/diy/ - Do It Yourself

Might as well post this here instead of making a new thread.

I'm new to electronics and I've got a project I'm currently working on that involves sensors. I'm using a diode/transistor setup for this but I'm having trouble calculating appropriate resistor values to use.

According to the datasheet (which I'll post as a reply to this) the maximum ratings for the diode are 2V and 40mA. If I was to use Ohms law to figure out the resistance required to get these values across the diode would I be able to just use R = 2 / 0.04? I'm not sure which value to use for V when I have the input voltage as 5V and the desired voltage as 2V.

The current resistor values in pic related are just placeholders.