user71568: I am making a shutter for my camera using a Arduino and an optocoupler.
I understand most of most parts, but unsure about the resistor because I don't have the correct size. 5V will be coming from the Arduino, and the 4N35 will need 1.3V 10mA. This leads to a 380Ω resistor.
Now I only have 100Ω, 220Ω, 330Ω, and 1kΩ resistors. I have read I shouldn't use anything lower than 380Ω and only use higher but 1kΩ seem a little too high haha.
Just looking for some pointers please.

user4143: 1kΩ will be just fine. But if you want lower you could take two 1kΩ and place them in parallel - that will give you 500Ω.
BTW - 1kΩ will give you ((5-1.3)/1000=) 3.7mA through the diode of the optocoupler, and 500Ω will give you ((5-1.3)/500=) 7.4mA.

user521: And 330 will give you just over 11mA, I'd go with that

71568: <p>I am making a shutter for my camera using a Arduino and an optocoupler.</p>
<p>I understand most of most parts, but unsure about the resistor because I don't have the correct size. 5V will be coming from the Arduino, and the <a href="https://www.vishay.com/docs/81181/4n35.pdf" rel="nofollow noreferrer">4N35</a> will need 1.3V 10mA. This leads to a 380Ω resistor.</p>
<p>Now I only have 100Ω, 220Ω, 330Ω, and 1kΩ resistors. I have read I shouldn't use anything lower than 380Ω and only use higher but 1kΩ seem a little too high haha.</p>
<p>Just looking for some pointers please.</p>
 4143: <p>1kΩ will be just fine. But if you want lower you could take two 1kΩ and place them in parallel - that will give you 500Ω.</p>
<p>BTW - 1kΩ will give you ((5-1.3)/1000=) 3.7mA through the diode of the optocoupler, and 500Ω will give you ((5-1.3)/500=) 7.4mA.</p>
 521: <p>And 330 will give you just over 11mA, I'd go with that</p>
