This interesting reflex receiver used a different component, which at the time was showing up. The receiver is from a 1924 documentation and used a sodion tube.
Using the Linear Technologies LT3080 IC we have a constant current source with a 10 V voltage...
This sensor circuit for currents of the order of nanoamperes was found in an American...
Found in an 80's Elektor, this circuit can use any equivalent optical coupler. The buzzer is of the...