1. Field of the Invention
This invention relates in general to certain new and useful improvements in a modified form of half duplex voice communication system having a pair of speaker-microphone combinations and which control over the generation of sounds in a link between the two microphone-speaker combinations is dedicated to a party using one such combination and not the other.
2. Brief Description of the Prior Art
Private telephone links between a secured area or an enclosed environment and an unsecured area or external environment, or so-called "exterior environment", have been widely used in recent years for purposes of security and the like. For example, in controlled access apartment buildings or homes, someone wishing to gain access to the grounds of that apartment building or home must first call an occupant of the apartment building or home through a telephone link. A telephone handset may be located in the external environment or outside of the building and a telephone handset in the apartment or home can be switched into communication over a telephone line, which may be a private intercom line A conventional dialer and buzzer arrangement is typically employed in these systems.
In recent years, due to the tendancy of handset theft and other forms of vandalism, many security buildings and limited access buildings and other security and limited access environments have attempted to replace the handset, at least in the external environment with a combination speaker- microphone arrangement. This speaker-microphone arrangement is typically mounted behind a shield or screen within a wall in order to reduce a potential for theft or vandalism.
There are many attendant problems to the use of the speakermicrophone arrangement. These systems are typically operated on the full duplex principle, that is, the microphone receiving the noise, which may be spoken communication, will exercise control over the line. Thus, for example, if the party in the relatively quiet environment, such as the apartment or home, is generating sounds over the voice communication link, that party will maintain control over the voice communication link until such time that he or she stops talking. In like manner, if the party in the relatively noisy environment, who may wish to gain access to the building or controlled area, for example, is speaking over the voice communication link then that party will generally maintain control over the link until such time as he or she has completed talking. The telephone handset or other speakermicrophone combination in the external or exterior environment is generally in a relatively noisy environment. The noise background in the external environment is variable and can range from being slightly relatively quiet to excessively noisy in a relatively short time period. The telephone handset or other speaker-microphone in generally a relatively noise free environment.
A significant problem arises in conventional voice communication systems if there is any substantial background noise. When the user is not speaking into a handset and substantial noise is in the background, there is effectively no discrimination between the users voice and the background noise. Consequently, background noise can interfere to a point where the outside or external telephone will maintain complete control over the line to the exclusion of the party at the other end on the inside of the apartment or in some other relatively noise free environment. Thus, these systems have been relatively ineffective in certain areas.
In telephone communication links, the speaker in the handset is sufficiently distant from the microphone so as to eliminate any significant feedback problems. Even with the so-called "telephone speaker system" or so-called "squawk box", when the speaker is located a sufficient distance from the microphone, there is still little or no feedback problem. However, in the conventional hands-off telephone access line, which utilizes a speaker-microphone combination, generally mounted in very close relationship, the feedback problems become quite acute.
Recently, the half-duplex system has been used to obviate the aforesaid problem on the theory that both parties do not talk at the same point in time. In the half-duplex system, the circuit is designed to monitor the line and determine the source of a sound signal which may be a voice signal. Thus, if the party in the interior or relatively noise free environment is speaking, that party will have transmit control over the line until he or she stops talking, In like manner, once the party in the external or relatively noisy environment starts talking, that party will transmit until he or she stops talking. Again, the problem arises where there is a source of background noise in the external environment. This source of noise in the background could constantly keep the external phone in the transmit mode thereby precluding the party in the interior environment from speaking at all.
The present invention obviates these and other problems in the provision of a voice communication system in which a microprocessor circuit monitors the telephone line to determine the existence of signals on that telephone line. The microprocessor is designed to provide transmit control to the party in the generally interior or relatively noise free environment and thereby only permits transmit control to the party in the external or relatively noisy environment when the party in the interior environment is not transmitting voice signals.