opto-coupler ON/OFF threshold levels
Yes, you can do something like put a couple series 6.2V zener diodes and a 6.8K resistor. Also put a 10K resistor across the opto input. 







simulate this circuit &ndash; Schematic created using CircuitLab

The current will not be very high, so R3 has to be pretty high considering the low CTR of this part. Maybe ~20-30K.