GB1425199A - Pulsed light type control system - Google Patents

Abstract

1425199 Optical control systems MATSUSHITA ELECTRONICS CORP 29 May 1973 [30 May 1972] 25337/73 Heading G1A In a system for transmitting information over a radiation path, a light source emits pulses of predetermined period and a light detector converts the pulses to electric signals which activate a group of monostable multi-vibrators whose outputs are combined by a logic circuit to give a signal depending on the period of the light pulses received. The light source may be an l.e.d. which radiates pulses whose period is either t 1 , or 2 t 1 , the detector then being connected to two multivibrators as in Fig. 3 (not shown). Fig. 5a shows the detector output, while Figs. 5b and 5c respectively show the outputs triggered from the two multi-vibrators. The first multi-vibrator produces a train of pulses of duration T 1 , slightly less than t 1 , while the second multi-vibrator gives pulses of duration 2T 1 . It will be seen that the output of both multi-vibrators is substantially D.C. because as soon as each multi-vibrator turns off it is triggered on again by the detector signal. In Figs. 6a, 6b and 6c the response of the two multivibrators to detector signals of period 2t 1 is shown, and here only the second multi-vibrator produces the substantially D.C. output. The multi-vibrator outputs are connected to terminals 7 and 8 of logic transistors in Fig. 4, and when both terminals receive substantially D.C. inputs relay 12 is operated, while when only terminal 8 receives such an input relay 13 is operated. Hence one or other relay is operated in response to the period of the signal transmitted by the l.e.d.