In fact I wrote some is not very good read, mainly because I'm lazy! Best to do so
Index = floater. Length;
Floater [index] = d.g etElementById (id);
Floater [index]. Style. Left = left + "px";
Wow, spammers are trying to blend in by posting code now... Impressive.
This could be done quite easily with RFID. You would need separate readers in every "slot" though.
I did something similar for a Capture the Flag prop, where the arduino needed to be able to tell what flag was in the flag holder. I put a set of pins on the bottom of the flag, and a socket in the flag holder. If the blocks dont have to be uniform, you could make some sort of 4 pin connector on the bottom, and give each block a unique pin configuration. For example, have 3 pins connect to input pins on the arduino, and the 4th pin connect to ground. Turn on the internal pull-ups on the 3 input pins. On block 1, leave all the pins unconnected, so when the block is "plugged in" the three input pins will read HIGH (because of the internal pull-up resistors). For block 2, connect the first pin to ground, and leave the others unconnected. Use a different configuration for the other 3 blocks.
If i'm just rambling, i'm sure someone else will come in here with a good idea.