Motion After the simultaneous transmission of pictures and sound had been achieved, the

7.3.4 Motion After the simultaneous transmission of pictures and sound had been achieved, the

challenge of the transmission of motion required a solution to the problem of synchronization, so that when a person opened the mouth, speech would come out at the same time. This is similar to the challenge of the “talkies” in motion pictures.

The basis of recording and transmitting a picture is scanning one line after another from the top to the bottom of a page, comparable to a farm tractor plow- ing a field. The scanning converts the picture into many horizontal lines of vari- able shades, which are then transmitted consecutively. The facsimile machine of the late 1880s was the precursor to television, which sent only a single picture. Paul Niepkow of Germany invented a mechanical television, with a mechanical system of scanning by perforating a spiral of holes in a spinning disk, then the light that goes through the holes hits a selenium sensor that is sensitive to light. The mechanical televisions never became popular, and were totally replaced by the electronic television, which became practical with the invention of the vac- uum tubes.

Philo Farnsworth (1906–1971) made the first working television, which he publicly demonstrated to news media on September 1, 1928. He was born to a Mormon family in Utah, and later moved to Idaho. Farnsworth developed an early interest in electronics, and excelled in chemistry and physics at high school. He discovered that he could use a cathode ray tube (CRT) to generate an electrical television signal without a spinning mechanical device. The CRT is a vacuum tube where a beam of electrons from a hot cathode (negatively charged) is accelerated by voltage from an anode (positively charged) toward a screen equipped with a fluores- cent coating that emits light when struck by an electron. The CRT also has a set of

259 electric fields to deflect the electron beam from left to right so as to scan a single

7.4 INFORMATION TOOLS

horizontal line, and then to move down a small distance to scan the second line, and so forth. He needed a system to convert an image into a beam of electrons, so he used an “image dissector,” which focuses a photographic image onto a layer of cesium oxide that emits electrons proportional to the intensity of the light. The image dissector is not very efficient, because the bulk of the electrons produced are discarded, so a very bright light is needed.

In 1930 Vladimir Zworykin was recruited by David Sarnoff of RCA, and visited Farnsworth’s laboratory when he copied the dissector. David Sarnoff tried to recruit Farnsworth as well, who declined the offer and joined Philco in Philadelphia instead. Vladimir Zworykin invented the “iconoscope,” which is superior to the “image dissector” as it has photosensitive material to capture all the electrons. The commercial broadcast of electronic television began in 1936 in Germany, the United Kingdom, and the United States. A lawsuit over infringement between Zworykin and Farnsworth was resolved in 1939, when RCA agreed to pay Farnsworth 1 million dollars over 10 years, in addition to license payments to use Farnsworth’s patents. Farnsworth left Philco in 1934, and died in Utah in 1971. The commercial broadcast of color television began in the United States in 1950, and required three guns for the colors red, green, and blue.

The dominance of the CRT gave way to advances in the LCD, or liquid crystal display, which can be much thinner. In this system, millions of LCD ele- ments are arranged in a grid, and each act as a shutter that can be opened or closed to control light coming through, plus a filter to produce red, green, and blue lights. The shutters are made of liquid crystals to create polarized filters, and the alignment of two polarized filters determine whether light comes through or not. The advan- tage of the LCD is in a thinner and lighter display; however it is not very efficient, as most of the light generated in the screen is blocked by the polarized light filters.

A more advanced method is the LED, or light emitting diodes. They are semiconductor diode devices that produce colored light directly without filters, and have the advantage of very low energy consumption and long lifetime.

The closed-circuit television is a point-to-point transmission of sight and sound for only the intended audiences and not for broadcast. It is particularly important for work in the military, crime control, banks, casinos and airports for surveillance, and to monitor factory assembly lines for quality control.