GB1426276A - Optical communication system - Google Patents

Abstract

1426276 Optical communication systems MATSUSHITA ELECTRONICS CORP 17 April 1973 [18 April 1972] 18562/73 Heading G1A An optional communication system comprises a light emitting semi-conductor device producing a pulsed output which is modulated with pulses at a selected one of a number of given pulse widths and a receiver including a light detector, a pulse reshaping circuit and an integrator which produces an amplitude modulated output a voltage value of which is representative of the pulse width selected. In Fig. 1, a GaAs IR emitting diode is used as the light source 1 and is pulsed by means of an astable multi-vibrator 2 the pulse width of which can be selected by a control 3 which may be a switch arranged to change a time constant determining component of the multi-vibrator. The radiation is detected by a phototransistor 4 and the pulses reshaped by a Schmitt circuit 5. The resulting constant amplitude pulses are converted into an analogue signal by an integrator 6 which may comprise a simple RC circuit. Alternatively, Figs. 2 and 4 (not shown), the integrator may comprise a staircase waveform generator which is reset after a predetermined number of input pulses as counted by a frequency divider. The peak amplitude of the staircase depends on the pulse widths of the pulses generating it and is applied to a logic discriminator circuit utilizing two amplifiers and an analogue gating arrangement to actuate one of three relays depending on whether the input lies below, between, or above a pair of threshold levels, Fig. 5 (not shown). The system may be used for remote control of a radio or TV and mention is made of using multiplexed signals.