My house is equipped with a wired alarm system that's missing the hardware controller board. Whats left is a number of sensors (NC) and the wiring to a central location. Cable lengths are anywhere from 3 to 20 meters. I would like to build a simple controller board using Arduino to read the sensor states. What would be the best approach, how would you wire the sensors to the controller board? I have tried to find the best approach online but I have seen many different solutions. I'm thinking of using a resistor in series with the sensor together with an optocoupler, feeding the sensor with 12 volt. Any ideas?