I'm butting in here, not to interfere with Mike - as I absolutely know he can and will respond if and when he feels like it- but because I have to agree with his post.
I would have never commented in this thread, had it not been for one sentence in your first post. Call me sensitive but I thought it rather arrogant of you to barf numbers all over the page, putting up the pretense of knowing what you were doing and then closing the post with:
I am leaving this post up in the hopes that the thought process involved will benefit someone else.
It could not be left to stand. It was totally wrong. Okay, you did ask for help. Fair enough. Then you got that help and you started to play the village idiot. Why? You had already demonstrated an understanding of the concepts, you just had all of the data points wrong.
Then it's Explain it to me like I'm five? Seriously?
Please stop with the wounded routine when you get exactly what you give. It's the Internet. I'd actually say everybody has treated you pretty darn well, considering the fact that it was us that had to teach you something. At times, it almost seemed as though you didn't want to learn. Suck it up and move on.
What is missing in all this R2 value stuff? The optocoupler transfer ratio. You/We have absolutely no idea what it is. It's worst case 50%. But what happens with no resistor if it's best case of 300%? What then?
Holly two cent resistor Batman. Use one or not and please move on to something more beneficial. To everyone. Enough already.