The software I've used to do large samples is Cool Edit. I think you can download a sample version. Whilst it is not an oscilloscope package as such, it does large samples and you can cut, magnify etc. Use google to search for 'cool edit pro'.

As for the flickering - you need to confirm that your code is properly synched to the mains zero crossing otherwise anything else is a waste of time. Once this is confirmed, you can then start looking at other possibilities.

Don't write off your analog oscilloscope - with a little bit of thought you can do most things with it. The trick is trigerring it at the right time - by adding in diagnostic code to toggle a port pin to trigger the scope at critical times allows you to look at the item of interest. With the 8051, a port pin toggle is only 1 instruction so it has minimal impact on the rest of the code. This is a very powerful debugging technique. I've been able to survive without a DSO for many years now - I only have my trusty Tektronix 2465 analog scope.


Can you rule out that the flickering is not caused by an insufficient load? Thyristors have a minimum hold current, go below this and they WILL flicker.