This must be school project. There is due date, is it?
Here is my best shoot;-
1. Replace T1 with SCR+full bridge rectifier ( I did SCR+full bridge rectifier to replace triac when I was kid, since triac is much expensive than SCR+full bridge rectifier that time)
2. Make all the related parts meet your AC voltage.( they might design for 110V, if yours is 220V)http://playground.arduino.cc/Main/ACPhaseControl
copy and paste Arduino code above, modification might need if you design 50hz instead 60hz.
last thing is document
copy and paste every thing from above again, if you need more content I put a little more here for copy.
1. The SCR will be triggered by a very fast current pulse. make sure capacitance of the opto triac is not able to generate such a pulse under a high dv/dt transient.
2. Select opto triacs have good dv/dt rating to increase effective dv/dt of your power circuit.
3. Make sure voltage rating of the opto triacs has enough margin, 400V for 110V AC, 600V for 220V AC.
4. The LED suffer from gradual degradation and no exception for opto triacs here. the driving current margin is needed, compensated degradation.
5. Protect the SCR gate against unneeded negative gate current. In this circuit no need do anything since full bridge rectifier force everything positive.
good luck and have a fun with copy and paste!DISCLAIMER:
Author here is sharing more than quarter century old knowledge!
High voltage is dangerous! Be careful.
No responsible for any damage or harm.
Don’t try follow this unless you absolutely know what you are doing!