Thank you Martyn - I think essentially what I want to do is to be able to export only the log immediately after a transition occurs. I'm reasonably sure the rise and fall time on the square wave is very much less thank a millisecond so only very rarely would the log fall during this brief interval. ...

Dear All I would appreciate you help on the following: :( I have a screen flickering between a black and white image at a rate of 1 Hz i.e 2 reversals per second. However, I need to know how stable this flicker is down to the millisecond (preferably 1ms) I set up a photodiode light sensor which is s...