We found this circuit in a 90s Radio Electronics. The circuit generates frequency-modulated 220 kHz signals. The components used are still common.
This circuit visually indicates that a high voltage is present in an outlet or other point. The...
This circuit found in a 1988 documentation consists of a timer or sequential timer controller. The...
Using a 4017 as a base, this circuit from a 1990s Popular Electronics generates low-frequency...