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Topic: How to detect people/motion through glas (Read 2046 times) previous topic - next topic


Hi *,

for a christmas project I need some advice. (OK - christmas 2013 - it's too late for this year  :smiley-roll:) Some background: in our office we have small windows next to the doors, as high as the door and 25 cm wide. I want to create some blinking stuff, which shall start, when someone passes. An ultrasonic sensor (srf04 or so) will not work, but what's about an IR sensor? Does it work through glass?

best regards

#define true '/'/'/'
#define false '-'-'-'


You can try setting up a beam, and a detector, IR might work too. If the beam is cut, it triggers your lights.
My GitHub:


which shall start, when someone passes.

Do you means passes through the door by the window?  Or passes by in some hallway?

How "tight" is the construction? Hung ceilings? Maybe get over the top of the window to the other side?

Or if there is any power on the opposite side, this MIGHT work through the glass, being higher power modulated IR:

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IR generally will not pass through glass but the near IR you use in remotes has some sort of penetration. You will need a reflector on the other side of the corridor to bounce the IR off.
It needs to be modulated but most of the IR receiver chips are meant for data not this sort of light barrier stuff.
However, the only one that I know of that is is the TSOP4038.


Since it's in the office and the ambient lighting will be fairly constant, I might try a simple CdS
cell [photoresistor] pickup on the Arduino ADC. The pickup will go dim, or at least probably change
quite a bit, when someone passes. You could test this in 10-minutes, have for Xmas-2012.

Something like this would probably work outside too if you rejected slow background lighting changes
and triggered only on quick changes. By gauging the rate-of-change, you could probably respond to
movements only in a certain range of velocities, ie normal walking speed.


start, when someone passes.

Could you explain what you mean by that? If you mean walks through the doorway, I guess you need some sort of beam-breaking system. But if you just mean walks past the window, a webcam with motion detection would achieve that using existing freely available software.
I only provide help via the forum - please do not contact me for private consultancy.


Dec 05, 2012, 09:13 pm Last Edit: Dec 05, 2012, 09:18 pm by danimath Reason: 1
Hi *,

OK - for clarification (sorry, it seems that my english got a little bit rusty :*)

I have attached an image of our typical office door (hope it works from my tablet  :)) You can see the hallway through the window. I will put the device (perhaps a sort of star or snowflake with 24 LEDs or so) onto the inside of the window. If a colleague walks down the hallway the LEDs shall start blinking (this is the easy part, I've prepared such a thing with shiftregisters). But alas I cannot install anything on the other side of the hallway (that would lead to trouble with the boss :-().

I've thought about a camera, but it seems a little overkill for this little project.

thanks to all and best regards

#define true '/'/'/'
#define false '-'-'-'


If all they are doing is walking past the door, then a beam cutting system will work or you can even put a IR/Ultrasonic distance sensor outside the door, and trigger the lights that way.

However if you want everything inside behind the glass then you may just want a Beam cutting system.
My GitHub:


Dec 05, 2012, 10:10 pm Last Edit: Dec 05, 2012, 10:54 pm by oric_dan(333) Reason: 1
Due to the illumination in that hallway, I'll bet every time someone walks down the
hall you perceive a definite dimming in your peripheral vision.

CdS cell inside side of glass [encased in a small shield to prevent pickup from inside
the office], 10-minutes work, Voila!


If the only time this display is on is when people can see it then why turn it off at all?
Just a philosophical point.


what if you use Passive Infra Red sensor and attach it to the ceiling? No.

I've had this issue before for a client work, I ended up using Kinect because it's IR is strong enough to see through a 2cm thick glass. You may wanna try it too :)


Many thanks for all your replies! I think I will try a PIR or a photoresistor. Because I have tons of other things to do before christmas I move this project to the next year. Perhaps a rabbit with red glowing eyes for easter (in Germany the "easter rabbit" hides chocolate for the children on easter morning  :)).

best regards and merry christmas

#define true '/'/'/'
#define false '-'-'-'

Runaway Pancake

I don't know how well it works through glass, but I can tell you that it works through walls and doors

"Who is like unto the beast? who is able to make war with him?"
When all else fails, check your wiring!


I would try parallax's PIR (passive infrared) sensor. It has a fairly large range so it may see a fair distance through the glass and it's cheap ($10).

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