This interesting circuit found in American documentation generates a busy signal, without you having to take the phone off the hook if you do not want to answer. The components used are common.
The circuit shown in the figure is suggested by ON Semiconductor (www.onsemi.com), based on its...
September 2016 - can be found at Mouser Electronics the new amplifiers with digital variable gain...
This simple 1-transistor audio preamplifier appeared in the June 1968 Radio Electronics magazine. The...