Is it possible to make the following with any of the arduino's?
1 input -> measure the voltage (AC 48-230V)
24 inputs -> detect if there is a voltage (AC 48-230V)
the 24 inputs i dont care what the voltage is, but i need to see if it is "up" with an AC input (the AC input can change depending on the state of the machine), but all i need to monitor is wether it is giving an voltage > 0V
For the 24 inputs, Opto Isolator is the correct solution for your purpose, as I can see a it is a AC supply of 48 to 230V, I suggest to use a bridge rectifier (400V) which gives you some sort of pulsating DC, the just use resistor for voltage drop, and connect it to cheap optocoupler from Vishay or Farichild. The transistor side of the optocoupler connect to 5V power supply on which your Arduino board can monitor it. You get a high when AC Voltage is present and a low when AC Voltage is not present.