Actually, you have two options:
1. Connect DC power supply GND with Triac A1 terminal. Requires either an isolated supply or rearrangement of the AC load.
2. Use an optotriac for triggering
If you don't see the problem, study known operational example circuits and check, how they connected DC supply and AC circuit.
May I answer with counterquestion? How did you connect your DC supply with the AC power?
The connection isn't shown in your schematic. What's the return path for the current through R3?
In this case, the said solution of connecting triac A1 to DC GND can work. The AC load has to be connected between AC N and triac A2 instead (move up in the schematic).
purple line -> measure @ triac gate /gnd
yellow -> my mcu output to gate
blue -> voltage across the triac
it seems that half of ac have prbolem (blue line)
the positive half of ac was on (which should be off? that is when my mcu leg is low
there should be ac waveform
however the positive was missing that also imply the driver part still have probelm!??
hai Takbb, I had posted a triac driver in may old post. "&highlight=" The circuit is of a light chaser. But consider the MCU is used as an dimmer in your case. Triac driving circuit may help you. But i strongly think you need to use a separate regulated Power with 7805 for your MCU. and use the triac as in the link provided. Hope it helps.