Found in a 90s Popular Electronics, it serves both TTL and CMOS logic. The injector can provide 10 kHz or 100 Hz signals. The circuit drives a transducer and two LEDs.
This circuit is from an 80's electronic component manual. It has the way to simulate an inductor...
This is the receiver for the previous circuit found in the November 1991 Radio Electronics...
This circuit was found in a Popular Electronics documentation from the 90s. It is possible to switch...