in my last video we explored how analog
television works you can check out the
whole video either through this card or
through the link in the description but
here's a brief overview at its core
analog television is just an amplitude
modulated radio transmission where the
strength of a signal dictates brightness
of a light source with the strong signal
producing a bright light and a weak
signal producing little to no light the
television set uses an electromagnet to
deflect the source of light an electron
beam in a pattern called a raster which
is really just a ton of horizontal line
this has the effect of producing a
glowing series of lines on the face of a
picture tube the electronics of the TV
set line up the incoming signal with the
movement of the beam to create an image
with each part of the image being drawn
brightly or darkly along with the
signals instantaneous strength with
everything in alignment you get an image
by far the most complicated part of
making an image appear on the screen is
making that raster pattern the
electronic components and other crucial
parts such as the picture tube and
deflection yoke are primitive by today's
standards but still pretty complicated
we really just need a way to make a
repeating pattern of lines from a light
source there's got to be a simpler way
to do it
enter mechanical television the earliest
televisions actually got some of their
inspiration from fax machines really and
relying on a couple of important
developments so first it was about the
fax machine facsimile transmission
actually predates the telephone
what with images such as signatures
being commercially reproduced over
telegraph wires as far back as 1865 and
the earliest fast flight device being
invented by Scottish inventor Alexander
Bain in 1846 now I'm simplifying a great
deal here but the theory was that if you
could synchronize the movement of a
scanning device with a drawing device
you could replicate an image if you
scanned a piece of paper line by line
and sent a signal over a wire to match
the darkness of the ink you could
reproduce the image by syncing up a
drawing mechanism with the scanning one
these early fax machines worked but they
were very slow nevertheless they showed
us that you could via election
mechanical means reproduce an image
fast forward to 1884 and 23 year-old
Paul Julius Gottlieb nipped cow the
nitkowski
this is the core of most mechanical
vision systems this cow realized that a
spinning disk could methodically scan an
image line by line simply by placing
evenly spaced holes in a spiral pattern
this is a homemade nipkow disk I took a
really awful vinyl record that I'd be
happy to destroy and marked 32 divisions
around the circumference like 32 very
skinny pie slices then I methodically
drilled a hole along these lines with
each hole being drilled 1/32 of an inch
roughly point 8 millimeters closer to
the center than the left the result is a
spiral pattern of holes this might not
seem like much but it's actually
extremely clever if you put a square
fish shaped mask in front of the holes
its height being slightly less than the
distance between the holes you've made a
device which mechanically creates a
raster scan using these physical holes
John Logie Baird realized that with this
nip Cal disc you could in theory focus
an image with a lens onto the disk and
you could use a light sensor to give an
instantaneous reading of how bright each
part of the image was with the holes in
the nib calvinist certainly has a way to
divide the image the transmittable
pieces back in 1873 Willoughby Smith
discovered the photo conductivity of
selenium and with this knowledge Baird
used some selenium to create the light
sensor for his televisor
I've mounted this NIT Cal disc to an AC
motor which will spin it at 1800 rpm
giving a complete revolution of 30 times
per second before I turn it on look
through the mask I've put an extremely
bright LED behind the disc so you can
see the holes as I slowly turn the disc
you'll see that only one hole is visible
at a time and each hole gets closer to
the left than the next one when I switch
the motor on the holes blend into the
moving line and as it gets faster the
line seems to widen into a square this
square is very uneven because my
homemade nib cal disc was made hastily
and with poor precision but here's the
key only one of the holes is actually
visible through the mask at any given
moment it's just moving too fast to see
Baird used the selenium light sensor to
create a signal from an image being
scanned by the disc and on the receiving
end another identical disc would spin at
precisely the same speed and a light
source such as a neon lamp with various
brightness along with the signal
strength presented by the light sensor
and thus you'd get an image I shall now
attempt to show you how this works
now before you get too excited I will
admit that my mechanical television
doesn't work as well as I had hoped and
that's all on my insistence and using
crap a headline around rather than going
through the process to make a proper led
driver however I hope you'll get an
understanding of what's going on this 10
watt LED chip is what we'll use is a
light source it's really bright and
importantly it can react very quickly to
changes in the voltage it receives first
I'll simply power the LED continuously
as the disc spins up the lines start to
blend into each other and eventually the
whole screen is illuminated now I'm
going to switch the LED on and off at a
higher and higher frequency first five
Hertz the screen appears to just be
flashing nothing too extraordinary but
you might be able to see some odd stuff
happening as the light switches States
now I'll switch it on and off at 60
Hertz something odd starts to be visible
here see if the disc makes a complete
revolution 30 times per second and with
the light flashing at twice that
frequency only some of the holes are lit
up as the disc passes over the LED now
let's move to 1800 Hertz frequencies
that are a multiple of 30 will appear
stable as an even number of pulses fit
within each revolution if you mess with
that though things get weird bubbling
the frequency of just attack makes the
pattern move in relation to the disk the
holes in the disk are directly
responsible for creating the patterns
you see without the disk the led appears
to just be continuously illuminated but
it's not it's flashing really quickly
the disk allows for that flashing to be
visible because it physically obscures
different parts of the light source over
time this is just like the electron
being in the CRT television except
instead of electromagnets moving a beam
across the surface of a picture tube the
light source is physically moved to be
the location of these holes it's a
pretty crafty way of producing a raster
scan and it actually works
this is the best imagery I could get my
televisor to produce this pattern was
generated through manipulating audio
samples in audacity to give you an idea
of how poorly this mechanical PD works
well the image I intended to make was
not a map of the world as this vaguely
suggests but that of a circle here's a
look at true video what you're seeing
here is a very low contrast a very low
resolution image of Seth Meyers I mean
obviously how could you
not recognize him yeah okay it's garbage
but you can see here that there's
certainly something there and it's
moving slightly like a talk show host
Ted Mike when said talk show host is
talking on his show to make this image I
simply place my phone behind the
televisor with the screen brightness all
the way up and I place the solar panel
with an audio cord patched into it into
one of my trusty tascam dr-05 audio
recorders which I use all the time in
fact there's one in my pocket right now
and yes that's directly from a solar
garden light the solar panel would
produce a high current whenever it saw
bright light and it would produce low
current with left like the as the disc
spun it would only allow the tiniest bit
of damage through to the solar panel at
any given time this would produce a
quickly varying signal with amplitude
corresponding to image brightness the
tascam would just encode these relative
brightnesses as sound samples at a
sample rate of 48 kilohertz and then
because I'm really lazy I just hooked my
LED into an audio amplifier and played
that sound back the LED would become
brighter with a stronger signal from the
amplifier though as it's a diode it
would filter out any AC components of
the signal quite honestly I'm amazed it
produces anything at all I opened the
file in audacity just to see what it
looked like and it's pretty intriguing
here's what it sounds like for those
interested
now in case it's not obvious let's go
over the reasons mechanical television
didn't catch on first up until now I
have not let you hear what this sounds
like here's what a 12-inch vinyl disc
sounds like at 1800 rpm
I'm sure that would never diddle but
aside from that there are just so many
practical concerns with mechanical TV
first of all the image is tiny and it's
a horribly low resolution only 32 lines
that's the only reason a signal can be
recorded as an audio file not a lot of
bandwidth is needed because the disc
obscures almost all of the light source
hardly any light gets through this LED
is freakin bright it's painful to look
at directly and yet through the NIT
powders nearly all the light is blocked
and it produces a dull image when these
devices were first in development the
light source would often be a neon lamp
like the orange light in a power strip
switch imagine cause dark damage would
be with only that for a light source
one of the biggest troubles with
mechanical television is image
synchronization because we're using a
big spinning thing to divide the light
of the chunk the disc has to be in
precisely the right place if you want
the image to land where it should if we
take the mask away you can see that the
image just repeats itself over and over
but each of jacent image is actually
shifted one line up or down the most
critical part of synchronization was
ensuring the disk is spinning at the
exact same speed as a scanning disk of a
camera but it would also be necessary to
slow down or speed up the disk in flight
increments to get the image aligned with
the viewing left and with the top and
bottom in the right place but the most
damning problem is that of geometry
imagine we wanted to make a display with
the resolution and size of this small
CRT television well the face of the tube
is about 15 centimetres wide with 480
lines of resolution there would need to
be 480 holes in the NIT count disk
remember only one hole can be seen for
the mask at once for this to work so the
holes would have to be at a minimum 15
centimeters apart so that if
circumference would have to be 72 liters
with the diameter of roughly 23 metres
or 75 feet I live in a building that
stick stories tall a mechanical
television to rival this TV would be
taller than my building and it would
have to spin at 1,800 rpm just like this
one to make 30 frames per second
possible this thing scares me spending
that fast I'm pretty sure it's 75 foot
disk will just explode in fact let's do
the math a 72 metres circumference means
that the edge of the disk would travel
2.16 km/s or well above Mach 6 yeah if
the disc we're rolling it would make it
from New York to Los Angeles in about 35
minutes not in a straight line mind you
but by traveling along actual roads so
the bear television system didn't get
too far
it was certainly genius and is an
important part of the history of
television when it was far too limited
clunky and to be honest had crappy image
quality I've added some links in the
description to videos of mechanical
televisions that actually work and I
think you'll agree that they're pretty
cool but it's a damn good thing they
didn't become mainstream as always thank
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