In the diagrams below, the load under controlled is the LED. The Input (+5V) pin can be connected to a switch or the output pin of Arduino.
The load can be replaced with a BJT transistor, a MOSFET, etc.
Determine the value of the resistor that connects to pin 1
The forward current of 60mA is the max you can feed into the led without damage. The more current you feed into it the harder and faster it will turn on the transistor inside the opto. You dont need 60mA, 5 ~ 20mA is perfectly fine for what your doing.
When 1K resistor is used: I = V / R = 5V / 1000 = 5mA.
When 220 resistor is used: 5V / 220 = 22.72mA.
Note,
The reverse voltage is a limit for voltage around the wrong way that will damage the diode. As long as the voltage is applied in the forward direction (to light the led) this parameter can be ignored.
Maximum voltage that can be applied to the output end
When using opto-transistor as a switch, the load is on the collector and the emitter. Although the absolute maximum collector emitter breakdown voltage is DC 70V, it's better to keep the voltage below DC 30V as stated in the datasheet to avoid possible damage to the opto-transistor.
Most of the time when an opto-transistor is used, the base of the opto-transistor is left unconnected, so the emitter-base breakdown voltage can be ignored. But if it's used, the voltage must be smaller than 7V. Since transistor turns on at around 0.7V you really never need to put anything like 7V into their base.
Maximum current that can be applied to the output end
(Excerpt from 4N25 Datasheet)
For 4N25, the maximum collector current is 50mA.
For higher current application, 4N32 which supports 100mA collector current may be considered.
(Excerpt from 4N32 Datasheet)
Since the collector current is quite small, it's better to use 4N25 / 4N32 to drive a transistor, MOSFET , or a relay and have them handle the large current.
References:
4N25 Datasheet
http://www.vishay.com/docs/83725/4n25.pdf
Optoisolator 4N25 understanding the datasheets
http://www.eevblog.com/forum/beginners/optoisolator-4n25-understanding-the-datasheets/
4N25 Optoisolator Limits?
http://forums.bit-tech.net/showthread.php?t=55507
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