This circuit is from the Motorola Linear Databook of 1990 and can be implemented with other operational amplifiers. The power supply must be symmetrical.
In the figure we have the way to linearize the response of a TTL port with the use of a feedback...
November 2016 - The TL3780 ultra-miniature E-switch touch switches can now be obtained from Mouser...
This circuit is from a 1967 US publication. The configuration can serve as a basis for designs...