Hi everybody,

I have got the zero detection pulses when I used phase instead of neutral between the two diodes ( any explainations why? ) but pulses were not square as I desired (may be the port input takes some time to sink the +ve voltage) Then I tried opamp 324 as comparator with 2.5v as reference at non-inverting input and pulses detected earlier at inverting input I pulled up the output using 4k7 resistor.
I am getting the square pulses.
If you can help please send a routine in assembly to calculate the pulse width of these pulses. I got the triac working with Kunal's suggestion and am getting variable speeds of the motor.
As you know I am trying to control the firing angle of triac according to input pulses by the rotary sensor.
As load is applied on the rotor these pulse width would widen.
Your suggestions will be useful.

Regards,

Nitin