Found in Popular Electronics from the 90s, this circuit generates signals in a frequency range set to R7 and basically determined by C1. Operational and equivalent transistors can be used.
This circuit is from 1983 documentation. The author shows us an experimental circuit of a siren...
This simple circuit indicates whether at a point in the wiring of a car 12 V is present. The clip...
This oscillator employs a Motorola operational amplifier common in the 70s. We can implement the...