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 found in a 1999 documentation, but it can still be easily assembled today, as the...
This circuit, found in a 1988 documentation consisting of an audio switch that turns off the load...
Launched in 2016 but with documentation reviewed in June 2017, the Texas Instruments TLV854x...