I'm working on a project and I need some ideas on how to sense the presence or absence of a large object through a piece of laminated glass. The sensing distance would need to be adjustable. I would like to be able to place the object a certain distance from the glass, and then adjust the sensor so that a relay opens when the object is present, but closes when the object moves out of range. I'm thinking of a range of about 10-12 feet. The range will vary between cycles, so that makes the adjustability necessary.
I found some microwave sensors that sound like they will work through glass. Is there something that would work better?
I'm really new to the arduino, so this should be a great learning experience for me.
The large object would be like a cargo shipping container. Steel, or maybe aluminum. Maybe 10' tall, 8 feet wide, color can vary. Could be smooth surface or have latches or other attachments. Could also be at some slight angle other than vertical. Not sure about reflectivity.
Laminated glass like windshields are made of. 2 layers of glass with a plastic sheet in between. Transparent.
A laser ranging system might work, if reflection from the glass is not a serious problem.
The LidarLite works very well and is supposed to be back in stock soon.
The LidarLite looks cool, but it's a little out of the price range of this project. I also don't really require the speed that it provides. Updating every few seconds would be plenty fast for what I'm doing.
I see laser emitters and receivers on ebay. Would it be possible to integrate these with an arduino?
Possibly. The cheap ones will not have a lot of power, so it will be difficult to differentiate between the signal and daylight.
I would drive it with the guts of a remote control. Those chips are readily available very cheaply. They get around the daylight problem by sending a modulated pulse and then the receiver picks out that pulse frequency from the large DC signal. Even the cheapest receivers can pick out a frequency signal that you can't see (even if it was a visible wavelength, like green.)
There may be commercial units available. If you're working with container-sized objects then the distances are much larger than normally used for optical sensors. Most things are built for assembly lines and bottling plants.
djreiswig:
The large object would be like a cargo shipping container. Steel, or maybe aluminum. Maybe 10' tall, 8 feet wide, color can vary. Could be smooth surface or have latches or other attachments. Could also be at some slight angle other than vertical. Not sure about reflectivity.
That big, eh?
"Metal detector" circuit - large induction loop mounted against glass. Measures effective inductance which increases when steel object is in field (or decreases with aluminium - so you can tell which!).
The "Ardutester" project uses the Arduino to measure inductance.
Any thoughts on this? http://blog.qartis.com/arduino-laser-distance-meter/
I'm not sure if it would read through glass or not, but I've read that the true laser range finders will.
I imagine saving the initial measurement, and then closing the relay if the measurement varies by a certain amount. Could have a button to re-measure/reset.
I appreciate your idea, but it doesn't seem like it would be very compact. That's also something I'm considering in this design. I failed to mention that initially. It looks like the laser idea could be put together in a small project box with the arduino.
I'm not ruling out any designs at this point.