        A simple rainbow maker from crap... you can find needed material lying useless at any home. if purchased, all these will not exceed few dollars.
       Can't be simpler... find a clock mechanism. you can use one that is faulty. if the seconds arm turns, its ok for us. find a crystal, you can use one from an old chandelier. find a solar cell. the one i used is from a garden lamp. other items needed:
        - some thin fishing rope or a paper clip.
        - window glass sucker-holder.
        - plastic wire wrap.

Step 1: Putting Things Together...

Attach the sucker-holder to the back of the clock mechanism. to do this i pinched 2 holes and used the cable wrap to tightly attach the sucker as shown in the image... note that we are attaching the sucker at the back, i.e. side of the battery compartment. this way, we can still place a battery and let the clockwork turn the seconds arm. at the other side of the mechanism (downside), clock arms are attached. we will only use the seconds arm. it will be placed tightly to the metal pin in the middle. just cut the long part of the seconds arm but leave few mm to tie the fishing rope.
Next hang the crystal to the center of the seconds arm with a thin fishing rope. you can use a modified paper clip for the purpose if you dont want the crystal swing to sides. plug the hung crystal to the center tightly, you can use some glue here but never let glue flow inside the mechanism. this may fix the gears inside. place a battery and attach the gadget to a sunny window with the sucker. at this point, the seconds arm must start turning and you must see dancing rainbows on the walls of the room, if the sun is shining on the crystal. if the mechanism doesn't start turning, that means your crystal is too heavy, find a lighter one...

Step 2: Adding Solar Power...

You don't need to use batteries for this rainbow maker because it will only work when the sun shines on it. no sun on the crystal, no rainbows around... :) so all we need to do is to power the gadget with solar power. you can use a 1,5 v solar panel for the purpose. you can find these on the solar garden lamps. i used one from an old garden lamp. just attach the red wire ( +) to the positive end of the battery compartment and the other color wire (-) to the negative end. you can just poke the wires to the back of the battery connection metals. or else, you can solder them and fix them. don't forget to turn the solar cells to the window... :)
You are done... place the gadget to a sunny window and watch many small rainbows dance on the walls and ceiling of the room...