Quote:
Originally Posted by Ether
The turn-on threshold is 1.6ma max. The silicon drop across the LED is approx 1.2V at 3ma. There's a 150 ohm series resistor.
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So a 5 volt signal will yield about 25 milliamps. That's nearly a factor of sixteen greater than is required (and a lot higher than I expected*). A 3.3 volt signal gives 14 milliamps, indeed approximately half of the "nominal" 5v value. But half of a 16-fold input is still an 8-fold input, which will definitely work.
With the low 150-ohm series resistor, even a 1.5 volt input ought to be able to turn on the opto-isolator.
* The circuitry I'm used to has 1.2k series resistors on optocouplers, giving about a 2x "safety factor" for turnon current with a 5v control signal, and limiting the current to ten milliamps in case of accidental application of automobile battery voltage. 3.3 volts isn't quite enough to be certain of having it work in that case.