help me to use my 4 pin optocoupler

Please, I am having this challenges using my 4 pin opto coupler I need the best and reliable design on how to bias my c945 transistor from pin 3 and 4 in order to operate 12v relay on 12 v battery. I
cant read the number printed on the opto coupler I need a general approach.

thanks

hi,
What is the opto coupler type.?

I cant read the number but a 4 pin opto coupler
thanks

This is first picture that I found...https://jaenal91.files.wordpress.com/2009/02/bb.jpg

Put your multimeter on diode test, then check between all pins until you find a diode junction of about 1.2v. That is the LED.

Connect 5v to the LED through a 1k resistor, and check again that the LED is fixed at about 1.2v.

The remaining 2 pins are the opto device. Connect 5v through a 47k resistor to one pin, the other pin to ground. If you have these pins the right way around one pin will read 0v, the other about 0.5v or so.

When you disconnect the power to the LED pin the 0.5v pin will change from 0.5v to 5v.