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 long-time circuit uses a field effect transistor, which may be the BF245, and depends on a...
The figure shows how to implement the AND function with a Norton LM3900 operational amplifier. The number of...
This circuit is from an old documentation, but it can be elaborated with ease, since the...