The cut-off frequency of the circuit shown in the figure is 750 Hz, with the components used. The circuit applies to almost any operational amplifier and the power supply must be symmetrical.
The circuit shown in the figure below is suggested by ON Semiconductor (www.onsemi.com), based on...
This control is intended for 110 VAC or 220 VAC Motors. Any TIC series triac can be used according the power...
This circuit was found in a 1999 English magazine, but can be easily assembled with BC548...