This circuit was obtained from an Electronics Now from the 90's. It generates the dial signal and the ring tone, serving for testing as well as for demonstrations.
This sensitive touch key appears on this website from other sources. This version was taken from a...
This nonlinear gain circuit was found in a 1965 Electronic Design. The configuration can be used...
CMOS 4046 (PLL) is not very common. In this circuit it generates short pulses to excite a high...