Using an operational amplifier, this circuit from a 90s Popular Electronics, is characterized by its high sensitivity. R5 can be added to control the gain.
This filter, from an audio publication from 1977, passes the frequency range corresponding to the...
In the figure we have three voltage doubler configurations that can be used in high and low...
This circuit was found in Motorola documentation from 1966. The lamps are according to power and...