3mm vs 5mm IR break beam sensor

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joehuber
 
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3mm vs 5mm IR break beam sensor

Post by joehuber »

I want to detect a pretty narrow object as it breaks the IR beam and so I'd like to know if the 3mm or 5mm version would be best at detecting small objects? The distance between the sender and receiver would be around 1 inch, and the only spec difference I see between the two is the 3mm is rated for 10" and the 5mm is rated for 20".

Does the 3mm possibly have a smaller sensing area and thus be easier for small objects to block?
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millercommamatt
 
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Re: 3mm vs 5mm IR break beam sensor

Post by millercommamatt »

You can shroud the sensors to narrow the field of view.

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joehuber
 
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Re: 3mm vs 5mm IR break beam sensor

Post by joehuber »

Thanks... we've been discussing including a pinhole or a maybe a circular tunnel ie like a soda straw to narrow the view. But we don't want to unnecessarily limit the aperture and affect the sensitivity.

I guess we're just trying to understand any differences between the 3mm and 5mm versions and use the most effective one when the sensor separation distance isn't a factor.

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adafruit_support_carter
 
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Re: 3mm vs 5mm IR break beam sensor

Post by adafruit_support_carter »

Either one of these would probably work. Heuristically, I'd go with the 3mm / 10" sense range version since it's closer in spec to what you are doing. And then the idea of adding shrouds to limit sense area is something you could play with. They both have an LED angle of 10deg. You can think of that as a 10deg cone to give you some idea of the sense area.

Too bad these don't have a better datasheet :(

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joehuber
 
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Re: 3mm vs 5mm IR break beam sensor

Post by joehuber »

Thanks for the info. I received the IR Break Sensor today and started experimenting with them at 1" separation and discovered it's pretty hard to block the beam unless I obscure it right at the sender. I think the output power is so strong that even indirect reflections get to the receiver and keep it activated. So I'm going to try adding shrouds with pin holes, reducing the Tx to Rx separation to about 0.25" and also lowering the voltage to the sender to reduce its output levels.

I need to achieve very fast response time to a small and fast moving object so I guess I need to get the beam power just above the receive threshold so that a modest obscuration is quickly sensed as a blocked beam.

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adafruit_support_carter
 
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Re: 3mm vs 5mm IR break beam sensor

Post by adafruit_support_carter »

FWIW - checkout this project:
https://learn.adafruit.com/toy-car-speed-timer/overview

It's also using the break beams at fairly close distance.

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adafruit_support_bill
 
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Re: 3mm vs 5mm IR break beam sensor

Post by adafruit_support_bill »

How small an object are you trying to detect? If the diameter of the emitter is larger than the cross-section of the object, it will not be completely obscured. A shroud and/or pin-hole aperture on the transmitter side will avoid that problem. A shroud on the receive side will help block out any interference from ambient IR sources or reflections.

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millercommamatt
 
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Re: 3mm vs 5mm IR break beam sensor

Post by millercommamatt »

My lab has an instrument that detects falling objects using ir beam sensors; snowflakes in our particular application. Using standard 5mm IR LEDs with some clever shrouds, the instruments can detect falling objects the size of a grain of table salt. The instruments software monitors changes in the voltage out from the receiver. I don't have the details. But, it's working proof that this kind of hardware is able to do what you're looking for.

Now the Adafruit model has a transistor in there. This means the output is digital and I suspect that you can't really control when the receiver goes high or low. This means that you could potentially shroud the sensor too much and it won't go high and/or a too small object may not cause the sensor to go low. Only trial and error will tell.

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armpm
 
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Re: 3mm vs 5mm IR break beam sensor

Post by armpm »

Purchased 6 IR Break Beam Sensors; item # 2167. Only one works satisfactorily, one barely and four no response detected. Would like to return for replacement that works or refund.

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Re: 3mm vs 5mm IR break beam sensor

Post by adafruit_support_carter »

@armpm Please start a new thread for your issue.

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