I am using the ULN2803 (which has 8 Darlington pairs) for other functions (like driving relays) and since I had a spare Darlington left on it, I thought of using it to drive the triac.
I don’t care about isolation so this will work fine. Just need to know if the gate will sink high amounts of current into the OC output when it’s active (low) without a series resistor. If so, I will use the series resistor but that will add 220+500 ohms to +5V when the ULN2803 output is high — hopefully that won’t be insufficient current into the gate of the triac.
I am ready to cut traces and solder, so the above answer would greatly help me.