Input Filter for Digital Dimmer Circuit

I have a digital dimmer circuit that controls the voltage to a lighting load through phase cut technique as per the attached image. I am using a micro controller that receives the zero crossing signal and send the firing signal to the circuit to control phase cutting. The circuit is working fine in most conditions. It has only one drawbacks is that when another load that is being fed by the same power supply is switched on or off or causing noise to the power supply the dimmed lighting load flickers momentary or for a short period then again stabilized. I need an expert to modify the circuit in such a way to isolate or filter the input voltage to the zero-crossing circuit to avoid any fluctuations or flickering being affected by any near by load. The original circuit is attached here. I need only a practical schematic for the updated circuit with parts list being added. The new circuit is required to be as much simpler and economic as possible. Payment will be released only after ordering the required parts list and testing the suggested schematic to make sure it will work.