Found in an April 1977 Radio Electronics issue, this circuit uses the well-known XR2206. The C1 values for the various frequency bands are given next to the diagram.
This circuit is from an American publication from 1978 and can currently be assembled with minor...
This is a traditional double timer configuration with the 555 found in a 1987 documentation. The...
This circuit was suggested by National Semiconductor in its Linear Applications Handbook. The...