This variable filter circuit was found in July 1975 Radio Electronics magazine. The circuit uses 3 general purpose op-amps like the 741 and must use a symmetrical source.
The circuit presented may use any general purpose transistor. The indicator is an LED and...
The operational amplifier used in this project no longer exists, but the circuit can be adapted to...
This car battery monitor was featured in the January 1988 issue of Radio Electronics magazine. The circuit...