Optoisolator TLP521

Hi all,
I have a simple question: I would like to use an optoisolator to control some devices from digital output of arduino board. In my case optoisolator is a TLP521, can I connect directly digital output to anode and cathode to gnd or I have to use a resistor between digital output of arduino and anode of TLP521?

many thanks
Fabrizio

Ciao Fabrizio

You should use a 270 ohm resistor from one of the arduino pin and connect it to the anode of the optocoupler
the cathode is connected to ground.

massimo

Grazie