How to correctly simulate Zero Cross Detector Circuit?
I have tested this that and found that there are something unstable over it. It develops a form of "noise" which disturb the signal. This takes place between every 30 seconds to 1 minute. (Perhaps my setup?)

This is a simple one



Opdate:

About the message "Simulation is not running in real time" here, try the following.

Select 'Set Animation Option' from the menu system and simply push the 'SPICE Options button'. Try to put [ABSTOL] down to, for example 1e-08 and see if it helped.

If it has not helped, try to go further down or if it helped, try to go one up by one until the error recurs, then go one down.