This circuit uses a parallel resonant crystal to control the frequency. The circuit is from Radio Electronics magazine, February 1993. Equivalent transistors can be used.
This Vox or sound activated relay was found in an American documentation from 1975. Equivalent...
This circuit is from Motorola's Linear Interface ICs from 1993. The circuit uses a booster...
The existence of field effect transistors at the input of the integrated circuit (operational...