Convex LED Lens?

[Electric Rain]

Hi, does anyone know where I could get small, cheap, plastic lenses that I could use to focus an IR beam? Example: The ones used in IR beam breakage detectors. It doesn't need to travel far; no more than a foot. The diameter of the beam should be no larger than 3mm; the diameter of the infrared emitter. Thanks.

P.S. Could I just put the emitter in a tube to focus the beam to 3mm, or will it still spread once it leaves the tube?

 

[dknguyen]

Diffratction

It will spread due to diffraction. (Think about how a flashlight doesnt turn into a laser if you put a carboard tube in front of it.

 

[Electric Rain]

It will spread due to diffraction. (Think about how a flashlight doesnt turn into a laser if you put a carboard tube in front of it.

Ah yes, this is true... alright, then where do you think could I get those lenses?

 

[dknguyen]

DKNguyen

Have you chosen your IR source yet? I'm pretty sure it's highly dependent on that. Have you tried looking for an IR diode with a lense? Lenses are already pretty hard to align already, and on something 3mm, I am not sure how you would mount it unless it was built for that particular emitter.

For example:
**broken link removed**

That particular actually has a beam-width deviation of 0.7 degrees from the center (3in diameter spot at 10 feet). The one in the article is the CLE333 and has the smallest beam angle. There are others available but the only other one that has an angle small enough for your application is the CLE331 (beam angle is 5degrees from center). If you want to pursue these then you can go to:

https://www.clairex.com/ and look under
Products>Point Source Emitters

to look at the spec sheets. Regardless of the emitter, you do not want labelled flat window for the lens because the beam width will be too wide for you. The spec sheets should have more info. They have an online ordering website where you can get it for about $5 (+$15 shipping so stock up!).

Another good way to go would be just to get a laser pointer, but if you want IR, then IR lasers are class 3b no matter what how weak they are (because you won't react to the laser if it shines into your eye). VIsible light would work fine since you can't see a laser beam mid-air unless there was smoke or fog or some other airborn contaminant to reflect off enough light back to your eye. Plus you get that cool Mission Impossible effect when you cross the beam. But if you plan on modulating, using a laser pointer might be a bit harder to do.

I personally was pretty impressed with the CLE333 specs and price and am trying to think of a way to use them on my robot.

 

[dknguyen]

You ran out of room in your PM folder for "Consolidated Response 3", so here it is:
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CONSOLIDATED RESPONSE 3
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Also, note that you can get false positives by stepping on non-button positions that activate the same rows and columns as an actual button positions. The MCU will think that the non-valid positions are not actually happening (because no buttons are there) and pair up the columns and rows in such a way as to make them correspond to valid buttons (which you are not actually stepping on).

To solve the problem of the above two paragraphs, I think you should get a thicker board and drill large holes into it and place photo receivers in there. Then you can use the light/darkness of the photo receivers to reinforce the beams. This requires some light in the room that you are playing however, and you need to get photo receivers that respond fast (photo-diodes).

You can actually use this photo method to reinforce the beam method (you only need a photo-receiver in the valid positions).
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The part that makes all previous parts irrelevent
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But if I were you, I would scrap the whole beam method altogether and instead just use the photo-receivers. Less processing involved, more durable (can't side swipe the beam sensors) and you can make an individual sensor for each pad with less parts than making a "ring of beam sensors" around each arrow. 4 photo-diodes as opposed to 32 beams each of which is much more expensive than a photo-diode. The only requirement is you need a certain amount of light in the room and the sensor MAY activate before your foot actually reaches the ground depending on the dark/light threshold you have set it to.

To read about sensitivity and speed of photo-transitors and photo-diodes, go here (there is a tradeoff between speed and sensitivity, but too much sensitivity isn't needed for your application).
https://en.wikipedia.org/wiki/Phototransistor

Stupid 5000 character limit.