This 555-based circuit was found in the August 1976 issue of Radio Electronics magazine. The tone frequencies are provided by the capacitors connected to the 555 IC.
This circuit is characterized by its low input impedance and voltage gain below the unit. The...
The circuit shown in the figure makes use of an LM3909, a low consumption and low voltage IC. The...
This receiver was obtained in a documentation from the 90's and is of the super-regenerative type....