The circuit shown is from Motorola's 1990 Linear Databook. Shaded components are optional. The characteristics of the coils are given next to the diagram.
This circuit was obtained in an old documentation, but it is still current by the used components....
This circuit makes use of a transconductance operational amplifier. It generates signals with TTL...
This circuit is from a 90s Popular Electronics. The transistors are of general use and the buzzer...