Found in a 1980s manufacturer documentation, this circuit can be used as an optical shield. The integrated circuit is from the era and modern equivalents can be tried out.
This circuit was published in an English magazine from 1977, but it can be easily assembled since...
We found this circuit in an Electronic Design. The main integrated circuit is the 4017. The...
Found in the 1990 special issue of Radio Electronics Experimenter magazine, this circuit uses an...