Hi Friends,
In one of my 8052 application I am controlling the current going to a heating coil with the help of two SCR's connected back to back. I have to keep the current going to the heating system at a desired value, even when the mains voltage drops. The mains voltage that we get here in developing countries like India is most of the times not consistent. I will be adjusting the firing angle of the thyristors to compensate for the drop in voltage so that the heating system always see a constant voltage. In order to determine the change in firing angle I need to measure the mains voltage. I am planning to use a ADC0809 to measure the input voltage. I will use a step down transformer 420V->6V then this voltage goes to an optocoupler for galvanic isolation the output of the optoisolator will be going to ADC. A 40MFD cap is connected to output of opto to minimize ripples. Due to the linearity of Opto [ MCT2E ] the output voltage from opto will be in relation to mains voltage. Thus the output voltage from opto will drop for any drop in mains voltage. I want comments or suggestions on this design. Also I want to know is there a better way of doing this.
Thank you very much.

Regards,
Prahlad Purohit