This lockable two-position servo control system was found in documentation from the 1990s. The error amplifier can be an operational amplifier and the sensors are phototransistors.
This LM139, 239, or 339 comparator configuration appears elsewhere in this site and this section....
Although it is a common configuration today, these circuits were taken from an old publication. The...
This circuit is from a 1979 publication. The sensor consists of plates or screens that, when...