I have a Arduino uno 3.
Using a 4N33 opto isolator, when I connect pin 1 to +5V and connect pin 2 to GND, the Arduino indicator light go dim.
please advise.
You're connecting an LED across 5V with no current limiting resistor?
You need a 220 Ohm resistor to the LED.
Thankyou. I did not know that an opto required a limiting resistor.
What might be a good value?
Working fine now. Thanks.