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 trips when a negative pulse is applied to its input or when the voltage drops below a...
This is an old 1988 circuit consisting of a timer or time control for exposing silk-screen arrays. The...
This circuit was taken from an old American documentation. It can be built with modern op amps. The...