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61  Using Arduino / Project Guidance / Re: Identifying Chess pieces in a Chess board on: September 30, 2013, 04:27:31 pm

The problem is that there will be inductive coupling between the antenna so no amount of switching is going to isolate one token.

So if the muxes are used to select the transmitter in column 'B' and the receiver in row 'B' what you are saying is that the transmitters in columns 'A' and 'C' will also fire and the receiver will see multiple tags is that correct?

Is there no way round this by say reducing the transmitter power (the rfid tags will be right on top of the transmitters) and by grounding the transmitters that are not supposed to fire?

62  Using Arduino / Project Guidance / Re: Simplest physical setup for Arduino to switch between two modes? on: September 30, 2013, 07:02:34 am
Info on inputs and internal resistors here;
63  Using Arduino / Project Guidance / Re: Human Motion Sensing Applications on: September 30, 2013, 05:02:56 am
Phew, I thought this was going to be an electronic nose project.

You are not planning on strapping the Arduino to an ankle are you?
There may be algorithms published already for this, you should search for them. Otherwise do it empirically, gather data when walking, jogging, sprinting, climbing stairs etc. look for a pattern in the data that characterises each motion then write software that looks for the pattern.
You are going to get differences in acceleration and frequency of motion for one thing.
64  Using Arduino / Project Guidance / Re: Identifying Chess pieces in a Chess board on: September 30, 2013, 03:46:19 am
Have to start working on this.. It will be a challenging task for me specially when come to the design of antennas by moderating sensitivity and signal strength(at most 1cm) by considering the dimension of standard Chess Board.
I would test the theory by using one transmitter and one receiver at right angles with firstly a single rfid above the intersection , then with rfids also on adjacent squares.

One problem might be the transmitter firing rfids other than the one at the intersection. You might be able to make the rfids more directional by placing tin-foil caps over them so that they only "see" downwards.
65  Community / Bar Sport / Re: Surrealistic Rubik's Cube robot [Auto-solver] on: September 30, 2013, 03:37:40 am
Hi Palliser,
Your mathworld link seems clearer. It gives the possible states as;
(8! 38 12! 212)/( 2.3.2)=43,252,003,274,489,856,000

I can sort of see where the equation comes from.
There are 8 corner mini-cubes each of which have 3 colors, and there are 12 edge mini-cubes each of which have 2 colors - so that is where the numerator comes from. I am not sure about the denominator.

Anyway its clear this is a very big number so brute force to precalculate solving the cube is not on. And yet any cube can be solved in at most 20 moves!

There are algorithms for solving the cube so that bit of the project can be done, though I expect most use far more than 20 moves.

The LED solution would be a lot more achievable but not nearly as exciting as seening a cube move, particularly if external wires could be avoided.

66  Community / Bar Sport / Re: Surrealistic Rubik's Cube robot [Auto-solver] on: September 29, 2013, 02:43:35 pm
The math is discussed briefly on wiki
Well that pins it down to all cubes being solved in at most 20 moves.

I don't understand how they are calculating the number of states though;
The original (3×3×3) Rubik's Cube has eight corners and twelve edges. There are 8! (40,320) ways to arrange the corner cubes. Seven can be oriented independently, and the orientation of the eighth depends on the preceding seven, giving 37 (2,187) possibilities.

How can there be 40,320 ways to arrange the corers but only 2,187 possibilities?
67  Using Arduino / Project Guidance / Re: Identifying Chess pieces in a Chess board on: September 29, 2013, 02:25:35 pm
This RFID project of mine uses exactly half the number of readers you would need.
That is a great piece of work.

Are you saying though that polymorphs idea of having eight transmitters for each row and eight receivers for each column would not work?
68  Using Arduino / Project Guidance / Re: Identifying Chess pieces in a Chess board on: September 29, 2013, 09:02:12 am
kasun could you not have made a neater drawing  smiley-grin

That is exactly how I saw polymorphs idea.
I am not sure why you have a clock though, I expected the Arduino to select the transmitter and receiver.

69  Community / Bar Sport / Re: Surrealistic Rubik's Cube robot [Auto-solver] on: September 29, 2013, 08:55:31 am
This seems like a very tough nut to crack but you could do it - good luck and be sure to post the outcome.

I am still interested to know how many states a Rubik's cube has can anybody do the maths?

Boffin1 I had not though of the playing videos backwards - very devious.
With the cube I resort to peeling of the colors and sticking them back on.

70  Community / Bar Sport / Re: Surrealistic Rubik's Cube robot [Auto-solver] on: September 28, 2013, 01:10:17 pm
Like I said I think this is an excellent idea, but there are enormous practical problems.
Boffin1 is right bout the servos, a fair bit of force is required to move the faces.

Can anybody say how many states a rubik's cube actually has?
In other words how many unique combinations can one be scrambled into.

Also don't you wish you had a real talent and skill like this;

71  Using Arduino / Project Guidance / Re: Identifying Chess pieces in a Chess board on: September 28, 2013, 01:02:21 pm
Polymorph's idea sounds plausible and, assuming it works, you get unique identification of each piece.

Another way with the reed switches is to have an extra 7 squares off to the side of each player (14 in total) on which players are obliged to place any major pieces they capture. That way it becomes possible to determine if a player has decided to promote a pawn to a queen, rook, bishop or knight. This means though that you need magnets in all the pieces plus 78 squares fitted with reed switches.

However if polymorph's idea is correct you could uniquely identify each piece and have much simpler code. You would need RFIDs in each piece (and cheap passive ones would probably be best), plus 8 transmitter coils and 8 receiver coils. This seems like the prime candidate to me.

72  Community / Bar Sport / Re: Surrealistic Rubik's Cube robot [Auto-solver] on: September 27, 2013, 10:28:59 am
A Rubik's cube 'appears' to be made of 3x3x3 smaller cubes.
However there is no central cube so that reduces to 26.

Of these cubes there are;
8 corner cubes3 faces visible each24 faces total
12 centre of edge cubes2 faces visible each24 faces total
6 central cubes1 face visible each6 faces total
26 cubes total 54 faces total

That sounds a lot but of course the cubes are not really free to move at random.
Maybe it would be possible to brute force the cube and calculate in advance the shortest path from any starting point?

73  Using Arduino / Project Guidance / Re: Identifying Chess pieces in a Chess board on: September 27, 2013, 07:29:11 am
Here is a chess set that says it is magnetic. Still not sure how it works though. What is the pillar at the back left of the board? How does the computer figure out what piece is on what square?

I presume the chess men are all passive?
Is there some kind of reader under each square and how can it tell one piece from another?

Maybe I am making too much of this, perhaps you don;t need to "read" the identity of each piece, how about this;

If you have a fairly strong magnet in each piece and a magnetic reed switch under each square you probably don't need to know by reading which piece is which. Instead you just make the assumption that the players set up the board correctly, that white makes the first move and that all the moves are legal. Then, with a knowledge of the rules, the computer can calculate what is on each square.

Pawn promotion is a snag though because you cannot assume it will be a Queen and, even after it moves, you still might not know what it is. i think manual input for promotion might be required.
74  Using Arduino / Project Guidance / Re: Identifying Chess pieces in a Chess board on: September 27, 2013, 07:10:23 am
Passive RFID tags would let you tag each piece cheaply.
The problem is reading the tags and knowing which of the 64 squares each piece is on.

There are existing computer chess boards how do they work?
75  Community / Gigs and Collaborations / Re: WIRE LENGTH MEASURE AND CUTTER on: September 27, 2013, 07:01:04 am
You need to expain your design, how;
  • does the wire come is it on drums
  • were you thinking of measuring the lengths
  • will the wire be fed into the cutter
  • fast does the system have to operate
  • will the wire be clamped in position during cutting
  • will you know the wire has been cut
  • is the cut wire removed

Will you use a PC to provide the interface to the Arduio e.g. to tell it what length you want cut, how many pieces and the wire dia?

The mechanical aspects of this project are probably the difficult bit.
You probably will not need much IO and the control logic should be relatively simple, but you should firm up the physical design first.

Also you should say what skills you and your son have. Have you done anything like this before are you good at building machines and working with electricity, do you have programming and electronics experience.

There are sites on the internet that let you load pictures then you can post a link to them. The other thread posted a picture and it makes it a lot clearer to people what you are trying to do.

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