This two-tone decoder has a bandwidth of 24%. The circuit is from a 1994 Electronics Now. The components without the value determine the recognized frequency.
This circuit uses an LDR as a sensor to trigger an LED indicator at a preset lighting level. The...
We found this circuit in an American publication from the 80's translated into Portuguese. The...
We found this circuit in an old French documentation from the 70s, but it can be assembled using...