With this circuit it is possible to use a frequency meter as a tachometer. The circuit was found in American documentation from the 90s. The phototransistor can be of any type.
Found in September 1984 Radio Electronics issue this circuit has adjustable pulse width and...
This low power circuit for the FM band was found in a spy book from the 90s. The tunnel diode is...
This circuit was found in a 1987 edition of the United States' Hands On Electronics magazine. The...