birdhouse:
Hi Tom and Aarg,The SCR works! Thank goodness, It must have been what you suggested, about the opto triac limiting the current.
Great that you have it working. However, many people including myself have used the opto triac with absolutely no problems. Your diagram is labeled 5V but the Due is a 3.3V board. Maybe the Due requires different resistor values to drive the opto triac properly.