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### Topic: [help!] advice on an optocoupler array (Read 1 time)previous topic - next topic

#### dataplex

##### Nov 07, 2011, 03:46 pm
i am building a switch board with twelve 4n25 optocouplers, to be controlled by my arduino.

i intend to connect each digital pin of my duemilanove to a 220 OHM resistor and then into the led anode. cathode goes straight to ground.

i am not sure about the amperage of the couplers, but here is the datasheet :: http://www.vishay.com/docs/83725/4n25.pdf

so, my question is: is it safe to connect all these couplers to the digital pins at the same time? will it fry my chip?

thanks!

#### JChristensen

#1
##### Nov 07, 2011, 04:15 pm
Most of the test conditions in the datasheet specify IF = 10mA, and typical VF is 1.3V, so Mr. Ohm says R = V/I = (5 - 1.3) / 0.01 = 370?. So 220? may be a bit smaller than needed, I might try 330?, and then measure the current (or the voltage across the resistor, and calculate the current) and of course also see how it works.

Maximum current into an ATmega328 is 200mA, so twelve 4N25s at 10mA each should be around 120mA, but of course any other loads will have to be added to that.

#2