This tone recognizer circuit that relies on R5 and C1 was found in the December 1994 issue of Electronics Now. The circuit operates on voltages from 6 to 12 V typically.
In the figure we have a converter that generates a negative voltage from a positive voltage...
We found this circuit in an old optoelectronics manual from Texas Instruments. However, more...
The integrated circuit used in this project is not the most common. The use of a crystal...