# The chess challange.

1. May 23, 2013

### Tonino

I recently purchased a set of glass chess that are hollow and have sufficient space to fit a LED and some other components.

I woul like to power and lit The LEDs (up to 32) with induction current by installing a small coil an a capacitor connected in parallel inside each chess piece.
Another coil will be fit under the chess board, about 3-5 mm away from the surface of the board.
The cavity inside the chess pieces is about 15 mm wide.
Is it better to use thin wire or thicker wire?
I assume that the longer the wire (more loops) capture more power than fewer loops; am I right?
Can someone help to design a tuned pair of coils and related capacitors for this project?

thanks

Last edited: May 23, 2013
2. May 23, 2013

### Staff: Mentor

Welcome to the PF.

I'd suggest using a driven coil per chess square, instead of driving a big coil the size of the whole board. If you drive a big coil like that with enough power to light all the chess piece LEDs, you will probably demagnetize the credit cards in the pockets of the players... :tongue2:

3. May 23, 2013

### psparky

Either that or the scene from Spider Man 2 when Doc Oc gets the big fireball goin at the end and it pulls the entire building and everything into it.

I suppose it would make chess a lot more interesting:)

4. May 24, 2013

### Tonino

Definately has to be a coild for each board square (64 in all). The coils under the board can be big enough to cover most of the square (about 35mm) . Can someone help with the dimensioning of the coil, suggested wire gauge, N. of loops, frequency etc.?

5. May 24, 2013

### Staff: Mentor

To make construction easier, I would try 8 coils with 1x8 cells for each coil. You could even combine those coils to 2 coils with the same current pattern.

I think I would start with the LED part. How much power does it need? Which resonance frequency is achievable?

6. May 24, 2013

### Tonino

I don't really understand the '8 coils with 1X8 cells'. Does a cell correspond to a loop?
My ideas was to insert one small coil (about 15 mm wide) with a capacitor and a led all connected in parallel, into the chess cavity and attach a coil (can be up to 30mm wide) under each square in the chess board (for a total of 64 coils. I could have 8 rows of 8 coils under the board and power then in sequence. For the oscillator I could use a NE555 timer chip configuread as astable oscillator, for the sequencer I could use a CD4017 and the power unit could be made with ULN2003 (500ma X channel).
I believe I have no problem to design and build the driver part of the circuit. What I have problem with (because of my ignorance in the subject) is to dimension the coils and the resonant components.
I am not sure what is the best frequencies to use, here is where I need expert advice. I was thinking something in the range of 10Khz-100Khz. It all depends on component size (capacitor, and wire gauge) and best current transfer between the 2 coils. The current needed to lit a led is generally around 10-20ma. Considering that the led will be powered during half of the wave and only 1/8 of the time, current can be increased to obtain same brightness.

7. May 24, 2013

### Staff: Mentor

See the attachment, something like the left version instead of the right one.

I think the chess figures should get coil+capacitor+LED (all connected on both sides), where the driving coils use the resonance frequency of that system. The LED will get that part of the oscillation that goes beyond the LED threshold voltage.

Do you have some idea about the size of the coils that fit in the chess figures?

#### Attached Files:

• ###### chess.png
File size:
3 KB
Views:
55
8. May 24, 2013

### sophiecentaur

You could have a small magnet on the base of each chess piece which could be used to switch on only the coils under squares that are actually occupied. Only half the power needed when all the pieces are on the board.
Also, using 'horseshoe magnet' type cores would ensure good coupling.

9. May 24, 2013

### Tonino

Now I understand, and I think is a good idea to reduce number of drivers/coils.
As I mentioned before, the room available inside the chess pieces is equivalent to a cilinder 15mm wide and about 20mm high.
Sophiecetaur idea of attaching a small magnet at the bottom on the chess pieces and a reed switch under the board is good. If we want to take it to another level, then we could power the bottom coils constantly with a small current and detect when there is a perturbation the the current flowing through the (bottom) coils, condition that shoud happen when another closed coil is approaching.

Such a circuit is much more complicated and could be an extension of the project.
A similar project (using wires stretched on the board) that uses the same chess pieces, can be seen here:
http://www.instructables.com/id/LED-Chess-Set-Simple-Version/?ALLSTEPS