I need a sensor to detect the presence of an object on the other side of a plastic wall.

Originally I thought of using an ultrasonic sensor but the range I am working with is about 10mm. Most ultrasonic devices I have seen have a minimum range of 200mm, far too big.

Can anyone suggest another sensor? Or somewhere where I can get short range ultrasonic sensors.

Thanks
John

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Ultrasonics isn't likely to work through the 'wall' anyway, the plastic wall will reflect the ultrasonic back all the time.

You don't really give enough details to suggest other sensors?, it depends a great deal what it is you're trying to sense, and how big it is. A possibility is IR, but again the wall will stop it - but a transparent window (or the LED and sensor poking through) would work. Sharp actually make rather nice little IR sensors, which measure short distances (they work by measuring the angle of the reflected IR).

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I was thinking that I could ignore the reflection from the wall because it would always come at a specific time after the ultrasonic pulse is sent out.

For a given distance from the sensor, the reflected pulse would always come at a certain time. If I only look for the reflection at this time I can be sure it is the object I am detecting.

Is this thinking correct??




I am trying to sense the presence of an object, or multiple objects on the other side of the wall, up to 1cm past it.

The object can be any colour (including black or white) and is not flat.


I suppose I could cut a small window, although it is not ideal. Would the IR sensor you mention detect an object that isnt flat? Would it have trouble with the colour of the object?




Thanks for your help, as always :P

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Any possible reflection from the other side of the 'wall' is likely to be very much attenuated, and lost in the massive reflection off the original surface.

They are obviously affected by the colour to some extent, you would need to test them.

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How about a capacitive type proximity sensor? You could even dismantle a 20 dollar stud ( used by builders to locate wall framing ) finder for a working arrangement.

 

ir led is the best bet for small to medium range proximity sensing. ir leds can be programmed work at any frequency using timing circuits.

a dual reflective sensor, which encases an ir led and a phototransistor can be used. the phototransistor detects the reflected ir rays. the current at the collector of phototransistor depends on the intensity of incident ir rays which again depends on the distance of the reflecting object. the frequency of current would be the same as the operating frequency provided doppler effect is neglected owing to small distances

 

What is the "object" made of?

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