Laser break beam sensor (ID: 2122)

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gordiegii
 
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Laser break beam sensor (ID: 2122)

Post by gordiegii »

A bit of nit-picking here but this isn't really a beam break sensor, is it? It's really a diffuse reflective proximity sensor.
It could however be turned into an amazing beam break sensor with a reflector and a couple polarizing filters.
I haven't got one yet (they're out of stock) but I suspect they could detect a retro-reflector a lot farther than one meter away. The cool thing about corner reflectors (the thickish plastic ones with the little cube corners inside, usually seen on cars and bicycles) is that when they reflect polarized light, they rotate the polarization 90 degrees. Now if you put a polarizing filter in front of the laser (if you actually do this rotate it until you get the brightest beam, LED lasers tend to put out light that is somewhat polarized to begin with) and another one rotated 90 degrees in front of the sensor, then the sensor will only be able to see the reflected beam if it was reflected by a corner reflector. Light reflected by normal objects will be nearly invisible to the sensor, even within the one meter range. So if you shine the laser on a corner reflector on the other side of the room, for example, it should turn the sensor on. Then if somebody walks through the beam, even in a bright white suit right in front of the sensor, the sensor will turn off because it can't see the beam reflected by the corner reflector.
That would be a laser beam break sensor.

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adafruit_support_bill
 
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Re: Laser break beam sensor (ID: 2122)

Post by adafruit_support_bill »

It's really a diffuse reflective proximity sensor.
Thanks for the feedback. I don't have one of these either yet (they sold out almost instantaneously!) But from the photos, I suspect that is a more accurate description. I will forward this to info to our web/catalog team.

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sadamnissley
 
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Re: Laser break beam sensor (ID: 2122)

Post by sadamnissley »

Has anyone had some experience with product 2122, Laser Break Beam Sensor?

I bought one, wired it up, and used it successfully.

After about an hour, the beam dimmed significantly, and it no longer reads. Any input would be much appreciated.

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adafruit2
 
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Re: Laser break beam sensor (ID: 2122)

Post by adafruit2 »

that's odd, what voltage did you feed it?

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sadamnissley
 
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Re: Laser break beam sensor (ID: 2122)

Post by sadamnissley »

I used 5v from Raspberry Pi.

Red wire - 5v
Black wire - Ground
Blue Wire - going to pullup resistor across 3v3 and an input pin.

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adafruit2
 
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Re: Laser break beam sensor (ID: 2122)

Post by adafruit2 »

well, lets try replacing it - email support@adafruit for a new one! :)

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gordiegii
 
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Re: Laser break beam sensor (ID: 2122)

Post by gordiegii »

I finally got one. (not delayed by Adafruit. Just got around to ordering it.)
adafruit_support_bill wrote:
It's really a diffuse reflective proximity sensor.
Thanks for the feedback. I don't have one of these either yet (they sold out almost instantaneously!) But from the photos, I suspect that is a more accurate description. I will forward this to info to our web/catalog team.
Somewhat odd what affects the range.
Yellow pine drawer front: 1 to 2.5 meters (left side of drawer vs right. I can't see any difference but the sensor seems to care)
Concrete: 0.7 m
Eggshell white painted wall: 1.5 m
Retro-reflective tape: at least 10 m (length of my appartment. will update)

I haven't touched the sensitivity adjustment yet.
I am looking for a dead pair of polarized sunglasses and a corner reflector. I will update once I find them.

Ontario license plate (indoors, 5 degrees off axis): 15.5 m
Last edited by gordiegii on Sat Nov 15, 2014 4:24 pm, edited 1 time in total.

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adafruit2
 
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Re: Laser break beam sensor (ID: 2122)

Post by adafruit2 »

Flat & shiny = good!
rough & diffuse = bad!

:D

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sadamnissley
 
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Re: Laser break beam sensor (ID: 2122)

Post by sadamnissley »

So I have confirmed that over time (the amount of time seems to vary by unit) the laser intensity, and overall sensing ability changes significantly.

Example: Set up a sensor to detect the presence of a paper product that was light brown in color. After less than a week, the sensor would no longer detect identical products at the same distance, but when presented with a product that was white in color it functioned normally.

I have tested this with several units (I have about 15 of these sensors, identical), and a variety of products for detection.

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adafruit2
 
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Re: Laser break beam sensor (ID: 2122)

Post by adafruit2 »

OK thanks for the note. we're going to pull these and ask. We did a bunch of testing but not for over a week :/

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MathInAction
 
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Re: Laser break beam sensor (ID: 2122)

Post by MathInAction »

Hi sadamnissley,

I am new to electronics, but I think that the description stated that the voltage across the input had to be 5V or the device wouldn't work properly. If you run a pull-up resistor to 3.3V could that be the problem?

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adafruit2
 
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Re: Laser break beam sensor (ID: 2122)

Post by adafruit2 »

the power supply has to be +5V, the pullup resistor can be to 3.3V

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sadamnissley
 
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Re: Laser break beam sensor (ID: 2122)

Post by sadamnissley »

Hello MathInAction,

So you would connect the red wire to 5v, and the black wire to Ground. The blue wire goes to an input pin. You also connect a pullup resistor from 3v3 to the same input pin.

So this uses reverse logic in your programming. When the laser beam is "unbroken" the input pin will read High/True/On because it is being pulled high by the resistor to 3v3. When something "breaks" the laser beam, the blue wire will offer a better path to ground than the input pin, and the pin will read Low/False/Off.

If you want more help, just write up the details of your project and I'm sure we can point you in the right direction with wiring diagrams and/or code examples.

Good Luck!

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talkingrock
 
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Re: Laser break beam sensor (ID: 2122)

Post by talkingrock »

Help,

I'm a novice trying to test my laser break beam sensor. I can't get it to respond to a beam breakage, notwithstanding messing with the sensitivity pod. I have the enclosed resister (I think) pulling up to the same voltage that I am using for the positive lead (e.g., 5 volts). When I break the beam however, my meter does not detect the output (blue wire) going to ground as I thought it would. It is basically the pulling up output voltage, depending on which side of the resistor I test.

Please help. Does anybody have a pdf schematic of this test circuit, preferably with an LED sub-circuit for testing beam breakage?

Thank you.

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talkingrock
 
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Re: Laser break beam sensor (ID: 2122)

Post by talkingrock »

[quote="sadamnissley"]

Help,

I'm a novice trying to test my laser break beam sensor. I can't get it to respond to a beam breakage, notwithstanding messing with the sensitivity pod. I have the enclosed resister (I think) pulling up to the same voltage that I am using for the positive lead (e.g., 5 volts). When I break the beam however, my meter does not detect the output (blue wire) going to ground as I thought it would. It is basically the pulling up output voltage, depending on which side of the resistor I test.

Please help. Can you please share a schematic of this your circuit, preferably with an LED sub-circuit for testing beam breakage?

Thank you.

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