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Laser pointers were on sale at Office Depot ($8.99 a pop, as I recall) so I thought I'd get a couple and make my RCX respond to them. Turns out it's really difficult -- your laser dot has to be absolutely spot on the photoreceptor of a Mindstorms light sensor to get a reaction and it's almost impossible to get the laser dot in the right place when you're, say, the other side of the room. This was driving me nuts, because I wanted to use the laser pointers for controlling the RCX, playing RCX laser tag, and so on. I was trying lenses, translucent Lego bricks, and everything I could think of to make the target larger.


...this little assembly allows the light sensor to respond to the laser pointer - I can hit it across the room every time, and the only part you'll need apart from the RIS is a piece of paper (I suppose you could always tear a piece out of the manual, if you want to be 100% Lego parts).

Just for the record, you need to take care with hand-held laser pointers - repeated exposure could damage your eyes so don't fool about with them: use them in a controlled way in environments where there's little chance of stray reflections (don't monkey with them near windows, for instance).

Also, although this works well indoors, it doesn't work well in outdoor sunlight (just so you don't waste time trying it).

LaserTarget, instruction sheet
ASSEMBLY (refer to picture above)

  1. Light sensor with 4x4 plate and a piece of white paper (ordinary paper from my laser printer tray - the paper weight is 20lb if you're American, 70 gsm if you're metric, but I doubt that the paper weight is critical). The piece of paper is cut to the same size as the 4x4 plate; the left and right sides of the paper are colored in red (or any color you like) so that the colored parts are the same thickness as a 1 x ? Lego brick. You push the paper down onto the studs of the 4x4 plate until the plates studs punch through.

  2. Two 1x4 plates are added to the sides of the 4x4 plate. One 1x2 Technic brick with a hole through it, with a 1x2 plate on top, is put in front of the light sensor. The 1x2 Technic brick eliminates most of the red light from the LED which is packaged with light sensor.

  3. Two 1x4 bricks are added to build up the walls on wither side of the light sensor. The paper is folded up and over, and punched down onto the studs of the 1x4 bricks.

  4. A 4x4 plate is added to the top and the assembly is finished. The target area for the laser pointer dot is the white part of the paper.

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