This circuit recognizes a tone determined by the tuned input circuit (R3 / R4 / C2). The circuit was found in Radio Electronics from the 90s. The 4046 is not a common component today.
This circuit of a Popular Electronics from the 90s makes use of components of the time. The...
The circuit shown in the figure can be useful in cases where a common telephone extension is used....
Found on an Elektor from the 90s, this TTL circuit generates a predetermined number of pulses with a...