I know the ITADs and variations on a theme depends on breaking an infrared beam hitting a detector to trigger an action. The beam and detector can be pulsed to prevent false positives. Infrared from lamps and sunlight can cause problems.
Wonder how ultraviolet would work, though I would assume that ultraviolet from flourescents could also interfere just lke infrared?
Comments?
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The first thing that comes to mind is the potential damage UV light sources could do to your plastic trains. It may also be harmful to you, skin and eyes. IR is proven technology, why not just use it?
True consideration. However I am thinking small LEDs not high power stuff and small spread beam across track. Not sure if you could generate enough UV energy to do harm. But agin like the title says just for fun speculation.
I doubt that you could generate sufficient UV to damage anything, including eyeballs. OTOH, sunlight will certainly affect those sensors! In the old days of EPROM that you erased with UV light, a hobbyist's trick was to put them on a window sill in sunlight for a couple of days to erase them if you didn't have the UV eraser!
One advantage of IR is the availability of engineered-plastics that pass IR wavelengths while blocking others - such as the black lenses on IR remotes and sensors. Perhaps there are similar UV-tuned plastics but it seems materials are designed to specifically block rather than specifically pass UV for obvious reasons.
I think using pulsed light, and matching detectors tuned to this pulsing frequency (e.g., 40 kHz) has gone quite a ways to reducing false positives. I know some commercial ITADs use this method but many don't. Considering the added component cost to a manufacturer would be only $1 or so, and that ITADs go for $20-30 or more, perhaps a fun DIY project would be to upgrade a non-pulsed ITAD.
Since UV LEDs are readily available for well under $1, a DIY project might be a pulsed UV ITAD. It used to be that the IR receiver chips with the pulsed frequency detectors had the IR photodiode built-in so you were stuck with IR. Vishay introduced a pulsed frequency detector chip that allows you to add your own photodiode which doesn't have to be IR. Since the detection frequency is in the tens of kHz, it provides the 60 Hz line frequency rejection from conventional fluorescents. So provide a pulsed UV LED, the Vishay detector chip ($1), a UV-sensitive photodiode and lens and you're off to the races for a couple bucks.
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