This shield circuit with an optical coupler was found in an 90s EDN. The circuit can be used with voltages from 0 to 600 V with the indicated component values.
This circuit can serve as a basis for a digital mixer or simply for a noiseless switch of audio...
This traditional mixer configuration with a high input impedance was found in a 90’s Popular...
This medium wave radio works with any general purpose NPN transistor. The diode must be made of...