With this circuit it is possible to vary the resistance by adjusting the mark/space reaction of the 555. The circuit was found in the November 1989 Radio Electronics magazine.
This 80's circuit has been winning. It is a 1 000 gain sample and hold circuit and an offset...
The purpose of this 1-transistor amplifier is to allow the use of a milliammeter in an application...
We found this circuit in an old General Electric documentation. In fact, PUTs are not common...