This 9-pixel circuit has been implemented with 9 LDRs and can be coupled to a processing system for an elementary artificial eye. The circuit is from Radio Electronics, November 1986.
Figure bellow shows another circuit that allows adjustments in the duty cycle of the output...
This circuit is from an American publication of 1978. It can be assembled with modern transistors, since...
Found in a documentation for radio amateurs from the 90s, this circuit is suitable for RF...