Found in a 90s EDN, this circuit is indicated for power control through a 4-20 mA line. The circuit makes use of optical couplers of the time.
This transmitter modulator amplifier for the 11-meter band (CB) was published in Radio Electronics...
This oscillator, which operates from 2 V, was found in the June 1993 issue of Radio Electronics magazine....
This amplifier for electrometer can work with currents of 0.1 pA in a band of 1 Hz. The circuit is...