Arduino Mega 2560 - Stepping down voltage as input
You are saying you need to step down the voltage, but then you are describing the voltage levels as if they range from 0 to 5 volts. Is the voltage range of your signals 0 to 5V? If yes, then you can used the A/D converters that are built into the AtMega2560. If you have more inputs than supported by AtMega2560, you can use an analog switch, such as 74HC4851. I don't know how the analog inputs are configured on the Arduino board, you might have to use Op Amp configured as unit gain as a front end. Also, you might want to use zener diode to limit the voltage to 5 volts.