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 a stereo decoder from the 70's with pilot lamp for signal indication. The...
This circuit was found in an Elektor from the 90s. It makes use of digital CMOS integrated devices...
We found this mains-powered switch circuit in Electronics Now magazine from July 1994. It could be...