raw unlike previous
computers eniac wasn't limited to just
solving one type of mathematical problem
it could be programmed and it was fast
completing 500 operations per second
at the time the word computers still
referred to people doing calculations
with pen and paper so 500 operations per
second was really fast
eniac's flexibility and power was
immediately useful for the development
of the hydrogen bomb the computations
needed were so complex that the director
of Los Alamos at the time said that it
would have been impossible to arrive at
any solution without the aid of eniac
this is a hilarious part about having a
processor that is one meter tall and 70
centimeters wide is that you can point
at actual parts of the processor this is
what a one bit vacuum tube computer
looks like
[Music]
can you feel the heat coming off of it
I certainly can I can feel the heat
coming off it's getting warm well I mean
190 vacuum tubes is a lot I think we
figured it out this is pulling like 350
or 400 watts of power or something like
that
which is absurd at night it's awesome it
looks like a city
but there were also major flaws with
vacuum tubes the filaments always needed
to be heated so they used a lot of power
even when idle and they were big it was
hard to make a glass vacuum tube with
complex electrodes inside arbitrarily
small they were also unreliable on
average a vacuum tube in eniac broke
down every few days and then it needed
to be found and replaced the longest
that eniac operated for without failure
was just 116 hours
the first digital computers ran on
glorified light bulbs that is why they
were so big Power hungry and unreliable
the miracle and what has made our modern
lives possible is that someone figured
out how to perform the same trick with
electrons inside a solid piece of
material in Silicon but that's a story
for another day
[Music]
foreign
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