[Noisebridge-discuss] Electronics Question

macegr garrettmace at gmail.com
Tue Sep 24 08:28:26 UTC 2013


33 ohms would be problematic. Max current is 50mA and 33ohms would try to push over 100mA through. But the uC pin max is about 40mA. So either the LED in the isolator fails or the Arduino fails (maybe not immediately, but soon). Datasheet recommends 5-10mA with operation down to 1.5mA so my original suggestion of 1K is fine.

The polarity reminder is spot on.


On Sep 24, 2013, at 12:43 AM, Jake <jake at spaz.org> wrote:

> phil,
> 
> did you try swapping the "output" pins of the optocoupler?  It is a photodiode in there (not a relay) so it does care about polarity i think.
> 
> it seems like you are being properly methodical, keep it up and you will succeed.
> 
> Your calculation of 33 ohms for the LED side of the optoisolator is probably fine, although 100 ohms would probably work just as well.  You are supplying 5V from the arduino, to an LED (maybe infrared in there) which takes maybe 1.8 volts, at 0.020 amp.  so 5v - 1.8v = 3.2v, and a resistor making 0.020 amps at 3.2v is 3.2 / 0.020 = 160 ohms.  Just my guess without looking at the datasheep.
> 
> what are you trying to make?
> 
> -jake
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