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Topic: Arduino Input 12v Opto-isolators (Read 2693 times) previous topic - next topic


Feb 09, 2012, 04:23 am Last Edit: Feb 09, 2012, 04:26 am by tnovak Reason: 1
Looking for criticism on this circuit, it takes 8 - 12v automotive input on/off signal and uses 2 opto-isolator PS2501-4A-ND to toggle 8 arduino input pins. The circuit shown is just for one of four channels of the PS2501-4A. It would be repeated 7 more times. Its a mix of other ideas I found on the web. Thanks


R2 is too large, it might not allow enough current to flow to turn the optoisolator on. I'd recommend 2.2k or 1k.

I don't think C1 is necessary.

R1 is unnecessary too if you enable the pull-up resistor on the Arduino input pin.

The Ruggeduino: compatible with Arduino UNO, 24V operation, all I/O's fused and protected


Feb 09, 2012, 04:55 am Last Edit: Feb 09, 2012, 04:58 am by tnovak Reason: 1
Thanks for the reply. I was confused about the resisters, I looked a another schematic that had R1 and R2 values switched, but I choose this way thinking it would provide better protection against spikes, also why I added the cap to absorb some of the spikes then the diode as last resort. But if it doesn't allow the opto to "turn on" I guess its to much protected. And if the others are not needed that only makes it easier. Not sure if the diode is the correct type either.  


Feb 09, 2012, 09:52 am Last Edit: Feb 10, 2012, 10:55 am by Grumpy_Mike Reason: 1
The diode is the right type.
If you want C2 for spike suppression I would make it smaller.
A 1K pull up on the arduino side is more robust than the 30K ish of the internal pull up.
Yes R2 is too big, look at the data sheet for the correct working LED current.


I have some 10uF and .1uF which one to you think would be better? Thanks


Use the 0.1uF as it will interfere less with the signal and will remove higher frequency noise.


I hooked the circut up on the breadboard with R1-10k and tried R2 with 1k, 4.7k and 10k ohm and all worked.
The voltage after R2 are as follows.

R2-10k was 1.07V
R2-4.7k was 1.110V
R2-1k was 1.145V

15.62V was the signal voltage.

Foward voltage rating for the opto is TYP 1.17V MAX 1.5V

Im guessing 4.7k would be the best value for R2 to cover swings in the signal from 11V-16V?? Any thoughts??


I want o do something very similar. What did you end using for your resistors and caps?

Did it all work OK?

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