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.
Oscillators up to some megaherts can be made with comparators like the LM139, 239 or 339. Theses...
This circuit is regulated by zener and provides a voltage of 9 V. The circuit is from a Radio...
We find this circuit in a 1973 technical documentation. Common transistors may be BC548 and FET or...