Found in a PE Hobbyst Handbook of 1991, this circuit was originally proposed to time photographic baths in developing rooms but can be used for other purposes. The circuit beeps at 30-second intervals.
This traditional version of a double time constant dimmer using triac is from the 90s...
Operating in the range of 1.5 to 15 kHz, this sinusoidal oscillator is based on a 741 operational. The...
This circuit with only two transistors is from an 80's EDN. It can be implemented with two current...