This small tone generator was found in the November 1987 issue of Radio Electronics magazine. The phototransistor is common and controls the sounds generated. The basic frequency is given by C1.
In the figure we have the adapter circuit for connecting a headphone to the output of a stereo...
Found in the June 1972 issue of Radio Electronics magazine, this circuit generates signals that...
The output of this circuit must be connected to the input of an audio amplifier. The microphone is a small...