As I understand it, photo beam sensors (and perhaps other emission types) work like this...

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it occurred to me, it would be great if there was a "scanning" such sensor...

enter image description here

So, it would rotate or swing, at many Hz, over perhaps 90 degrees. (It could rotate mechanically just like an airport radar or I guess a bar-code scanner, or perhaps "rotate" in some solid state manner.)

When an object cuts the beam, in fact it could tell you the angular bearing.

(Of course, if you put two or three of them over an opening, you could calculate a position in 2D nicely.)

In fact, does this technology exist .. is there such a photoelectric beam sensor -like device, which indeed will give you an "angular bearing"?

I've spent considerable time searching but not been able to discombobulate.

(I was astounded to learn there is a lidar-like thing that actually measures distance via time of flight, but that's sort of a further (amazing) complication, not really what I'm wondering about.) Thx, experts

PS I have no interest at all in model or manufacturer recommendations. I just want to know if such a thing exists. (For all I know, it's completely commonplace .. or it may be obviously "ridiculously impossible" to experts. Cheers)

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    \$\begingroup\$ Why does lidar not satisfy this? \$\endgroup\$ – Ignacio Vazquez-Abrams Jul 10 '15 at 12:56
  • \$\begingroup\$ You could certainly build one - by taking a standard lidar and adding a mirror on a stepper, or (at slower speeds) mounting it on a hobby servo. \$\endgroup\$ – Nick Johnson Jul 10 '15 at 13:08
  • \$\begingroup\$ Well, I'm feeling a bit discombobulated by this question if that's any help. \$\endgroup\$ – Jon Jul 10 '15 at 13:11
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    \$\begingroup\$ Is that like asking why a nuclear power plant doesn't satisfy the need for a 9V battery? :) I only want, or wonder if exists, a spinning 20 dollar photoelectric sensor, which would give the "angular bearing". Quite different from (incredibly) measuring distance with lidar at a very high price. \$\endgroup\$ – Fattie Jul 10 '15 at 15:13

The main obstacle to this is that a traditional beam break has a point source and a point sensor. The system as you described would have to have a linear sensor in order to tell you where the break was, which would be more expensive.

It's certainly not impossible. Related work includes "structured light" (combining a scanning or otherwise patterned laser with a camera to give a 3D image), or the Flat Frog system for very large touchscreens. That has a large number of LEDs and photodiodes around the edge and detects fingers by successively illuminating from different angles and looking for the shadow.

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  • \$\begingroup\$ Hi PJC .. hmm, you'd simply have a reflector on the "right" in the diagram. TBC we actually MADE! one, with two dollars worth of reflective tape, and I just rotated the sensor left and right with my hand (say every couple seconds). The flat frog tip is a fantastic one, thank you. \$\endgroup\$ – Fattie Jul 10 '15 at 15:10
  • \$\begingroup\$ So sorry I forgot to tick this .. someone should have messaged me! thanks again for the great answer! \$\endgroup\$ – Fattie Feb 14 '16 at 18:59

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