This circuit from the 80's makes use of two transconductance operationals of the time. Modern equivalents can be used. The circuit does not need to be powered by a symmetrical source.
This circuit marks the number of minutes of a telephone call on a display, starting when the...
This circuit was obtained from a 1966 General Electric documentation. It can serve as a basis for...
This is a change from the previous interface, also used an uncommon operational one today. The...