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.
This circuit was obtained in the Philips integrated circuits manual of 1990. The indicated power is...
In the figure we show an application in which the 4093 excites a stage with 4 transistors in the...
This 1995 documentation circuit detects when an extension on a phone line is active. Adjustment of the...