Isolating inputs to Arduino (OptoIsolator etc)

Other Hardware Sensors
1

For one of my projects im looking at isolating some inputs to an Arduino. The digital inputs are either 12v or 5v and so i was going to use a 4N25 opto isolator for the isolation portion.
Am i right in assuming that the LED that they use in these packages behaves the same as a standard LED and that 470ohm and 150ohm resistors would be ideal for 13v and 5v respectively?

Secondly how should i run the Arduino? Just feed 5v off the Arduino into the Collector, and then connect the Emitter to the digital input on the Arduino? Or should i change it around so its not a floating input on the Arduino?

Also, im planning on having a few 0-5v analog inputs as well as the digital inputs. Is there any easy way to isolate those inputs? or should i just run them straight from the devices?

2

Search for "4N25 datasheet". It will give the specs and example circuits.

3

Just feed 5v off the Arduino into the Collector, and then connect the Emitter to the digital input on the Arduino?

No.
Collector to the digital input. Emitter to ground, and enable the internal pull up resistors.

4

Also be sure the signal that will be driving the input to the opto can supply the 20ma current (or whatever current you set via resistor size). Most optos will work fine at 10ma input.

Lefty