Scientific Technology, Inc.

Roger M Brown

A system sensitive to light pulses which are substantially synchronous with a selected pulsed light source containing frequency components within the pulse which are above a predetermined frequency. A signal for exciting the selected pulsed light source is frequency modulated and connected to an AND gate as well as to the pulsed light source device. The pulsed light is received and conditioned producing a received signal which is also connected to the AND gate. Gate output occurs only during the period of time the received signal is in time coincidence with the frequency modulated pulsed light source excitation signal. Additional light pulses transmitted in the immediate area of the receiver by additional light pulse transmitting devices having frequency components within the light pulse above the predetermined frequency may be sensed by the receiver, but will not produce output at the AND gate unless in time coincidence with the frequency modulated signal. An occasional pulse or several pulses from the additional light source may, by chance, fall partially in time coincidence with the frequency modulated signal thereby producing one or several AND gate outputs in sequence. A step-charging filter receives the AND gate outputs requiring a predetermined number of sequential AND gate outputs to reach a predetermined filter output signal level. Thus the frequency modulated signal and the received signal must be in time coincidence for the predetermined number of sequential received pulses before the charging filter produces an output which initiates the system output. In this fashion a plurality of proximate pulsed light sensitive systems may operate with each system having a unique instantaneous transmitted light pulse frequency modulated phase by which associated receivers may discriminate between light pulse sources.

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Mountain View, CA, United States of America

Roger M Brown