I need to use a couple of transmission type opto interrupters to drive the coils of latching 12vdc relays. One opto interrupter will drive one relay coil and the other interrupter drives two relay coils. Each 12vdc relay coil requires 15mA of current to actuate. I am assuming that when the LED emitter beam is broken, the output of the interrupter's transistor will rise to allow the activation of the relay coil. Any suggestions for how to spec out the opto interrupters, assuming a 12vdc supply will be providing the voltage for the interrupters' LED and output transistor? Also, how do I size the dropping resistor for the interrupter's LED voltage and the output collector resistor? Perhaps there is already a simple schematic of this application. Thanks to you all!