Even photosensors have a tendency to produce more than one transition for each interruption. Unless designed not to, they can respond to the changing reflection from fingerprint skin variations as your finger is brought near the switching point. Similarly with a mechanical shutter, particularly if there are multiple ambient light sources and especially if they are ac-driven..
Such things are never quitre as easy as they first might appear..
-- Sue
I was just being flippant about the "delay" issue that the OP seemed too worried about.
- Tom
-
- Also snipped a couple of OT NGs. Don't re-invent the wheel. See
-- Roosters crow at the dawn, hoping to arouse the barnyard, but the owl knows it is still late at night. The foxes are about; the master sleeps. This is who we are.
ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.