Interfacing Triacs with Logic Inputs
One easy way if load current is approximately 5 A or less is shown on figure below. The sensitive gate triac acts as a direct power switch controlled by TTL, HTL, CMOS, or integrated circuit operational amplifier. The triac can be activated by a timed pulse from the system’s logic from anywhere in the AC sinewave producing a phase-controlled load.
Correct grounding for DC and AC supply is the key to DC pulse control. DC ground and AC ground/neutral must be common plus MT1 must be connected to common ground as shown on figure below. MT1 of the triac is the feedback for both main terminal junctions as well as the gate junction. [Circuit’s schematic diagram source: littlefuse.com]