Thank you for the Triac topic. May I suggest the following: 1) Label the graphics with the MT1 and MT2 sides of the Triac. Bold / Red that the graphic that does not work. 2) Point out that a Triac controlled by a Diac is also available as a single package and is known as a Quadrac. 3) When I came looking for this topic, I was looking for a page that told me the differences between a Triac and a Quadrac when trying to control them. For example, can I control the Triac with a transistor from a MCU (I think the answer is No). Can I control the Quadrac with a transistor? 4) I am trying to control a 120V 15A heater using a Triac / Quadrac and an MCU controller. My list is narrowed down to MOC3023 (Opto Triac Driver) and MOC8021 (Opto Darlington). I think I can use them in the following combination: -- MCU -> MOC3023 -> Triac -> Heater or -- MCU -> MOC8021 -> Quadrac -> Heater Thus, I am not expecting an answer here, just telling you why I came asking the Triac / Quadrac question. Thank you for the great site.