Square wave keying ratio indicator - has LED display on change of ratio applicable as check to control system using variable ratio

摘要

The circuit is for the display of the keying ratio of a rectangular wave voltage, with changes and direction of changes in the ratio, especially for application in control systems using keying ration changes to control an analogue function, such as an ultrasonic remote control system for a television receiver. The voltage is first fed to a first integrating RC element (R1, C1) which is followed by a differentiating second RC element (R2, C2), the input of which is passed to one input of a differential amplifier (DV) with tis other input held at a fixed potential. Two light-emitting diodes are connected in parallel across the output terminals of the amplifier.