This circuit is from the 80's, using an integrated of the time. The circuit serves as a reference, as this type of dialing is no longer used today.
This heartbeat sensor circuit was found in the July 1992 issue of Radio Electronics magazine. The...
This amplifier circuit with a low power MOSFET was found in Popular Electronics from the 90s. The...
This circuit, which can be built with several CMOS gates, was found in the March 1996 issue of...