I have been testing using the Clear resin to print a case for a PIR motion sensor, but have found that IR light does not seem to be able to penetrate the clear resin. I have tried an unpolished clear case and a polished clear lens (not polished well enough for a camera but works as a magnifying glass). Both of my tests have involved curing from natural sunlight.
I would have expected that the clear resin would be IR transparent since it is heavily marketed as being optically transparent and since acrylic is often used for encasing PIR sensors. Does anybody have experience with printing covers for PIR sensors or IR transmitters? Is there a step I’m missing perhaps, or is this simply impossible?
most infrared motion sensors i’ve seen use a semi opaque white cover that is super thin.
also- how thick are you making the lens?
I suspect that the white formlabs resin is just the clear with a pigment… but have you tried a 0.5mm thick Durable resin? most IR sensors have a red tinted translucent lens… partly to filter out much of the visible light spectrum.
I was so focused on the transparency, I did not even consider experimenting with thickness as a variable. My case is 1mm thick, which is how thick the fresnel lens is too, but I’ll try printing something even thinner to see if it makes a difference.
Also, it looks like the Durable resin “simulates Polypropylene,” which is IR transparent, and as you suggested, I can likely go even thinner with that, so worth looking into. Thanks!
The “simulate PP” part is mostly for mechanical properties and general feeling. I wouldn’t bet on it mimicking optical properties, Durable is still a methacrylate.
the idea is that most IR lenses are designed to filter out MOST of the visible light spectrum.
either the sensors are bamboozled by too much wide spectrum light- or the lens itself is heated by the visible light and that heat radiates out as IR-
that is why outdoor motion sensors have a white lens- to reflect as much light as possible.
Durable is partially transparent- and acrylic, so it might not work- but you can make it more semi opaque by how you cure it. curing under water in sunlight results in a cloudy white plastic that reflects most incident light.
Also- the OP should try testing the materials in a Dark Room- if it works with the lights off, but not with the lights on, then its a problem with too much light swamping the sensor.
cheap alternate materials would be to Vacuum Form Polypropylene on a small vacuum former- which you can buy or even build pretty cost effectively for small parts.
use the Form 2 to print a solid vacuum forming buck that will draw a thin part the shape you need.
I experimented with a 0.5mm thin case and the sensor still could not pick up any activity. It’s not related to too much light either because the sensor works with absolutely no cover almost as well as when it has its original fresnel lens, but I confirmed by also testing in the dark and got the same results.
Therefore, i don’t think thickness or being too transparent is the issue. At this point, my guess is the resin formula includes something that blocks infrared light, which doesn’t give me much hope for the durable resin either
yeah- definitely rig up a simple vacuum former and pull the parts in sheet stock polyproplylene.
for small parts in thin stock they are relatively easy to set up.