I want to connect one of my Arduinos to some old analogue hardware, which has a number of sensor wires running at 12V. I just want to read and analyse the signal on Arduino. I'm wondering what I need to do to make this safe for the 5V inputs.
Would it be right to assume that just reading an analogue input will have a fixed power draw (40mA?) and therefore use Ohm's law and a single resistor (per pin) to bring the 12v down to 5v? Or should I be looking at a linear regulator or a buck converter etc? The simpler the better because I have about 20 pins to read!