Laser break beam sensor (ID: 2122)

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

Post by gordiegii »

Hi talking rock,

Here is the circuit I used.
talkingrock wrote: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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SensorDiagramLED.png
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gordiegii
 
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Re: Laser break beam sensor (ID: 2122)

Post by gordiegii »

This test circuit should show 5 volts when there is nothing in front of the sensor and zero when the beam is 'broken'.
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gordiegii
 
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Re: Laser break beam sensor (ID: 2122)

Post by gordiegii »

...and of course the microcontroller circuit:
SensorDiagramMicroCTRLr.png
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You could put an LED in series with the resistor here for external indication but the microcontroller input might not see a full '1' when the sensor is off. It should see a full '0' when the beam is broken though, with or without an LED.

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

Post by gordiegii »

And last, but not least, one that will give 0 volts when nothing in front of the sensor, full 3.3 volts and an indicator light when the beam is broken.
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talkingrock
 
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Re: Laser break beam sensor (ID: 2122)

Post by talkingrock »

Dear Gordiegii,

Thanks so much for your reply. I now have the break beam sensor up and running. While I am not schooled enough in light to understand your prior postings re polarized light options with this device, I have observed the following:

My project attempts to use the beam essentially to tell if something (that the beam is focused upon) has moved. This proved quite tricky. The target is about 2 - 3 feet away, and must respond in all potential lighting situations, from full sun to pitch dark.

I had assumed that I could make, say, a circular target (3 inches), with a reflective surface for the bullseye, surrounded by a light dispersive material. I found out that that did not work. In fact, the opposite has worked better than I ever expected. Namely, I have a little black rubber dot (3/4 inch dia.), surrounded by essentially a holographic surface (which was on the back of a 99 cent kid's compact mirror I picked up at the discount store). Pure eureka (at least for me) !! It works perfect. When the targeted object moves, the beam moves from the black rubber to the more reflective surface (the dot when hitting the holographic surface is way brighter), then unfailingly triggers the LED. I will need a latch down relay I am sure eventually, but this was the first test of the system.

Again, thank you so much. Feedback on surfaces is always welcome.

talkingrock

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

Post by gordiegii »

Glad to hear of your success.
Sadly, my attempts to realize the polarized system did not work. Diffusely reflective materials (eg. paper, felt, clothing, etc.) randomized the polarized light and rendered it visible to the sensor within the 1 to 2 m range. Beyond that range the retro-reflector worked as expected up to about 15 m with or without the polarizing filters. The only thing the polarizing filters did was allow the sensor to ignore mirror like surfaces.
If your target were 2 to 15 m away (6 to 50 feet) you could use a dot of retro-reflective tape as the bulls-eye and it wouldn't matter what was around it. Then you wouldn't need latching but if your distance is 2 to 3 feet then it sounds like you have found the best solution unless you intentionally attenuated the beam by passing it through some darkish plastic or glass filter.
talkingrock wrote:Dear Gordiegii,

Thanks so much for your reply. I now have the break beam sensor up and running. While I am not schooled enough in light to understand your prior postings re polarized light options with this device, I have observed the following:

My project attempts to use the beam essentially to tell if something (that the beam is focused upon) has moved. This proved quite tricky. The target is about 2 - 3 feet away, and must respond in all potential lighting situations, from full sun to pitch dark.

I had assumed that I could make, say, a circular target (3 inches), with a reflective surface for the bullseye, surrounded by a light dispersive material. I found out that that did not work. In fact, the opposite has worked better than I ever expected. Namely, I have a little black rubber dot (3/4 inch dia.), surrounded by essentially a holographic surface (which was on the back of a 99 cent kid's compact mirror I picked up at the discount store). Pure eureka (at least for me) !! It works perfect. When the targeted object moves, the beam moves from the black rubber to the more reflective surface (the dot when hitting the holographic surface is way brighter), then unfailingly triggers the LED. I will need a latch down relay I am sure eventually, but this was the first test of the system.

Again, thank you so much. Feedback on surfaces is always welcome.

talkingrock

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libero6
 
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Re: Laser break beam sensor (ID: 2122)

Post by libero6 »

sadamnissley wrote: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.
Hi sadamnissley,

Do you still have any of these sensors by chance? If so, would you be able to sell me a few? Looks like they are discontinued on Adafruit :( I'm looking for about 3 of them for a project I'm working on. Please let me know when you get the chance. Any help would be appreciated!

Thanks in advance!

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libero6
 
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Re: Laser break beam sensor (ID: 2122)

Post by libero6 »

Does anyone have any spares of this sensors by chance? If so, I'd like to buy some off of you! Looks like they are discontinued on Adafruit :( I'm looking for about 3 of them for a project I'm working on. Please let me know when you get the chance. Any help would be appreciated!

Thanks in advance!

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