for a christmas project I need some advice. (OK - christmas 2013 - it's too late for this year ) 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?
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.
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.
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.
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.
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 :)).
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).