Looking for guidance on how to select an LED / photodiode pair that would be used to detect whether two round non-metallic spheres are touching each other or not.
Hello vpschroeder,
Welcome to the DigiKey TechForum.
How do you plan to use these? Are you going to set them up and the spheres will come together and block the light between the LED and the Photodiode?
If you are still in the planning stage, maybe one of the engineers that monitor the TechForum, can help with this.
Hi vpschroeder,
We will probably need more information before being able to give any useful advice on this problem. Describing more about your overall system and its purpose might help guide a better response.
At a minimum, we would need to know the size of the spheres and the minimum required spacing between the sensing and receiving devices of your system. We would also need to know whether it must sense when there is an absolute contact vs. just “sufficiently close”, as the contact point of two minimally-compressible spheres is literally just a point, which means light just above and below the contact point will pass through to some degree. We would also need to now the ambient light conditions, as outdoor light makes the task much more difficult.
Larger diameter spheres will block more light vertically than smaller ones when the two spheres are in contact, making the task somewhat easier, but regardless, this is a very difficult task using optical methods, as some amount of light will always pass just above and below the contact point. Furthermore, if the potential contact point might not always be in the same 3-D position, then this greatly complicates aligning any sensors.
Randon thought, @vpschroeder,
Consider using a visible red laser and a photodetector.
The light spread will be less allowing you to aim at the beam at the center of the spheres.
Best wishes,
APDahlen
P.S. This is a challenging problem as the beam to sphere alignment is a critical adjustment.
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Spheres are approximately 2" in diameter with a typical ±0.005 inches (±0.127 mm) tolerance. Sensor would need to confirm the spheres are physically touching; aside from the aforementioned tolerances, assume the distances from center of sphere to reference plane is the same (Sphere midplane would be aligned with each other). I could likely control / limit the amount of ambient light if I need to, but would prefer not to, if possible.
Thanks for your suggestions so far - very helpful. Perhaps the above additional detail will help to rule out certain sensors vs others. Sounds like an LED/photodiode would likely not work..
Hello @vpschroeder,
Another random thought…
Use two lasers. Instead of pointing to the center of the balls, point to the edges. With your setup, the lasers would be slightly over 4 inches apart. Here we assume the balls are perpendicular to the laser detection gate.
Best wishes,
APDahlen
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