Found in a Popular Electronics from the 90s, it applies to the old answering machines that used tapes. It emits a warning beep on the drive.
The circuit shown enables dynamic diode testing with an oscilloscope. We found this configuration in a...
The circuit shown in the figure is quite interesting in control and alarm applications. This...
This different power control circuit with SCR was obtained from a 1967 magazine. The SCR can be...