How does the "Cool Circuits" game work? (sensing a closed circuit) I am playing a "Cool Circuits" game with my son and cannot figure out how it senses a circuit loop. The game is a clever invention by Penny Norman  (see video link here):
https://www.youtube.com/watch?v=rMFZ5Aezpsc
Here is a description the game:  There is a box powered by a battery.  The box has some unknown electrical stuff going on inside. You place eight passive components (each containing a piece of wire) on top of the box. When the eight components are connected to form a continuous loop, a “success” is triggered (the box plays music).  How does the box detect a success? 
I am guessing the box emits a magnetic field. The creation of a loop creates a change in inductance, and this change is sensed. The baffling things are: 
1) It detects a loop, regardless of the area of the loop.
2) It can tell the difference between using the eight pieces to make 1 continuous loop versus 2 separate loops (the latter case does not trigger a success). 
One possibility is that the device is sensitively tuned to the 40 different inductances formed by each of the 40 solutions in the game, and is so sensitive that it detects these and only these inductances.  But this seems overly-complicated. I do not know how to contact the inventor, so I thought someone on this community might be able to figure it out. Perhaps there is a simple E-M principle that I am forgetting...?  
 A: I'm going to agree with you and guess that it involves magnetic induction, too. As for ensuring some selectivity and not lighting up whenever someone puts just any closed loop down, or puts down two closed loops, I think that there are ways of conveniently doing that. For example, there could be simple wire coil loops around each of the 25 individual dot location of the puzzle. These 25 individual wire coils could be used for either generating an AC magnetic field at their particular location OR as a sensing coil to see if there is an AC magnetic field at their particular location.
If the electronics wants to check if a single loop of the correct size and shape was placed on the board, then it would send an AC current through one of the individual wire coils located inside the shape of the correct solution closed loop. That will cause an induced AC electrical current in the closed loop which was constructed by the player which, in turn, will generate a magnetic field at all of the dot locations within this closed loop. It's then a simple matter for the game's electronics to check to see if a significant induced AC voltage is detected at all of the other sensing wire coil dot locations within what is the proper solution closed loop region. If the game's electronics detects induced AC voltages from all of the proper positions on the game board, then it announces "Success" with its flashing light pattern.
A: I took it apart and saw there is very thin copper wire wrapped around the outside of the playing board. That tells me that the individual dots hypothesis doesn't work. There was no visible magnets inside it, the only magnet that I am aware of in the device is the magnet in the speaker.  Like you,I suspect it is using inductance in order for it to work. It must be a very small amount for it to trigger the light and music circuit, for there is no noticeable magnectic field around it. I put some very small metallic materials around the area of it to see if they would be attracted to anything and they were not. I am still learning about electronics so not a pro at this by any means. Is there an instrument one can use to search for a magnetic fields, similar to a voltmeter? Maybe I could try to take it apart and sprinkle very thin metal shavings around it to see if field lines is formed. 
A: After some more thoughts, I will attempt to "answer my own question." 
Here is what I think is going on: Since the 40 game solutions all have the same length, I am guessing their total areas are close enough so they all form inductances within some specified range.   For the two-loop example (which is not one of the intended game solutions):  I suspect there may be some coupling between the loops, so the overall inductance falls out of sensing range.  My son’s two-loop solution has the two loops completely separated (one is not inside the other), and so I think there is a partial inductance cancellation. This could explain why the device cannot detect this particular 2-loop solution. 
As an aside: It is interesting that my son found a two-loop solution that is consistent with the card hints and uses all 8 pieces, I think it was card number 16.  So the claim that "there is only one solution to each puzzle" is not true if one allows for two-loop solutions! 
A: Ok here is my hypothesis. When the switch is turned in the on position (either to flash the lights or to flash and include the music) it runs a current through the wire, creating a magnetic field. When the circuit is complete it is able to measure the change in induction. How I don't know. It going to take it apart again and look at the board.  Perhaps there is a Ensor of some sort on there. Fun stuff. 
I took it apart and attached some pictures. I got one of the board. I don't see any sensors on it, but again I am pretty inexperienced. Anyone see anything on there?
