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 is from a PE Hobbyst Handbook from 1991. The integrated circuit is a common 555 and...
The configuration below is suggested by the National Semiconductor Linear Applications Handbook. The...
Other series operationals such as the LM258, LM358 and LM2904 can be used on this circuit of the...