If you are talking about less than 5V you can connect it directly, but I recommend using a series resistor and it's not a bad idea to add a capacitor for some filtering. Any resistor from a few K Ohms up to 100K should be good.
If you are talking about less than 5V you can connect it directly, but I recommend using a series resistor and it's not a bad idea to add a capacitor for some filtering. Any resistor from a few K Ohms up to 100K should be good.