This analog frequency meter for low frequencies was found in Radio Electronics magazine from July 1958. The circuit has several scales with the frequencies indicated in the diagram.
This circuit was obtained in an Electronics Now from the 90s. The circuit uses operational...
This circuit operates at a frequency around 1 MHz, having been found in a technical documentation from...
The TAA131 used in this circuit is not very easy to find today, but an equivalent low power audio...