7immy:
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!!!! 
..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.
7immy:
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.
