This circuit appears at various points on this site and in this section and can be designed with almost any operational amplifier. This version is from an American documentation from 1975.
This circuit was published in an English magazine from 1980. The magazine no longer exists, but...
Found in a 1990s Motorola documentation, this high voltage circuit uses a PUT that is not a common...
This proximity sensor was found in a 90s Popular Electronics. The base is a PLL567 that operates...