Plotting projector

Claim 1

A plotting projector for displaying on a screen an historical and periodically updated trace representative of first and second parameters at least one of which changes with time, said projector comprising: a high intensity light source for forming a beam; electrically operable deflection means for causing said beam to be deflected to effect illumination of portions of the screen to which the beam is directed; timer means for releasing an initial timing pulse and subsequent timing pulses at predetermined intervals thereafter; sync signal generating means for generating an initial sync signal in response to said initial timing pulse, and for generating subsequent sync signals; first and second modulation means, responsive to said initial and subsequent sync signals for converting initial and subsequent samples of analog signals representing said parameters into the form of initial and subsequent data words; recording and playback means for storing in serial form said initial and subsequent data words and said initial and subsequent sync signals, and for playing back thereof at a repetition rate above the flicker rate for a viewer of said screen; first and second demodulator means for demodulating each playback of said data words to form deflection signals for driving said deflection means; logic means, responsive to each of said subsequent timing pulses and to the end of a playback of the last sync signal of the recorded series thereof, for causing said sync signal generator to produce the next of said subsequent sync pulses in timed relation to the repetition rate of said recording and playback means so that said next subsequent sync signal is recorded in series with and immediately following said last sync signal, and the corresponding subsequent data word outputs of said modulator means are recorded in series with and immediately following those already recorded to cause the recorded data words and sync signals to accumulate in said recording and playback means and the repetitively projected trace to be periodically updated; means for generating beam control signals to cause said beam to illuminate said screen only from a predetermined time in each playback of the accumulated series of data words to the end thereof; said modulation means comprising pulse position modulation means for rendering said data words as pulse position words, the lengths of said data words being equal to the lengths of Said sync signals; said sync signal generating means comprising a one-shot multivibrator for providing said sync signals of predetermined length; means for providing an end of playback signal in response to the end of the last sync signal in the recorded series of sync signals; delay means for introducing a delay in said end of playback signal; flip-flop means responsive to each of said subsequent timing pulses to shift from a first to a second output condition; and AND gate means responsive to each coincidence of said second output condition and said delayed end of playback signal to render an output for triggering said one-shot multivibrator to generate one of said subsequent sync signals.