*** BUILD YOUR OWN MECHANICAL TELEVISION SYSTEM ***
By Peter Yanczer
This is the first
of a series of articles developed to guide you in the construction of a pair of
instruments, when connected together will comprise a mechanical television system
able to provide very recognizable images.The
unit to be considered for construction will be the receiver/monitor or display
and to be followed possibly later, a direct view camera. More about this later.
This unit will be equipped with Nipkow disc. The display unit will look something
like the photo the right. The skills necessary to build this mechanical television
system will include working with wood, plastics, metals, optics and electronics.
If you don't have these skills now, this project will give you the opportunity
acquire them. In some cases, "special tools" may be required or when
necessary, you can set up what are known as "work arounds". Depending
on your skill level, you may find it necessary to have someone, possibly a friend
or school instructor to help you out of the "tight spots". This shouldn't
occur very often.
Whenever possible, I recommend that you use your ingenuity
and try to do the task at hand yourself. Get information anywhere you can, but
do the actual work yourself. Don't hesitate to do things over again (and again)
and get them right. This can be an important learning experience for you and the
more you manage to do yourself, the better off you will be.
A point of
interest is that while John Logie Baird of Scotland did most of his work with
a 30 line, vertically scanned system, some of his earlier work was done using
32 lines, the same as the system being considered here.
The display unit
to be described here is based on a physical design by Grant Dixon, a member of
the Narrow Band Television Association, (NBTVA).
Peter Smith designed the electronic circuits for the monitor. Peter is also a
member of the NBTVA. Check out the NBTVA web site. I am a NBTVA member and suggest
you become one too.
This design will be based on successful past work
of a similar nature by the author. Here on the right is a rear view of the receiver/monitor.
technical support where necessary will be limited to NBTV members. Non-members
can request support by Email or the USPO. If you are not
yet a member of the NBTV, I again invite you to join us in this fascinating hobby
now. We would be very pleased to have you with us.
This web site will
include sufficient information to guide you in the construction of this unit.
The plan is to provide additional information on a monthly basis. As you progress
in the construction, I too will be will be constructing a unit for myself. Progress
on my unit will be documented on my web site, enabling you to make comparisons
with your construction.
Since there will be no kit of parts available
for this construction, for some parts, a range of specifications will be called
out for you to consider. For instance, the requirements for the motors to drive
the scanning disks will described in that manner. Other elements of the construction
may simply leave most of the "design" up to you. There will be many
opportunities for to use your ingenuity and give your project that personal touch.
Let's start out by defining what the system will be. This will be a "new"
system for you and for me both.
So the specifications at this point will
be for the most part, just goals. So don't be surprised if changes occur as we
go along. You or I both can change them as needed, to suit our situation at the
moment. This might be because you have a certain part that you want to use or
because we don't have a certain part and want to incorporate something else that
we do have. This might also occur if we lack certain tools or skills, but know
of a way around the problem, if we can change an appropriate specification.
are the specifications we will start with. It is purposely brief so we can add
to or change it as we go along.
Display unit: 12 inch diameter Nipkow
disc. Scanning format: 32 lines, scanned vertically.
Aspect ratio: 2 vertical
to 1 horizontal (2:1)
Scanning starts at the lower right edge of the image,
progresses to the upper left , then repeats.
Image Frame rate: 12.5 hertz
Composite video signal input: 1 volt p-p, with sync pulses most negative, white
Sync level: 0 to 25%
Video level: 25% to 100%
is what we will start with. With this much, we can define the scanning disc, some
of the particulars of the light source and say a few things about the cabinet
or case of the display unit. We can also begin making a list of parts we will
soon need to progress beyond this point.
Materials you will need for
* 12" Aluminum square or circle. Alternate
materials are listed below.
As good a place as any to start, would be
for you to build your scanning disc. You might as well make two at the same time
because the camera, to be built later will need one also. There is a place on
this site that shows a way to build a scanning disc. Refer to that as one way
to do do it. You might also look in some older books or magazines from the early
1930s, or late 1920s for this information.
Now you need to select the
material for the disks. My preference is aluminum, from .015 to .030 inches thick.
And you want it to lay flat. I also have used .060 engraving stock. It works very
well. You can even use cardboard if you like. Many of J. L. Baird's first discs
were cardboard and his larger discs were plywood. One of C. F. Jenkins kits included
a cardboard disc, that wasn't even round. It was eight sided, like a stop sign.
Some experimenters have used semi ridged vinyl or even a 12 inch LP record will
do the job. Take your choice, but if you do use something like cardboard, you
need to be more careful with it as you progress with the building. Also, if you
don't have one, this might be a good time to purchase (or at least borrow) a dial
type vernier caliper . For this project, a 6 inch caliper is adequate. This will
offer you the means to accurately measure dimensions in thousandths of inches,
at a cost of less than 20 dollars. I've seen them at prices as low as 15 dollars.
Properly cared for, it will last you a lifetime.
When you have your material
selected, locate a center point and scribe a 12 inch circle. Cut or saw the disc(s)
out of the sheet of material. At some point you will need some sort of hub for
the center of the discs, to mount them on the drive shaft. If you have nothing
in mind for this yet, for now just put a .375 inch hole in the center position.
Put the disc on a round shaft and spin it to see if the outer edge runs reasonably
true. It ought to be within a 1/32 of an inch. If it is only a little worse than
that, go with it, it will probably do. If it bothers you, you can always make
another one later.
Probably the easiest way to locate the angular position
of the holes is to first scribe the 12 inch circle then divide it in half, and
each half, divide it again. Divide each of the quarters again, giving eighths
and twice more until you have thirty-seconds. The scribe lines are the angular
locations of the thirty two holes.
The first scanning hole in the is located
.250 inches from the disc edge. Pick a line and mark the location of the first
hole. Lightly, center punch it. Measure the distance from the center hole to this
first hole and note its dimension. Reduce this dimension by .015 inches and mark
and lightly center punch the second line (going counter-clockwise) at this new
dimension, measuring again from the center hole. Reduce the dimension by another
.015 and mark the third hole location. Repeat this process for the remaining 29
The holes are drilled with a #72 drill bit, (.025"). Purchase
a few of the drill bits in a "high speed" grade. A hand drill should
do nicely. Better yet if you have or can borrow a drill press. If necessary after
drilling, de-bur the holes. This disc will provide an image size about .52 inches
wide and 1.1 inches high.
Now you can add a row of synchronizing holes,
all on the same radius about 1.50 inch from the edge. Mark and center punch each
of the 32 scribed lines at the same radius and in line with the image holes. Drill
these holes using a .062 drill bit. De-bur if necessary.
Paint both sides
of the disc (unless it's already black in color) using a can of flat black spray
paint. Not to much paint around the scan holes please.
Except for the
hubs, these discs are complete. In the meantime, you might think of ways to mount
your scanning disk to a shaft mounted in bearings of some sort.
would rather buy the scanning disc, I have them available for $85 postpaid in
the USA. These are high quality precisely made laser cut metal discs, with spokes
that improve performance. These discs have a 3/4" center hole.