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 uses a JFET CA3140 operational amplifier to convert a low frequency sinusoidal signal...
This simple receiver with junction FET uses a high impedance magnetic earphone (over 2 k). Power...
This is a project that can easily be adapted for other purposes such as counting people, objects,...