Abstract: A method and apparatus, of producing an alarm or ringing signal by providing a first pulse signal having a predetermined pulse width to define an alarm or ringing signal amplitude, and modulating the pulse signal with a second pulse signal having a pulse rate at least an order lower than the frequency of the first pulse signal to define the alarm or ringing signal frequency, averaging the modulated first pulse signal in a loudspeaker voice coil and reproducing the result in the loudspeaker to provide the alarm or ringing signal.

Abstract: A system for monitoring and controlling distributed functions within a building, such as the pressure and temperature of gases stored within cylinders. A plurality of modules are located at strategic points within the building for performing specific allocated functions in relation to monitoring and controlling the status of the gas cylinders. A first type of module detects dangerous conditions within the gas cylinders and generates and displays alarm signals in response thereto. A second type of module displays the alarm signals at a location remote from the gas cylinders and transmits command signals for remote shut off of a predetermined one or more of the gas cylinders. A central module interconnects each of the first and second modules and controls signal transmission therebetween.

Abstract: A self-adaptive computer memory address allocation apparatus and method for detecting the presence of memory chips connected to predetermined memory banks of a plurality of memory modules in a computer system, receiving and remapping address signals, and contiguously enabling the predetermined memory banks in response thereto. A programmable logic array generates enable signals for enabling the predetermined memory banks of the memory modules in response to receiving address and control signals from a main controller. The remapping process is performed during power up such that no wait states are introduced during subsequent memory accesses.

Abstract: A DC control circuit for limiting metallic and longitudinal currents flowing in a balanced telephone line, and maintaining a predetermined DC bias voltage on tip and ring leads of the balanced line. A negative feedback path is established for monitoring voltage on the tip lead, comparing the monitored voltage with a predetermined offset bias voltage and generating a DC signal for application to tip and ring driver circuits for application to the balanced line in response thereto. Longitudinal and metallic currents are detected in a further pair of differential amplifiers for generating further DC signals such that a voltage corresponding to the detected longitudinal current is generated and applied to the tip lead, whereby a first one of the further pair of differential amplifiers adjusts the generated DC bias signal for limiting the longitudinal current flowing in the tip and ring leads.

Abstract: A digital loudspeaking telephone for connection to a telephone line, including a microphone, speaker, codec and digital signal processor. Incoming and outgoing signals are received by the digital signal processor from remote and local subscribers via the telephone line and microphone respectively. The processor generates and compares incoming and outgoing envelope and noise floor signal levels derived from the received incoming and outgoing signals and in response suppresses a particular compared, and one of the incoming or outgoing signals. Automatic gain control of outgoing signals is implemented in order to allow smooth switching of the outgoing signals and to suppress background noise from being transmitted by the microphone. Room echo and reverberation are also detected, and the processor eliminates spurious channel switching due to the detected echo signals.

Abstract: A trunk circuit is disclosed for coupling a bidirectional lead pair, such as balanced tip and ring leads, to a pair of unidirectional leads such as unbalanced input and output leads. The trunk circuit incorporates a small inexpensive transformer for effecting this coupling and for providing large common mode signal isolation and correct longitudinal balance. Circuitry is provided for matching the nominal balanced AC and DC line impedances. The trunk circuit also provides circuitry for generating dial pulse signals under control of a microprocessor or other external controller.

Abstract: A chemical vapor deposition apparatus for depositing films or coatings on semiconductor substrates. Substrates are supported within an air tight reactor and heated to a predetermined reaction temperature. A manifold disposed within the reactor, and having a plurality of openings therein, receives one or more reactive vapors and evenly distributes the vapors through the openings in the vicinity of the substrates, such that the vapors react at the substrate surfaces and a film or coating is deposited thereon. One or more cooling tubes substantially envelope the manifold, thereby maintaining the manifold at a temperature less than at least the reaction temperature such that the vapors do not prematurely react within the manifold. Hence, films and coatings are prevented from forming within the manifold, and sufficient unreacted vapors are supplied to the substrate to effect a satisfactory coating or film thereon.

Abstract: An LED driver circuit including a current source for generating constant drive current to a plurality of series connected LEDs, circuitry for selectively enabling and disabling predetermined ones of the LEDs and further circuitry for disabling the current source in the event none of the LEDs are enabled. The LED driver circuit is of simple design and low cost, and is characterized by low power consumption due to the current source being disabled in the event none of the LEDs are enabled.

Abstract: A circuit for detecting a first plurality of status signals on a multiplicity of telephone lines and generating a second lesser plurality of control signals, less than the first plurality, in response thereto. Predetermined ones of the control signals are transmitted via a multiplexing circuit to a comparator circuit. A digital-to-analog converter generates analog threshold voltages for application to the comparator circuit in response to receiving command signals from a microprocessor. The comparator circuit generates a third lesser plurality of output signals, less than the second plurality, indicative of the status of a multiplicity of remote trunk circuits connected to the telephone lines. The circuit is inexpensive and occupies little circuit board area.