Early LCD Projector? – Scanning Method Brings Television Movies (Feb, 1933)

The explanation given sounds roughly like how an LCD works. What do you think the mystery material was that went transparent when current was applied?

Scanning Method Brings Television Movies

THE progress of television has long been retarded by the lack of an efficient light source which could react instantaneously to the fluctuations of incoming radio currents and at the same time be powerful enough to project the image upon a large theatre screen.

This difficulty, however, has now been overcome by the development of a new scanning method which promises to equal or excel the movies as a source of home and public entertainment. This new method dispenses with the neon tube altogether and utilizes as a source of illumination the arc light of the conventional projector.

New “Control Plate” Is the Secret The heart of the new system is a “picture frame,” or “lantern slide,” a small glass plate on which the actual moving scene being broadcast is created. This plate is covered on one side with a fine wire mesh impregnated with an electro-sensitive substance which renders the glass, normally opaque, transparent when an electric current is passed through it.

A scanning disc is used to provide the electrical disturbance necessary to render the plate transparent. This disc, shown in the artist’s drawing above, is made of clear glass with 60 fine wires radiating out from the center like spokes from a wheel, each wire terminating in a tiny brush. These brushes are arranged in a spiral curve, similar to the holes in the metal scanning disc of the conventional television system.

Each brush is spaced from the next by a distance equal to the width of the chemically-coated glass plate. Then while the disc makes a single revolution, the sixty terminals sweep the plate one after the other, with 60 slightly curved parallel lines, each a short distance apart, until the plate is covered from top to bottom. The speed of the scanning disc is synchronized with the transmitter at the broadcasting station.

The chemical coating on the plate, under the influence of the electric current from the passing wire terminal of the disc, becomes transparent in a varying amount, according to the intensity of the incoming radio signals. With these 60 brushes sweeping the plate 15 times a second, the speed of the disc, a moving picture corresponding the scene at the transmitter is built up.

The light passed through the changing transparency of the control plate is projected upon the theatre screen just like any moving picture.

  1. Mike Brown says: March 23, 201010:03 am

    It is a very early ancestor of the LCD.

    According to Jenkins’ patent 1,544,156, the “mystery material” is carbon bisuphide:

    “5 represents a source of light, 9 a lens for making parallel certain rays from that source, 10 a Nicol prism polarizer, 11 an analyzer, 12 an electric coil surrounding a space 13 in which may be a cell filled with bisulphide of carbon. This apparatus between the light 8 and the ring disks 2, 3 is selected to illustrate any possible devices whereby a fluctuating electric current may cause the amount of light passing to vary correspondingly, or control automatically the intensity of light passing from the source to the screen. In the use of the members 10, 11 they are so set as to cut off all light, normally, but in passing through the magnetic field of the coil 12 the plane of polarization of the rays from 10 is rotated proportionally to the strength of the current. If this current be the fluctuating current from the transmission set (as I make it), the light passing from the source 8 to the screen 5′ will be varied, accordingly, between full transmission and entire extinction. The presence of bisulphide of carbon seems to facilitate the rotation of the plane of polarization.”

  2. M.S.W. says: March 23, 201010:25 am

    It would be interesting to see the real picture quality that was projected from this thing. 15 fps scan rate and 60 lines of resolution might be OK viewing on a small “picture frame” screen, but at theater size the imperfections would stand out vastly. Those tiny brush contacts must wear down quite quickly.

  3. Firebrand38 says: March 23, 201010:43 am

    Mike Brown: 1544156

    I believe that it’s 8 that is the source of light.

  4. jayessell says: March 23, 20101:32 pm

    60 line mechanical television!

    Eventualy people will scoff at our 1080p.

  5. Charlie says: March 23, 20101:49 pm

    jayessell: Probably the ones who are buying $5,000 3D Tv’s right now. I really don’t see the point.

    Then again, people said the same thing about color and sound.

  6. Mike Brown says: March 24, 20107:51 am

    > I believe that it’s 8 that is the source of light.

    I believe you’re right. The OCR on Google Patents is often “iffy”.

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