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hello,
I'm trying to create a project with motion sensors that detects "hand swipes". I was thinking the easiest way was to have a beam brake using IR sensors and found the "sharp - Infrared Proximity Sensor" that works upto 80cm but I need 6 separate points of detection (or 6 switches) which gives a total cost of 6*10 = £60!!!!  smiley-eek ..bit too expensive!

I was wondering if there was a cheaper way to achieve motion detection. I notised while doing my research that the same thing could be done cheaper with some other IR detector and emitter pairs but I dont know enough to work out if the items i find will work with the distance I need.

So i guess I'm hoping someone can either guide me to a cheaper option or help me out with getting the right IR detector and emitter pair with a detection distance of around 1metre.

could really do with some help  smiley-red

Many thanks!
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hello,
I'm trying to create a project with motion sensors that detects "hand swipes". I was thinking the easiest way was to have a beam brake using IR sensors and found the "sharp - Infrared Proximity Sensor" that works upto 80cm but I need 6 separate points of detection (or 6 switches) which gives a total cost of 6*10 = £60!!!!  smiley-eek ..bit too expensive!

Using Sharp IR distance sensors to detect "swiping" of a hand (or other object) is severe overkill, unless you need the variable distance information that such sensors can give you.

I was wondering if there was a cheaper way to achieve motion detection. I notised while doing my research that the same thing could be done cheaper with some other IR detector and emitter pairs but I dont know enough to work out if the items i find will work with the distance I need.

So i guess I'm hoping someone can either guide me to a cheaper option or help me out with getting the right IR detector and emitter pair with a detection distance of around 1metre.

If all you need to do is detect a swipe, then what you would actually be doing is detecting the reflected infrared light from an IR LED bouncing back to a photo-transistor. Most photo-transistors are most sensitive in the IR region, but if you want to be absolutely certain, you'll need to purchase a "matched pair", or look at the datasheets for the LED and photo-transistor to come up with your own "matched pair".

You would then want to build something akin to a "beam break detector" - except in this case, the beam will -always- be broken, because you face both the emitter LED and detector photo-transistor in the same direction (when you hand gets in the way, the reflected IR light re-completes the "beam"); you might also want to put opaque tubes or something around each as "baffles" to prevent stray light from triggering the circuit, and possibly small lenses in front of one or the other (or both), to focus the light and allow for some measure of increasing the detection distance.

The beam-break detector can be dead simple (just hooking up the LED to an output, using a current limiting resistor, possible adding  a transistor to drive it with more current, depending on what the datasheet recommends; and hooking the IR transistor to an input), or it can be more complex, adding a small amplifier to the output of the photo-transistor, perhaps with some kind of comparator circuit.

So - do some googling on "beam break detectors" and "photo-transistors", "IR LEDs", etc - you'll eventually find something workable.
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Have you given any thought to using simple (cheap) photo resistors.  Set one up in a voltage divider and monitor the voltage.  As the light level on the resister goes up and down, so does the voltage.  So it will be able to tell if you cast a shadow over the sensor with your hand.  Of course that is also true of shadows for any other reason.

I saw one person using a laser pointer to signal a board.  In this case it was the opposite of a shadow.  There is nothing magical about IR other than you can't see it.

Just a thought.
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Hey thank you for your replies,

I agree, the sharp IR sensors are over kill which is why I wondered what else was out there.

I found this pair (i think they will work together) but like the other ones i found i have no idea what distances can be achieved:
Phototransistor: http://www.maplin.co.uk/infrared-phototransistor-2252
Emitter: http://www.maplin.co.uk/high-power-infrared-emitting-diode-2253
another Emitter: http://www.maplin.co.uk/3mm-infrared-emitting-diode-48038


I'm looking for something that can transmit over about 80cm. Could this pair really do that, or would i need to boost it's signal or oscillate something and if so how would i go about doing this?!

sorry for the simple questions, I'm a noob and I'm getting no luck on google
« Last Edit: June 16, 2012, 08:37:57 pm by 7immy » Logged

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Hey thank you for your replies,

I agree, the sharp IR sensors are over kill which is why I wondered what else was out there.

I found this pair (i think they will work together) but like the other ones i found i have no idea what distances can be achieved:
Phototransistor: http://www.maplin.co.uk/infrared-phototransistor-2252
Emitter: http://www.maplin.co.uk/high-power-infrared-emitting-diode-2253
another Emitter: http://www.maplin.co.uk/3mm-infrared-emitting-diode-48038


I'm looking for something that can transmit over about 80cm. Could this pair really do that, or would i need to boost it's signal or oscillate something and if so how would i go about doing this?!

sorry for the simple questions, I'm a noob and I'm getting no luck on google

Maybe you could better detail exactly what kind of hand swipe you're looking to detect.  Detecting a hand swipe 80cm away could be done with an IR emitter/receiver, but not maybe if your body was 100cm in front of the sensor as well.  Basically, knowing exactly what the situation is would allow others to better suggest what may work best.  For me, the problem with using IR to detect a hand swipe is that you may not be able to tell if it's a hand swipe 10cm away or someone walking by 100cm away.  If that doesn't matter for your situation, maybe IR will work.  I believe you would also need to know the distance to the object being swiped and not just that something is passing by at some unknown distance.  But, that's just a guess as we don't know exactly what you're trying to do in the exact environment.  You may want to consider a cheap ultrasonic sensor that can not only detect a swipe, but also the distance, which I believe would better work as a swipe detector.

Tim
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