Voltage comparison

How is it posible to compare 4 voltages, so I can get an output from that one of them which is highest?

Try diodes.... put one diode in each input (anode to input) and connect all cadodes, only the highest voltage will be present, and diodes will prevent it from charging other inputs. Use Opamp to provide more current to your load and to reduce diode forward voltage.

It would be nice to know exactly what you're wanting to do here. Use the highest voltage to do something? Make a measurement of the highest voltage? It can be as simple as a diode or it could be as complex as a series of four comparators and some extra logic driving an analog data selector.

Dean

Or use PIC with ADc, that pretty easy too..