Found in a 90s Popular Electronics, this circuit uses a 741 to generate frequencies from 0.1 to 30 Hz. Observe the phototransistor feedback.
In the figure we have the way to configure a control for incandescent lamps with full wave control...
This conventional circuit with a source adjustable to 1.5 A was obtained in a documentation...
This circuit turns your air conditioner or other appliance on and off in adjustable cycles to save...