This circuit was obtained from an Electronics Now from the 90's. It generates the dial signal and the ring tone, serving for testing as well as for demonstrations.
Found in documentation from the 90s, this circuit can employ other comparators in the series such as...
This circuit was found in a PE Hobbyst Handbook from 1992. The second oscillator is a VFO. The...
This motor control using transistors was found in a recent English publication. The circuit is for...