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See through glass sensor ?

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truckdoctor

New Member
Hi eveyone , i have a question for all you experts i can't find an answer to.

What motion detector can i use as a switch to operate a device iv'e made in a shop window that detects passers by on the other side of the glass . Iv'e made it with a PIR and all was working well in the workshop and didn't realise that PIR's don't work through glass. Any idea what other sensors i could use?
Help please.
 

mneary

New Member
Is the glass coated with an IR barrier? I would normally expect a PIR to work, perhaps with reduced range. Maybe shield it from interior reflections.

You could mount it outside the shop window, maybe above in the eaves.
 

dknguyen

Well-Known Member
Most Helpful Member
Is there something like a PIR except with visible light? Even if there isn't, you could make a photodetector circuit that reacts to changes in the photo-detector's output.
 

truckdoctor

New Member
Help still required

No ;the glass is not coated ,we have PIR sensors in our house and have discovered that by placeing a sheet of glass over these they don't detect anything even at very cose range . I assume they detect heat and the glass acts as a barrier.
A light detection circuit sounds a good idea ,are there any circuit digrammes available on this site?
 

Sceadwian

Banned
It'd be a whole lot simpler to simply wire the sensor up outside. All it'd take is a single drill hole and re-wiring the sensor, but it near the top of the window and no one's even gonna notice it's there. Like mneary said if you have eaves it's even more perfect you can recess it up, completely out of site.

What about IR LED's as illumination? If they're bright enough it'll reflect off the people outside and set the PIR off? Worth testing at least.
 

truckdoctor

New Member
no hard fixing

Sorry i'm missleading you maybe , I cant hard fix anything to the shop ,this device will be inside the window as part of a display to sell items and may only be there for a few weeks until it's moved to another store so hard fixing anything is a bit too much . I thought about ultra sonics but think some form of light sensor is the only way forward , just don't no what to use .
 

Sceadwian

Banned
What about IR LED's? The increased IR illumination may make the PIR work through the glass, you'll just need to put the LED's right up next to the glass to avoid reflections.
 

Sceadwian

Banned
Ir = Infrared. It's a shot in the dark though not idea if it'd work or not but it would make sense to me. I'm just not sure what part of the IR spectrum PIR sensors are sensitive to. If it's far IR it's usless as IR leds are near IR.
 

ericgibbs

Well-Known Member
Most Helpful Member
Ir = Infrared. It's a shot in the dark though not idea if it'd work or not but it would make sense to me. I'm just not sure what part of the IR spectrum PIR sensors are sensitive to. If it's far IR it's usless as IR leds are near IR.
hi SC,
If the OP uses IR illumination a freq of 9.4micros is at a peak from the human body.

A problem could be caused by so much back reflection from the glass window that the shop inside could be swamped by IR.

I would suggest a simple web camera using some basic motion detection software in a PC.
 

Ross Craney

New Member
Hi eveyone , i have a question for all you experts i can't find an answer to.

What motion detector can i use as a switch to operate a device iv'e made in a shop window that detects passers by on the other side of the glass . Iv'e made it with a PIR and all was working well in the workshop and didn't realise that PIR's don't work through glass. Any idea what other sensors i could use?
Help please.
You are correct , PIRs won't work through glass. One of the older microwave only detectors would do the job.
 

gerty

Member

truckdoctor

New Member
micro wave

Thanks for the replies , microwave would seem a good bet and looking at whats available there is a vast choice .They emit radiation and are safe more that 50mm distance , doe's this mean they will do harm if closer?, i don't wan't to get cooked.
 

Sceadwian

Banned
Depends on the output power, I wouldn't put it close to living tissue though, even if you don't get 'cooked' the small localized heating is not good for the cells.
 

Mr RB

Well-Known Member
A little camera will do it. There's a small camera Kit sold for robotics that has a PIC or AVR included, and will provide output signal to track a red object, or tell if something has changed in the camera image. Like a "scene" sensor that tells you if there is movement in the scene.

I think I saw someone using the kit over at Seattle Robotics if you wanted to do a search.
 

Sceadwian

Banned

Ross Craney

New Member
Thanks for the replies , microwave would seem a good bet and looking at whats available there is a vast choice .They emit radiation and are safe more that 50mm distance , doe's this mean they will do harm if closer?, i don't wan't to get cooked.
Well I wouldn't strap it to my head but they are only a couple of mW. You run a higher risk with your cell phone.
 
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