I recently noticed Toot, which is a very neat project to make for kids.
I could not find any information on how these were made, so now I'm curious and started thinking how I could make something similar. For starters I'm looking for ideas on how to sense the proximity (and order) of the bricks. NFC sensors is obvious, but quite expensive if you need many. I also thought about placing magnet inside the bricks in a pattern and identify the adjacent brick by Hall effect sensors and the position of the magnets. But that would not allow for communication between the blocks.
If we have a hole on the side of each brick, IR would be easy and cheap.
You could put a coil (probably require quite a few turns - maybe 1000 or so) on the inside of each face of the box, and use that as an "air-gap" transformer to communicate...?
Cool! Have you seen the interview video here http://callmefe.de/toot? It looks like each box lights up a led for a brief time after it's done playing, so if another box is able to detect the light (ie it's aligned correctly) it will start playing too.
(Although, in the other video, the boxes don't appear to have any holes.)
That gives you a proximity/alignment sensor. Perhaps the rest of the communication happens through bluetooth. A smartphone is also part of the picture, and it appears it needs to be able to send data to each box individually, so it would make sense.
Maybe each box just sends a bluetooth message to the master when it's "chain playing" a sound: that way the master would be able to keep track of the order in which boxes are playing and take care of the more abstract stuff.
Forgetting about the more complex stuff related to box order and communication, I think it would be cool to have a modified setup with speaker on top and ir led based alignment/sync on the four sides. Then one could play with harmony, too.
Some boxes could even be triangular prisms, making it possible to form loops etc.
@cr0sh: That would have been really cool, but unless one can buy ready made coils it's not very practical to make oneself.
@barbaz:Yes, I saw the interview too, but did not notice the light and there actually is a hole in the side (at 00:09 it can be seen clearly). That explains a lot! I wonder if it is just a pulse, or if it can transfer data? Bluetooth could be used to transfer data, but is not really practical for synching the speakers as they can not all be connected at the same time.
I can think of several potential modes of operation:
Sample and play: As shown in first video, each block is a standalone sampler with speaker. The "head" initiates the sequence by blinking a light to the first box
Organize a pre-made tune: A phone could transfer premade sounds to the "head". Then the head could distribute these to the blocks, either by serial infrared (if it is fast enough). But that would require the child to join the head with the blocks one by one. Maybe too complicated. Alternatively you could have bluetooth in each block and let the head automatically connect to these one by one to transfer sound (That would drive up the price). Or they could use nrf24l01+, which is cheaper. I am currently using that in development of a sensor network.
Rythm boxIf one box can initiate the next box after a adjustable time interval (maybe before it's sound is finished playing), the boxes could be used as a simple rythm composer. Could be rather fun! Although radio would probably be the easiest (at least with my current experience), I'm feeling that there would be an extra sense of satisfaction doing this with infrared. Maybe half duplex serial communication...