Abstract: A voltage controlled current source with variable compliance produces a load current through a load impedance where the load current value is substantially independent of the value chosen for the load impedance. The value of the current is substantially proportional to the difference between a first and second input voltage, and is substantially inversely proportional to a value of resistance chosen as a sense resistance. The current source comprises two variable gain instrumentation amplifiers and a resistance means connected in series with the load impedance.

Abstract: A circuit for interfacing switches to a component which allows the positions of the switches to be determined by the component. The component includes an input port and an output port. A switch network which is a parallel combination of two or more series combinations of a resistor and a switch is connected between the input and output port. A capacitor is connected between the input port and ground. The component determines switch positions by outputting a voltage on the output port and determining the time for the capacitor to charge to a predetermined value. Since each series combination has a unique resistance, the position of the switches therein can be determined in accordance with the capacitor charging time.