The present invention relates to automatic switching devices and, more particularly, to a programmable non-duplicative switching arrangement for use with a cable television system. The cable television industry has grown rapidly as a result of the demand in many television market areas for an increased selection of television programming. A metropolitan area having two local television stations may also have a cable television system providing additional programming from stations in other metropolitan areas. It is inevitable in such a situation that at various periods during the day a local station and a distant station on the cable will be providing the identical programming. In order to prevent dilution of the advertising effectiveness of the local stations, an FCC regulation provides that the distant station signal must be removed from the cable during those periods. Generally, the local station signal will be switched onto the cable in place of the distant station during duplication periods so that the viewer will not need to change the station setting on his receiver in order to view the program.
It will be appreciated that the switching required to prevent duplication must be rather precisely timed and, therefore, it is generally impractical to rely on manual switching. Several automated switching units have been developed in order to provide the desired switching control automatically.
In one prior art device, the non-duplication switching is controlled by a diode matrix arrangement in which diode pins are plugged into a matrix of pin sockets to indicate the time and day of a desired switching operation. The matrix is sequentially scanned and switching is accomplished in response to detection of the diodes. This diode pin arrangement is somewhat expensive and, additionally, the pin sockets and pins may not provide dependable electrical connectors after extended use. Additionally each of the diode pins is relatively expensive and replacement of broken or lost pins can be a substantial maintenance cost.
Another prior art switching control uses a magnetic disc memory for storing switching information. A significant amount of switching information may be stored with each day of the week broken down into one minute switching increments and up to 13 output channels controlled. This device is relatively expensive, however, and requires a trained operator for programming.
A simpler switching arrangement is shown in U.S. Pat. No. 3,686,573, issued Aug. 22, 1972, to McVoy in which business machine cards are used to control switching. Each row on the card corresponds to a particular switch and each column represents a time of day. The cards are passed through a scanner arrangement. The scanner output is used to switch relays and control switches to add or delete distant channels during the programming day. The cards are not particularly simple to program and, additionally, can be scanned for only a day. After the card passes through the reader arrangement, it must be manually reinserted. An additional disadvantage of this switching scale arrangement is that the card is read continuously by the reader. If it is desired to remove the card from the reader and insert a new card, the switches controlling the signal applied to the cable television system will be affected, regardless of when the card is removed from the reader.
U.S. Pat. No. 3,366,731, issued Jan. 30, 1968, to Wallerstein discloses a cable TV system with manual switching to permit certain channels to be deleted and other channels substituted. This system allows portions of the cable TV system to be provided with a different selection of TV channels.
Thus, there exists a need for a simple, inexpensive, reliable and easily programmed automatic switching device capable of switching one or more cable television channels to prevent duplication of television programming.