2-wire interface version 2.0

Reducing the number of interconnections in any system improves reliability. In June 2012 we published an idea by this author which uses just two wires instead of the more usual three to interface a switch and indicator light. The author has further refined the circuit to use less current and to make it compatible with controllers operating at a supply voltage of just 2.1 V. That should be reason enough to give this circuit a second look.