Control system for audio-visual projector
AssigneeIndal Limited
InventorMichael G. Lee
Life of this patent
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Abstract
A system for the control, selection and synchronization of the movement of magnetic tape and filmstrip in a film projection system which may include a sound program. Film advance is synchronized with the sound reproduction by means of recorded signals on the magnetic tape which unambiguously specify the filmstrip frame number appropriate to the magnetic tape sound program. Means are provided to allow the operator to rapidly access a particular filmstrip frame by specifying its number. When a sound program is included, the invention assures automatic synchronization of the sound program with the filmstrip frame.
Claims15
A control system for an audio-visual device for sequentially projecting a plurality of frames of a filmstrip responsive to actuation of a film advance mechanism and for presenting an audio program recorded on an audio tape including spaced-apart coded signals each of which uniquely identifies a respective frame of said filmstrip so that each portion of said tape is associated with a respective film frame, said control system comprising:
- sync frame detector means for generating a reset signal responsive to projection of a predetermined sync frame;
- film frame counter means incremented responsive to actuation of said film advance mechanism and reset by the reset signal from said sync frame detector means such that a digital word at the output of said counter identify the frame being projected;
- tape decoder means receiving the coded signals on said audio tape and generating a digital word indicative of the film frame associated with the coded signal last appearing in said audio program;
- and
- comparator means for actuating said advance mechanism until the digital word at the output of said film frame counter means is equal to the digital word at the output of said tape decoder means whereby the frames of said filmstrip are advanced in synchronism with said audio program.
In an audio visual device for presenting an audio program recorded on an audio tape contained in an audio section of an audio-visual cassette and for sequentially projecting a plurality of frames of a filmstrip contained in a visual section of said audio-visual cassette, the frames of said filmstrip being incremented by an advance mechanism which is actuated by multi-frequency control tones on said audio program, a detector system for recognizing said control tones as the playing speed of said audio tape varies from a low speed to a high speed responsive to a high-speed command signal, said system comprising frequency discriminator means for generating an output voltage having a magnitude which is proportional to the difference in frequency between said audio program and a reference frequency, said reference frequency being shifted from a low-speed reference frequency when said tape is playing at said low speed to a high-speed reference frequency when said tape is playing at said high speed, the ratio between said low speed reference frequency and said high-speed reference frequency being substantially equal to the ratio between said low speed and said high speed so that the voltages generated by said frequency discriminator means responsive to said control tones are constant as the playing speed of said audio tape changes between said high and low speeds.
In a device for sequentially projecting a plurality of frames of a filmstrip, one of which is a sync frame having a light transmissibility which differs from the light transmissibility of all other frames, said device further including sync frame detector means for identifying said sync frame, comprising a mirror receiving an unfocused image from each frame as it is projected and reflecting said image to where it can be viewed, a relatively small portion of said mirror spread apart over a relatively wide area being light transmissive to allow a small portion of said image to pass through said mirror onto light-receiving means for generating a signal indicative of the intensity of said image, whereby a signal indicative of a relatively low intensity identifies said sync frame.
Dependencies are inferred from the claim text.