We found this circuit in an American documentation from the 80s. The integrated circuits are operational amplifiers of the time. We can test modern comparators like the LM339.
The figure shows how to implement an alarm buzzer in an LM3914 to warn about crossing the scale...
This circuit can act as a shield being controlled by a microcontroller by pin 1 or 2. The...
This circuit was obtained from a 1980's QST magazine. The circuit can generate 1 to 15 MHz signals...