This circuit protects the speaker from dangerous direct currents that could damage it. The circuit is from an Electronics Experimenter Handbook 1993 edition.
The oscillator shown in the figure generates a 1 kHz tone that is reproduced on the speaker with...
In the figure we have the photo-conductive way of using a photocell to control a small motor with...
This circuit was found in the June 1991 issue of Radio Electronics magazine. The circuit uses two...