http://www.scribd.com/share/upload/10788385/12mvfg4erw04i2xouv8l


please help me know the use of triac and opto-coupler in this circuit.
the opto coupler is used for switching purposes with isolation,then why is theere no ground in the astable mode operated multivibrator(555 ic) .
please give a overview of how this circuit works!!!!!

 

There is ground.

Why you say that?

 

The circuit is bad news as it uses the line for power. If you use a 12 volt wall transformer to power the 555, it will function the same way, and be safe to use.