Trigger laser (or break a beam) without anything on the other side

Is it possible to detect when a laser beam is broken without a photocell (or similar device) on the receiving end?

I'm not particularly married to a laser but I'm interested in the concept of "breaking a beam". The only restriction is that the circuit behind it (in this case an Arduino UNO/MEGA) needs to be able to tell that the beam was broken in under a millisecond, otherwise the solution is not useful in this case. I've tried this with infrared proximity sensors and it works but it's a couple of ms too slow (at least with the ones that I had lying around). I also tried a PIR sensor and the lag time on those is over a couple of seconds, so it's not good either. Photocells seemed to work best for this but in my application I can't place them -or anything else- on the receiving end; it has to be a one-sided operation only, so to speak.

Any recommendations will be greatly appreciated.

Is that supposed to be a serious question ? Is it possible to call someone who doesn't have a phone? How would you respond to that question ? Is there any difference? You have a transmitter (laser) but no receiver. How do you suppose you wiuld detect if the beam was broken if you have no way to define " not broken" ? Are you going to reply " oh, that's simple. It's not broken if the beam doesn't hit anything !" ? How would you know that?

What kind of the trespassing object, size, reflectivity in optic & RF, magnetic property,

Is that a question? What difference does it make? How is that important?

Is that supposed to be a serious question ?

raschemmel, thanks for your prompt reply. It's very informative and helpful. I'm sorry we're all not as smart as you and if I had known that this question was too stupid to be even considered a serious question I would not have offended you by posting it. But hey, you can now consider yourself a well fed troll.

Magician, the objects will trespass at different speeds, free-falling mostly but I can't guarantee the same speed. They will be small (think 1-2 cubic centimeters) and always opaque and solid. Shapes will be irregular and materials vary from wood, to metal, to actual food (candy). I need to react quickly because I will need to photograph them and push them away with a solenoid-like device. In some ways what I'm trying to achieve is very similar to this kickstarter project ( except that in their case you point the laser to their gadget and they handle the rest.

Since I posted this I got a few suggestions that I still have to try but I'm open to other ideas. What was suggested to me was to do this visually with a high speed camera rig that someone offered to lend me (think massive 125000 frames per second), and also tap into the depth information of a Kinect. The first one will be fun to test but incredibly expensive since I don't own the rig and to achieve those speeds you need way too more light than I can install in the installation, but the second one I can do without a problem as I've coded a few things for Kinect before so I know the API.

Use a mirror on the other side and reflect it back.

steinie44: Use a mirror on the other side and reflect it back.

Actually, it's not a mirror as such, but a "corner reflector". The things you see on the side of the road which reflect your headlight at night. They come in red or white.

Hmmm I like it. While I cannot put anything "electronic" looking on the other side, I think I can get away with a small reflector like these. I just ordered one to see what kind of mileage I get from bouncing a laser off it. Thanks for the suggestion!

They have one of those reflectors on the moon . Is that enough mileage for you ?

Not that it matters now but how do you think a military laser range finder works ? You didn't ask if you could use a laser to measure distance or I would have mentioned this. You also didn't ask if you could detect the reflection of a laser beam from the source. Hindsight is always 20/20. Calling people Trolls is an unprofessional response and any name calling for that matter is a sign of immaturity. If you were offended by my response you certainly have the right to say so but I think resorting to name calling is a bit childish.

yes this is posible :roll_eyes: think about laser measurement ,, it works like this ,, when you pint a laser ,, the dot wil be bigger and smaller depent on how far you shine ,, when the dot increase the cm increase ,, ,, i use some kind of system on my quadcopter for some project ,, not a strange question ,, but strange answers ,, ;) you can build a system ,, using a laser a LDR and a lense ,, for on the ldr ,, then make a smal box and hole like a needle behind the hole the lens comes , and behind the lens the ldr ,, now the ldr and the lens and the little hole act as a eye ,, now it needs to see the laser ,, true the eye hole , do you gett it ,, lol butt this is one way to make cheap one ,, ;) in labs whe use laser to measure dust in the air ,, a particle ,, whe test the sterile conditions ,, and check air for contaimends ,, so yes it is posible

And of course there's also Passive Infra Red which doesn't need a receiver on the far side or a reflector over there and a receiver over here. Might be worth a look, at least.....

thinking about this,,,, a room motion sensor does not require something on the other side, but the object itself is the 'other side'

radar works in a similar way, send a signal out and listen for the echo

laser range finders run in the 1 to 10 hz range.

it appears that the answer to the subject line is a simple no, cannot be done. whatever 'breaks the beam is 'the other side' the actual project seems to be, can I measure a falling object with a sensor. the answer to that is yes, multiple technologies.

next question is can it report an object within milliseconds.

how far away is the object ? greater distance, longer response time, even at the speed of light. speed of the object is based on simple calculations. distance from the release point to the plane of the sensor. the maximum speed was revealed by Newton. the object will fall at 32 fps ps until it reaches terminal velocity for the object. terminal velocity will have both resistance and air density. a feather has high resistance, a vacuum has no density. 1,000,000 times zero yields the same result a 1 times zero.

a single sensor above the focal point with the expectation that by the time the sensing and calculations are done, the object will have fallen x mm more would require setting a value for the resistance (assuming standard air density = 70°F, 50% rh, 29.92 in hg) distance is key as well.

so, the question really being 'how can I detect at high speed, a falling object "

I would look towards what a projection line does for sugar or nuts. as the product falls over a sensor, the sensor looks at the object, determines if it is correct, then uses a puff of air to blow nonconforming parts out of the main steam.

may I offer that it is easier for us to help you when we have a goal. just asking if one type of sensor can do one thing will immediately exclude all the depth of knowledge of the community.

quite simply, the only possible answer to your question is no. it is not possible. the object breaking the beam is the other side, therefor your question is faulty.

reading the responses, the community has pretty much ignored the wording of your question. partly because we do not like 'no' as an answer and partly because you have altered it with with more information. And the community has chosen to offer solutions to the actual un-asked question.