This circuit was found in General Electric's 1965 documentation. It appears elsewhere on the site. The SCR and the diodes must be in accordance with the motor current.
The sensor for this Intersil circuit (1983 databook) is a common silicon transistor. The trimpot...
This circuit is from a 1972 Motorola publication. The used transistor can still be found, but it...
This is the simplest setting for lighting an LED. The circuit is from old English documentation that got...