Currently I am looking for a (preferably rather compact circuit) that will test whether a certain signal has been on for X amount of seconds.
Just get a Pulse Length Detector, you might say. Only there's a problem with that. When the input signal gets turned off and then back on, the old 'test' will still be successful and a signal will be emitted.
Is it possible to somehow make a 'perfect' test for an uninterrupted redstone signal of X seconds that does not get confused by several shorter pulses?