This circuit is from an American documentation from 1975. The circuit uses components of the time which can be replaced by modern equivalents. The coupler is homemade with a lamp and a photocell.
The oscillator shown in the figure generates a 1 kHz tone that is reproduced on the speaker with...
This circuit makes use of a 741 single source operational amplifier to measure resistors on a...
This analog frequency meter for low frequencies was found in Radio Electronics magazine from July...