Basic design operates on 230V AC line. For 115V use R1 180 Ohms. Triac used in design (STM T435-600B) has continuous current 4A. To work with 8A you can replace it with STM T835-600B. Both are same package (DPAK). Traces are design to higher current. If you want use more sensitive triac (less than 15mA) change C1 to 0,1uF and R2 to 2400 Ohm. Control is designed to accept 3.3V. For use with different voltage change size of resistor R3 (minimum input to MOC3023 is 5mA - recommended little more).