4-digit linear converter of weak currents electrometric module

The task was to design an easy-to-use and portable device used for a training course (e.g. for test measurements of p-n junction back current, I/sub /spl infin// of bipolar transistors, FET gate current, etc.). The device represents a portable adaptor to the digital voltmeter, designed as a module and a portable mains-operated power supply. It can also be powered by a self-contained source (two dry batteries with voltage 9 V). The modules can have 3 modifications.