This Linear Technology circuit can measure currents from 100 pA to 100 uA. The circuit is from the 80's, using a component of the era. Transistors are general purpose types.
This PWM control circuit was found in an old documentation, but appears elsewhere on this site...
a We find this circuit which has a traditional configuration in a 1988 publication. The circuit is...
Indicated for applications with a PC, this circuit was obtained in an English publication in 1992....