The Sound Square

Posted on Feb 6, 2014

On the face of it the design of a Sound Square is simple, all you need are several Infra red beams across an opening and when ever you place your hand in it you break one of the beams. Simply detect which beam is broken and you know where about the square your hand is, then convert that position into a note. However, within that simple remit is alot of design and construction,

The Sound Square
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not only because of the number of components in the system but also trying to minimise the hardware required. I decided to mount my components on a frame made of angle aluminium, it was an asymmetrical piece with the two sides being 1" by 2. 5". I didn`t use anything more fancy than a saw and a drill. The whole thing is held together by 4BA nuts and bolts although you can use metric ones if you want. Having constructed a mount for the components now came time to design the electronics. The first problem was knowing how far apart I could put the beams. Too far and there would not be much resolution, too close together and the light from one beam would spread out and interfere with the next detector. I tackled this on three fronts, first of all I scoured the component catalogues for a narrow angled Infra red emitter. I found one in the OP298B, this has a half angle beam width of 25 degrees and a high light output, 4. 8mW at 100mA. A matching detector BPV11F was found with a half angle of 30 degrees. This is a photo transistor and has enough sensitivity to detect the beam without needing further amplification, further more it has a built in filter to minimise interference from visible light. In order to reduce the stray light further I then fitted 1" long tubes over the emitters and detectors. I made these from black art paper rolled twice round a pencil the same diameter as the sensor. The ends of the roll were fixed with a...

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