This circuit is from 1999 documentation. The integrated circuit used is not very common today. Both transistors are used if the motor current is greater than 500 mA.
Found in a Hands On Electronics of the 80s, this circuit makes use of a gas sensor of the time....
This control for a heating element was found in an old documentation. The current in the element...
This variable gain circuit for analog video signals was found in a 90s Linear Technology...