If you're looking at this thing, be aware that this mod will require a light hardware mod, potential soldering, and a firmware tweak. Must be running Marlin Firmware!
I got mine from Aliexpress, but you can get them anywhere really.
Optical Pros & Cons:
This optical endstop uses an optocoupler, which serves as a non-contact endstop. This means that there is no concern for mechanical wear, as there is with limit switches. Another benefit is that the noise is reduced as you don't hear that thud or clicking noise when the axis reaches the endstop.
The technology of course is not without flaws. It suffers from the same conditions that a BJT will suffer from. Variance in temperature and humidity will affect the repeatability; however, it is not impactful, and we are not seeking micron accuracy as we do on the Z axis because we just want to roughly know the edge of our bed.
Before installing the print, I modified my left idler with a dremel and a rasp. I removed the limit switch mounting and part of the motor mount in order to access the set screws on the coupler without completely removing the motor. If you decide to try this setup, you might get away with that limit switch mounting still on, but you're zero point may be somewhere on the bed itself depending on the footprint of your extruder carriage.
This next part isn't necessary. I didn't want to use the female dupont connectors in the male JST-XH-03 from the Anet's control board. I flipped the cable, cut off the dupont side, and directly soldered the wires onto the Optical Sensor. This allowed me to match the JST connectors. I had to swap the signal and 5V wires on the JST connector to finish the job.
Wire routing will be up to you. I ran mine down and zip tied them to the motor's wires.
Just as I mentioned earlier, Marlin Firmware is necessary. You need to go into the settings and invert the logic in the configuration_adv.h file. The sensor outputs high until the flag triggers it. Then it goes low. After this, you should be set.
If you got this far and you're looking into trying this, then you more than likely have some basic ability to create CAD models. I provide a basic Flag to trigger the sensor. In my case, I glued the flag onto my carriage. You could either do that or create your own custom flag.
I almost hope nobody tried this as it's very tailored to my setup. I'd rather you ideas or some starting point so you could come up with something better. Optical Endstops are the way to go.