For analog lines, this circuit was found in the August 1994 issue of Electronics Now magazine. The transistors are common general-purpose types.
This basic configuration of voltage regulator using operational amplifier and zener was found in a...
This 75 W power supply was found in American documentation from the 1980s. Transistors can be...
This circuit was found in a 1987 magazine. It measures the pulse rate produced by a cardiac...