Dear Erik,

The application just running well if no one put something (solder, rice cooker, etc.) to the public ac power line in the same house, or if no appliences
like solder, fan, etc is pulled out from the power line.

But whenever the appliences is pulled out or put in,
the application will do something like there a sensor
just been triggred.

The AT89c51 is a slave for another application.
The power supply just the 220v public main ac supply.
In addition to IR, the AT89C51 controlling a stepper
motor.

Thank you.