PIR sensor behind glass?

Knox

@yo-less said in PIR sensor behind glass?:

Can a PIR sensor be covered by anything at all or does any kind of material automatically block motion detection?

Technically the sensor is covered by something, but that thing is the focusing Fresnel lens. Depending on the PIR you got, you’ll notice the plastic domed lens does come off rather easily.

“These curved segments are Fresnel lenses which constitute an array that increases the detection zone of the sensor. Fresnel lens array is known to capture more infrared radiation and focus it to a relatively smaller point. Detection is more stable and maximum distance for detection is also increased. Fresnel lens has been crafted to be translucent so that it can capture only infrared radiation without getting unwanted radiations from visible spectrum of light.”

Now the issue is that most glass and metals reflect IR wavelengths extremely well. So depending what the film/mirror backing is made out of may make your efforts mute. Aluminum which is used in most standard mirrors reflects all of the Infrared light in the spectrum.

So mounting it behind the mirror just doesn’t seem practical due to the way light works. So what I’m thinking of for me, is to mount it in a light fixture above the mirror. Not sure on the details yet but that’s where I am right now.
However the Camera trick does function very well and will give you that clean look.

yo-less

@Knox Yeah, thanks, my Fresnel lens isn’t even fixed to the PIR sensor and comes off right away if you don’t find some way of keeping it there ;-). But you’re right, didn’t think of that, it’s actually covered by this plastic dome. Maybe if I install the PIR sensor in the frame of the mirror and cover that section of the frame with acrylic glass, such as Plexiglas, it might work and look alright. Will try and test if my sensor detects IR behind a sheet of acrylic glass.

Knox

that would be a good test, but just note you’ll be lowering its effective area. Which for a mirror might be fine, as you normally stand directly infront of it.

yo-less

Sure, I guess I’d have to play around with its sensitivity, will keep you updated on the outcome of my tests

RedNax

Pir isn’t really an option behind glass. There’s a cam based solution which works through the mirror.

That said, my mirror is full sized and the pir peeks out the bottom… You’d never know it’s there unless you know where tot look…

Cato

@RedNax Can you share a picture? 😊

RedNax

@Cato No problem… anyone care to donate to the WWF Panda?
There’s a PIR sensor on the bottom of the mirror, out of eyesight. It detects … well… hot legs :D

yo-less

@RedNax Your mirror looks really cool.

Our mirror will be mounted pretty much at eye level so having the sensor at the bottom of the frame won’t be an option for me, but I’m already experimenting with covering the sensor with plastic stuff ^^.

Is there an xkcd module I’m not aware of?

And may I ask where you got your glass? Some of the pictures I’ve seen look like you can still see the monitor behind the glass but with your mirror that doesn’t seem to be the case.

RedNax

@yo-less Thanks!

The mirror is from a dutch webshop… At night, when there’s no other illumination you do see the backlight of the screen shining through… In the daytime it looks like the picture.
I’ve been pondering altering the backlight/brightness of the screen according to ambiant lightlevels… unfortunately this is only controllable by navigating the screens menu as opposed to discrete buttons…

Oh, and yes… there is: https://github.com/RedNax67/DailyXKCD

It’s forked from the original author… Ive added the random comic on non comic days…

yo-less

@RedNax Alright, is that the case with all types of glasses? I guess it would be?