AB=LED, 00=OFF, 01=OFF, 10=ON, 11=OFF. A logic AND gate, and a logic INVERTER put together to make the respective +/- input the only allowed. Note: You can run the logic directly to the 4+ and remove the 4v or use the +4 as the logic and get rid of the +logic, as well use the -4 for the -logic, and get rid of that logic too. The circuit is universal somewhat like that. and is about inputs being managed. - nforystek
