Breaking a light beam as a form of sensor (home for the blind)

[zenerbjt]

Dear Engineers,
Years ago I worked on a sensor system for blind and partially sighted people (in a huge home for the blind) whereby we had light beams going across the corridor, and whenever someone walked past it would tell them where they were in the huge building. (they would be walking whilst holding on to the rails on the wall) I cant remember what sort of sensors and LEDs we used for this. Do you think it is likely we would have used infra-rad? I mainly worked on the power supplies so cant remember the details of the “light beam break” sensors.

Can you possibly help with a suitable sensor/LED system for this?

 

[betwixt]

Almost certainly infra-red and with lenses on the emitter and sensor to narrow the beam width. Most systems like that use a modulated beam, usually chopped current at a few KHz to make it easier to distinguish from background light sources and other IR equipment.

Brian.

 

[wwfeldman]

it was done (long ago) with visible light
(since there weren't any LEDs etc)

this might meet your requirements (a good price)

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there are many (relatively expensive)

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[dick_freebird]

There are now many, many cheap, cheap
pyroelectric motion detectors whose back
end could easily be altered to switch on an
annunciator instead of a light or LED-bank.

Makes it a single-point install instead of a
two-point plus alignment deal.

Tons of "organ donors" on eBay and amazon....

 

[zenerbjt]

Thanks ill look into motion sensors.
But for now i wonder why IR is used.....is it because its low frequency and so less attenuated by air?...or just that its sensors are cheaper.

 

[wwfeldman]

i think most of this sort of technology grew out of security systems
since you can't see it, you won't try to avoid it, and you've been caught