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[on:]

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!

[Reply #1 on:]

Most of the test conditions in the datasheet specify I_F = 10mA, and typical V_F is 1.3V, so Mr. Ohm says R = V/I = (5 - 1.3) / 0.01 = 370Ω. So 220Ω may be a bit smaller than needed, I might try 330Ω, 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.

[Reply #2 on:]

hi, thanks for the reply!

so using the 220 ohm resistors i would be at risk of frying the arduino? or perhaps only if ALL optocouplers are triggered at once?

and -how do you mean, into the atmega?