This filter for frequencies from 300 Hz to 3.4 kHz was found in the February 1995 Radio Electronics magazine. Other operational amplifiers can be experimented, and the source must be dual.
This metal detector circuit uses an AM radio as an indicator. The radio is placed off-station and tuned...
This circuit was found in an Electronic Design. It makes use of a relaxation oscillator to trigger...
We found this circuit in an old American documentation. The operational amplifier is not common...