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.
This circuit was found in an old Poptronics but is still current as transistors can be replaced...
July 2017 - The new TLP240 and TLP241A optical couplers with MOSFET output, manufactured by...
This is one of the many versions of amplifiers with LM386. This was achieved in an old publication (1981). The...