This circuit was originally intended for reading movie soundtracks. The circuit is from 1967 and was found in an English publication. The sensor is semiconductor type.
This circuit, used in radio communication, converts CW signals and tones that allow you to follow...
This is one of many possible configurations for this type of oscillator that generates sinusoidal...
When a pulse of light reaches the sensor [a CDs cell or LDR] the flip-flop changes its state....